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Elekta Neuromag® System Hardware

1. 66 6 3 2 Normal powerup e ssessssersssssssssesssuurennrrrrrorrrrnessnesernrneserrenree 67 6 3 3 Power shutdown eeeeessseeseesessersssesssrssrrrseersrennsrunerensreesrrenne 68 NM20215A G 6 4 Protection e RM nest lient BA FUSOS nn ane Re te eds GA 2 LIMItnNg CICUS rs san Rens nb st ie 6 4 3 Undervoltage detection cccccccccceesscsessesceenseeeeeteeeetereeeeeees 6 4 4 Overtemperature protection VV 6 5 Cooling ANSE eee ones mani 6 6 Resetting Ine GIeCtrOniCS Tes ie iinta aatar a eaea 7 Auxiliary electronics 7 1 Interface to stimulus electronics ss LAS ANOUN Le RS nd ns se 7 4 2 Instructions TOF SO isirmnnsmdtihesntinntenes 7 2 Ed 5 ALES LL AEE A T E N 7 3 Voice intercom system option ss TB General sans nn en Ni a ia 7 90 USA o AEAT E 7 4 Video monitoring system option TAN 3 GBneral sn cede aus ne AR NN AA A Eiai HAT ISAS ihc nds SO en E 75 Audio electrons vices nn dan ee nn anni en cesse n ne de 7 6 Analog INPUT Sn a en Ren e ani 8 Maintenance 8 1 Maintenance program sessions 8 2 Checkup before every measurement 8 3 Noise level follow up and MEG channel tuning 0 c ceeceeeeseeeseeeeeeeeeeees 8 4 EEG Channel CHECKING soma bab aatva eosne rd amie a Na 8 5 VIMOUDIGSIOOUING cx cecil sans ci a an ei fu nn 8 6 Monitoring the liquid Helium level 872 Cleaning se none nds RE de 8 8 Coating of Ag A
2. 40 Safety instructions and precautions explained to all staff involved in the use of the system They should also BE NOTE It is recommended that the meaning of the ESD symbol should be receive training covering the precautionary procedures described below The properly grounded and shielded cabinets and racks are the most effective shield against damage In normal operation there are no parts inside the MEG electronics cabinet or the gantry top part the user needs to access Do not remove covers and do keep the cabinet doors closed Do not touch the pins of connectors or cables the electronics back plane or the electronics boards before grounding yourself properly Ground yourself with a grounding wrist strap or by touching any metallic parts of the magnetically shielded room or inside the electron ics cabinets To minimize the danger of electric shock it is recom mended to use a grounding strap specially made for this purpose that contains a built in series resistance Connect it to the cabinet frame or magnetically shielded room wall To prevent static electricity discharge to preamplifiers while connect ing or disconnecting head position indicator coils EEG electrodes or electrode caps the relative humidity of the air inside the magnetically shielded room should be over 30 preferably between 40 and 70 see Site Planning Guide Leave electronics service to trained service personnel Do not disconnect the electr
3. Fig 1 22 Liquid Helium level meter nes ee building Safety relief system Dewar Outside Transfer siphon Evaporated gas Exhaust line of the pAr Arar ere te not pressurized building i or nu gas Liquid Helium recovery system Storage Helium Level SQUID Container probe Sensors a Fig 1 22 Block diagram of the liquid and gaseous helium systems NM20215A G 27 Safety instructions and pre cautions CAUTION This section contains important information concerning the safe use of the system and maintaining reliable operation Read the instructions entirely before using the system 2 1 Use of liquid Helium 2 1 1 The Dewar is a vacuum insulated vessel containing liquid Helium at a cryogenic temperature Since the cold liquid is potentially dangerous certain precautions must be made in order to assure completely safe operation of the device Properties of Helium Helium liquid or gas is nonflammable and nontoxic Helium is one of the noble gases He Ne Ar Kr Ra Helium gas is odorless and colorless Helium gas is seven times lighter than air Helium gas is not life supporting it may replace air thus reducing the relative oxygen content in closed rooms if evaporated rapidly in large quantities resulting in a risk of suffocation Boiling point 4 2 K 269 C or 452 F Density of liquid 0 125 kg liter The liquid evaporates very easily latent heat of ev
4. For safety reasons it is however highly recommended that another person is present to assist or call for help in possible abnormal conditions This is especially important if the transfer is carried out off hours CAUTION Do not leave anybody alone inside a closed magnetically shielded room without the presence of another person outside the room e The liquid Helium level and boil off rate should be monitored regular ly Substantial increase of boiloff rate may indicate the need to re evacuate the vacuum The vacuum pump out must be left to trained service personnel e See also Section 2 1 3 concerning cryopumping Cryopumping At liquid Helium temperature all common materials are solid This means that the vapor pressure of for example the atmospheric gases nitrogen oxygen water is practically zero in any volume containing liquid NM20215A G Safety instructions and precautions 2 Ci Helium which leads to cryopumping of these gases any Helium vessel left open to atmosphere will very effectively suck in large amounts of these gases Water freezes and may block the Helium vessel or a transfer siphon Oxygen in the probe unit Dewar causes large irregular low frequency drifts of MEG signals because the magnetic susceptibility of the paramagnetic oxygen in its solid form is very high NOTE To prevent cryopumping observe the following precautions e All Helium vessels must be sealed from the atmosphere and properly vented vi
5. The Helium level probe is switched on and off by pressing the toggle button on the local display The reading stabilizes in about 20 30 s Each LED in the display corresponds to 1 6 percent NOTE Remember to switch off the probe after taking a reading by pressing the toggle button again If the probe is on extra noise will appear and the boiloff will increase NM20215A G NM20215A G Cryogenics Neck plug Helium level gauge Figure 4 1 Location of the Helium level gauge The Helium level probe does not cover the whole Helium space A zero reading in seated position corresponds to a level where all the sensors are barely immersed in liquid Helium while the 100 percent reading level in seated position the He level is close to the lower edge of the neck plug Refer to Table 1 for actual values in both seated and supine positions The normal boil off rate is about 8 liters day corresponding to a transfer interval of one week When the Helium probe reading is Zero there is still about 13 liters of liquid in the helmet shaped part of the Dewar A refill should however soon follow When you have checked the Helium level estimate whether zero level is reached before the next scheduled refill If this is the case schedule an extra refill The liquid Helium level and boiloff rate should be monitored regularly Substantial increase of boiloff rate may indicate the need to re evacuate the vacuum The vacuum pump out
6. The head position indicator system is based on coils see Fig 1 16 placed on known locations on the head A single coil can be energized by a coil driver card with currents of different frequencies The excitation signal is provided by the data acquisition system A 3 dimensional Fastrak digitizer manufacturer Polhemus Inc USA see Fig 1 17 is connected to the computer system It is used in the preparation phase before MEG measurement to digitize the positions of the head position indicator coils as well as the landmarks on the head which are visible in the MRI scan The locations of the landmarks are used Fig 1 16 Head position indicator coils 23 Overview of the systen Fig 1 17 3 D digitizer unit The transmitter coil closest to the unit digitizing pen and goggles with separate reference receiver leftmost are also shown Fig 1 18 Wooden chair for digitization to establishing a coordinate transformation between MEG and MRI magnetic resonance imaging data To allow slight movements of the patient during the digitization non magnetic goggles with a separate reference receiver are provided The transmitter of the 3 D digitizing system is attached to the back of the digitization chair see Fig 1 18 The liquid Helium level inside the Dewar is measured with a supercon ductive probe whose resistance is dependent on the length of the part immersed in liquid The meter board reads the resistance and conv
7. The vacuum lock is operated with a separate vacuum valve adapter CAUTION The exhaust line must be open at all times e The exhaust line should be reasonably leaktight and lead out of the magnetically shielded room to open air or to the recovery system The magnetically shielded room must be properly ventilated For details see Elekta Neuromag Site Planning Guide The overpressure inside the Dewar with respect to atmospheric pressure should be kept below 10 kPa 0 1 bar even during refill Should the pressure rise a safety relief valve will open at 10 kPa 0 1 bar If for some reason the pressure rises even further a rupturing membrane will break approximately at 60 kPa 0 6 bar letting gaseous Helium to escape via the safety exhaust duct to the outside of the building The fixed L siphon used in the Helium refills and located on top of the Dewar is normally sealed with a plug that has an additional relief valve which effectively vents the cold Helium space directly into the atmosphere through the siphon in the unlikely case all other exhaust routes get blocked When transferring liquid Helium transfer instructions should be obeyed see chapter 4 4 CAUTION To prevent frostbite avoid contact with liquid Helium or exhaust gas or any objects that have recently been in direct contact with liquid or evaporated gas Wear protective gloves and safety goggles Transfer of liquid Helium can be carried out by a single person
8. i ee 15V Ste pe Power input fi z Elekta Neuromag Oy k O OU Helsinki Finland amp Figure 6 3 Back panel of a main electronic power supply unit 68 NM20215A G Electronics g 6 4 2 6 4 3 Lij NM20215A G Power supply MEG Front End EEG front end isolated 24V AC power av i aw indicator __ se LEDs 4 nca ev Primary fuses Power switch 7a E Power input E Y a CJ Figure 6 4 Back panel of the preamplifier power supply unit All mains primary circuits of the power supply units are fused All fuses are accessible at the back planes of the power supply units with the correct values of the fuses marked in the immediate vicinity for details see Figs 6 3 and 6 4 A T before the rated current in amperes indicates slow time lag type and an F fast type If no type has been indicated use fast type fuses Main electronic power supply units have a spare fuse in the fuse holder Limiting circuits The main elecronics power supply units and the preamplifier power supply unit have fuses and or current limiting circuits on the low voltage side NOTE If any output current of a main electronics power supply unit exceeds its limit the unit will turn off all its output voltages and the indicator LED for that voltage will turn red If a current limit shutdown occurs try restarting the unit by detaching its power cord wait unit the red ind
9. B component which is perpendicular to the surface of the detector of the field 102 planar gradiometers measuring the gradient 0B ox and 102 planar gradiometers measuring 0B dy component of the gradient The sensors are arranged in triple sensor elements each comprising two orthogonal planar gradiometers and one magnetomer in the same plane as the planar gradiometers For geometrical details see Fig 1 6 NM20215A G Overview of the system 1 The helmet shaped cryogenic Dewar is a vacuum insulated vessel to keep the liquid Helium necessary for cooling the SQUID sensors to 4 2 K It is a double wall structure with vacuum gap and additional thermal radiation shielding in between The neck plug of the probe unit also provides thermal insulation The main dimensions of the helmet are shown in Fig 1 7 1 5 Channel layout Ci Layout of MEG channels is shown in Fig 1 8 a The naming of individual channels is based on a hierarchical system see Fig 1 8 b Each channel is identified with a 4 digit number xxyz The two most significant digits in a channel number e g Olyz define a group of neighboring sensor elements The first group Olyz is on the frontal left edge of the array the last group 26yz is on the right edge of the array The third digit specifies an individual sensor in a group Typically four sensors belong into a group E g xx2z is the second sensor in a group The least significant
10. a hand held shower A soft small brush can also be used Use ordinary soap or mild dish care detergent such as Fairy if necessary to clean the residue Be careful not to let water into the D37 connectors Allow to dry Pure alcohol can be used for disinfection Do not leave old paste to harden in the electrode cavity as it may be difficult to remove later The white cover of the phantom can be cleaned with with soap water or ordinary mild dish care detergent NM20215A G Maintenance E Ci The computers and their displays included in the system must be cleaned with agents and wipes specifically designed for this purpose Do not spill liquids inside the keyboards or other devices where they can cause short circuits and damage to the devices Note When cleaning the gantry especially the interior of the helmet outer surface of the helmet observe that risk of flux trapping to sensors exists resulting in artefacts Therefore magnetic objects like wristwatch es belt buckles magnetic buttons on sleeves etc must not be brought in the vicinity of the Dewar Refer to chapter 2 4 8 8 Coating of Ag AgCl electrodes The sintered Ag AgCl electrodes such as used in the Elekta Neuromag EEG cap do not need chloriding To coat solid metal Ag AgCl electrodes immerse the single electrodes and the electrode cap with electrodes in place into a saline NaCl solution Use about one tablespoon of NaCl per one liter of water Draw a
11. cabinet keep the doors closed This also helps to reduce the acoustic noise from the fans The roof fans operate always when the cabinet main switch is on Their speed is temperature controlled to reduce acoustic noise Do not alter the temperature setting NM20215A G Electronics g 6 6 Resetting the electronics Each main electronics board MEG and EEG has a recessed reset switch on its front panel If the board becomes locked up e g showing red fail light or it stops responding to commands press reset switch Boot up of the boards starts automatically Wait until the board shows steady green run lights and the fail lights are off Boot up takes about 30 60 seconds If the bootup fails open the back door of the main electronics cabinet and check the indicator LEDs of individual power supplies see Fig 6 3 If several boards fail simultaneously all boards can be reset simulta neously by pressing the reset switch of the System Controller Board SCC which is located on the rightmost slot of the second MEG rack After resetting the boards run Restart acquisition programs by double clicking its icon in the Maintenance toolbox on the acquisition worksta tion NM20215A G 71 7 Auxiliary electronics 7 1 Interface to stimulus electronics 7 1 1 72 Introduction The stimulus I O system is used to synchronize external stimulators and MEG signal averaging Two modes of synchroniza
12. constantly monitored watching for any artefacts Magnetic impurities left on the subject may cause severe artefacts they should be removed When enough data has been collected stop acquisition and stimulation Determine if additional recordings using e g a different experimental condition are necessary Keep experimental log of recordings stimulation conditions and trigger line assignments etc For details of the data acquisition software and on running the experi ment see Data Acquisition Reference Manual When the measurements have been finished open the door of the magnetically shielded room Disconnect the HPI coil set and electrodes or electrode caps from the corresponding connectors Remove stimulator leads and actuators as needed If seated measurement position was used release the elevation mecha nism of the chair and pull the chair from underneath the Dewar In supine measurement position release the lock of the upper bed and pull the upper bed away from the gantry Support the subjects head if appropriate Lock the upper bed again Help the patient to come out of the magnetically shielded room Remove the head position indicator coils and electrodes and clean them see Chapter 8 7 The cap can normally be removed easily from subject s head If it does not get loose easily wet the cap and hair with a hand shower Be careful not to get water into the 37 pin connectors The paste and gel can be removed from the hair by
13. digit is used to distinguish between three orthogonal channels of a single sensor element Value 1 is always used for magnetometer channels Values 2 and 3 are used for the planar gradiometers E g xxy3 is a planar gradiometer channel of a sensor element NOTE The value 2 may refer to the derivative along either latitude or longitude depending on the location of the sensor Same applies to value 3 For details of the naming convention see Fig 1 8 b Locations of the various sensor groups are illustrated in Fig 1 9 a 1 9 b and 1 9 c 1 6 Gantry bed and chair NM20215A G Gantry bed and chair comprise a system to position the head of the subject patient in the sensor array inside the Dewar The gantry is used either with the bed or with the chair depending whether measurements are made in supine or seated position The gantry allows positioning of the Dewar in either supine or upright position see Fig 1 10 a and 1 10 b The movement between the two measurement positions is motor driven The patient bed provides a comfortable supine measurement position The chair provides seated measurement position which is the de facto standard in cognitive studies For details of the construction and usage see Chapter 5 1 Overview of the systen Top view Front The helmet shaped For naming convention and Layout of the sensor elements 8 a 1 sensor array i
14. e magnetic field lines cannot penetrate the superconductor Trapped flux NM20215A G A phenomenom where magnetic flux is trapped in supreconducting structures e g thin films A superconductor normally repels magnetic flux However if regions of the superconcutor become non supercon ducting as a result of being exposed to strong magnetic fields magnetic field lines can enter the superconductor and become trapped inside superconducting areas May lead to deteriorated operation and increased noise of the SQUID sensor Movements of the trapped flux are seen as magnetic signal jumps Trapped flux can be released by heating the superconductor above its superconducting transition temperature typi cally over 10 K 93 ELEKTA Elekta Neuromag Oy P O Box 68 FIN 00511 Helsinki Finland Tel 358 9 756 2400 Fax 358 9 756 24011 E mail neuromag neuromag fi Web www neuromag com
15. in Table 2 The radius of the hemispherical plastic cover is 87 5 mm The fixed head position coils can also be used in checking the operation of the 3D digitizing unit NM20215A G Auxiliary electronics HPI coil left Connector panel under the gantry cover Phantom HPI cable Pin arrangement Phantom cable a ai dipole 1 a aj dipole2 a dipole 31 a a dipole 32 Dipole multiplexer Figure 7 2 The phantom A phantom measurement is basically similar to an ordinary evoked response measurement with HPI coil digitization etc This is to check the accuracy of the whole measurement chain comprising HPI coil digitiza tion data acquisition and dipole source analysis For details of the measurement procedure refer to Data Acquisition User s Manual Connect the phantom excitation multiplexer into the cable with a 25 pin connector which is under the side cover of the gantry Start the acquisition program Select or create a project suitable for phantom measurement Load the required measurement settings from a template file Pick Load measurement settings from the File menu and select the file neuro dacq setup phantom fif Digitize the HPI coil locations on the phantom The cardinal points coincide with the HPI coils Compare the digitized distances of the coils with the actual values to verify correct digitizer operation Put the phantom into the sensor helmet of the probe
16. of this channel Used for bipolar channels together with Test Osc input Leave off when testing unipolar channels Test Osc must be also on see below to use the test signal Set to Off Common parameters Ref Source Select reference electrode Wilson Central Terminal WCT computed average of unipolar channels 1 3 or isolated signal ground of the preamplifiers Set to Reference electrode normally used See Appendix for explanation of terms Ref Test Osc Connect test oscillator signal to reference electrode input Test Osc must also be on see below to use the test signal Set to Off Active ground Connect AC signal from reference electrode to isolat ed signal ground driver Set to Off NM20215A G 83 El Maintenance 8 5 84 Test Osc Test oscillator on off To use the test signal the connection to individual channel inputs see above must also be enabled Set to Off Test Osc Freq Test oscillator frequency Set to 20 Hz TestOsc Amp Testoscillator amplitude nominal value atinput assuming terminator block with 1 MQ impedance connected Select all EEG and MEG channels and start acquisition hit GO Select the EEG channel sets in the raw data display Set the EEG scale to 20 uV this may vary slightly according to local line noise level Observe the noise level Verify that there are no channels whose noise level clearly exceeds that of other channels or shows a complet
17. on the table or armrests When the patient is sitting in the chair the seat is lowered down by pushing down constantly on the release pedal The chair can then be pushed underneath the Dewar using the green handle of the chair Be careful when approaching the helmet tall patients may have to bow their head Push the chair first all the way in Lock the chair temporarily before final adjustment in place by lowering the handlebar to the lowest position close to the floor The seat is then elevated by pumping on the front pedal on the right hand side of the chair until the patient s head is covered with the helmet Keep lifting until the top of the patient s head touches the top of the helmet Inform the patient to give feedback during lifting During the measurement the subject patient s head leans against the Dewar helmet The lower parts of leg rests can be elevated to nearly horizontal position Grab the leg rest with one hand and elevate it to the upmost position The rests will lock automatically and wil be released when lifted again After the measurement release the leg rest by slightly elevating it which releases the latch Support the leg rest when lowering it down Advise the patient to lean back on the helmet and relax Adjust the position of the chair in the front back direction as needed to maximize patient s comfort Use additional pillows from the pillow set provided with the chair Comfortable position minimizes patien
18. panel Note that both reference and ground electrodes must be connected either to the headbox or to the electrode interface panel CAUTION Do not ground subject to actual ground e g the wall of the magnetically shielded room The GND terminal refers to isolated signal ground of the preamplifier connected through a current limiting driver circuit Do not place conducting parts near the subject that he she may touch while connected to the equipment The operator exits the room Close the magnetically shielded room door 4 N Ei A typical measurement with Elekta Neuromag 48 CE NOTE In case of studying patients or small children an accompanying person in the room is highly advisable particularly if it is likely that the patient cannot call for help or get out in case of emergency Audio and video monitoring is also recommended If an intercom system is installed ask the subject if the subject is ready Start the data acquisition For acquisition software release 3 3 and later an electrode impedance check window is displayed Check the imped ance levels and correct if necessary For optimum performance imped ances below 10 kQ are recommended Measure the HPI coil locations with the respect to the sensor array If the HPI fails check the leads and ask the subject to move the head in a slightly different position and try again Start stimulation if using any During the acquisition the raw data and averaged data should be
19. re evacuated which is a normal procedure during annual mainte nance Call an Elekta service representative NM20215A G 5 5 1 Gantry bed and chair Construction A NM20215A G The constructions of the gantry bed and chair are shown in Fig 5 1 The gantry comprises the base unit and the probe unit which is inside the rotating cradle The helmet shaped lower tip of the Dewar extends outside the cradle The gantry has two fixed predefined tilt angles corresponding to supine and upright measurement positions Either of the measurement positions can be chosen by using the up or down buttons and the manual latch release bar that are on the rear side of the gantry CAUTION Change of the measurement position must not be done when a patient or the chair is underneath the gantry LU Ji Figure 5 1 Upper picture Supine measurement position Lower picture Upright measurement position 57 Gantry bed and chair 5 2 58 A On both sides of the gantry there are covers under which EEG and auxiliary electronics interfaces are located The covers are opened and closed from the front of the gantry The patient bed is mobile and its wheels are provided with locks The gantry is equipped with a removable bed docking piece that is used together with the patient bed After docking the bed to the gantry and locking the wheels the lock of the upper bed can be released and the upper be
20. simplex mode with manual speech direction control by pressing the T button Then it is possible to listen to the subject but the subject can t hear what is spoken in the control room In order to give instructions to the subject press T button on the table station and speak close lt 50 cm to the device The button has to be kept down as long as you speak During that time you can t hear what the subject says When the button is released the system returns to the listening mode To close the connection press X button To return to automatic speech direction control mode close and re open the connection by pressing X and CALL 11 Figure 7 3 The intercom system For explanations see chapter 7 2 1 NM20215A G Auxiliary electronics 7 The volume of the loudspeaker to the magnetically shielded room is adjusted inside the main station For more information see the intercom instruction booklet 7 4 Video monitoring system option 7 4 1 General The schematic diagram of the closed circuit television system is shown in Fig 7 4 The camera 1 is placed inside a separate RF shield The cable 2 goes through a dedicated feedthrough to the monitor 3 The camera should be kept further than one meter away from the Elekta Neuromag in order to avoid additional noise 7 4 2 Usage The system is activated by switching on the monitor unit and the power supply for the camera It is possi
21. the accuracy of source localization Many walls floors and ceilings also contain significant amounts of metal To test whether the surroundings affects the accuracy of the readings digitize an object with known dimensions For example digitize the centers of the HPI coils permanently attached to the phantom and compare the readings with the known values see Table 2 in section 7 2 In both upright and supine measurement position make sure that prior to positioning the patient the green OK light of the position indicator display is lit For details see Section 5 2 Guide the subject in the magnetically shielded room and assist him her to the chair or on the bed If seated measurement position is used follow the instructions given in section 5 5 in supine measurement position exper iment follow the instructions given in section 5 4 Plug the head position indicator coil connector to the HPI connector on the interface panel on the left side of the gantry see Figs 1 19 and 1 20 and the eventual electrode cap and reference and ground electrodes to corresponding connectors on the electrode interface panel see Figs 1 12 and 1 13 on the right side of the gantry NOTE Instruct the patient to keep the head steady during the recording If a headbox is used connect it into the appropriate connector 1 32 or 33 64 of the electrode interface panel Connect eventual bipolar elec trodes to the appropriate terminals of the electrode
22. the handle is lowered against the floor The lower parts of leg rests can be elevated to nearly horizontal position Elevate the legrest by hand or foot to the upmost position The leg rests will lock automatically and will be released when lifted again A dedicated table is part of the system delivery Attach the table by gliding it in the guides on the side panels of the chair A pillow set is delivered with the chair Use the pillows as needed behind the subject s lower back or shoulders The chair is equipped with a safety belt that can be useful in stabilizing the subject and preventing the subject from drifting down during the measurement Subject preparations and positioning Refer to Section 3 3 for patient preparation Adjust the Dewar to the upright position as described in Section 5 3 Before placing a patient into the chair elevate the upper part of it to half of the maximum height Now it is easy for the patient to sit down into the chair For patients with limited movement capacity it is advisable to have the chair in the uppermost position For tall patients use also the shoulder support pillow Adjust the lower back support pillow as needed Fasten the seat belt firmly over the hipbone for increased stability Insert the dedicated table into its guides according to the need NM20215A G Gantry bed and chair CAUTION Be careful not to get fingers or toes between moving parts Instruct the patient to keep hands
23. the main electronics cabinet has been off due to mains failure or because of disconnecting the power from the isolation transformer for e g service operations Boot the acquisition workstation if it has not started automatically Wait until it runs normally On the mains control panel of the main electronics cabinet see Fig 6 2 ensure that the green rocker switches Preamplifiers real time comput ers main electronics are in off position Inside the MEG electronics cabinet the individual power supply units are connected to outlet socket strips located in the reare of the cabinets Ensure that the power cords are in place and that the switches of the individual power supplies are in the on position NM20215A G Electronics g 6 3 2 pH a dii ge Real time Mann DSP computers electronics p HES LT s Main switch Circuit breaker 104 Figure 6 2 The mains control panel of the main electronics cabinet Switch on the main electronics cabinet power by turning the main switch on the mains control panel The switch will automatically turn back into off position if mains voltage is too low Proceed with normal powerup instructions 6 3 2 Normal powerup Make sure that the main main switch om the mains control panel is in the 1 position After turning the main switch to 1 position wait until the ethernet switch has started up indicated by the self test and f
24. the pressure goes up further to approximately 60 kPa 0 6 bar the safety rupture membrane on the top plate breaks and Helium gas will flow though the emergency duct Should this happen or if the membrane breaks by itself plug the membrane opening with a rubber bung contained in the Cryogenic Accessory Kit after the pressure has decreased Try to identify the cause of the pressure rise and have the safety rupturing membrane replaced 5 O1 4 Cryogenics 56 The frozen silicon exhaust hose of the probe unit breaks because of thermal stresses This may be associated with a loud popping sound and a greyish cloud of gas caused by condensing moisture This may sound and look dramatic but do not panic Should this happen open the hose clamp valve at the transfer exhaust hose of the storage container and let the pressure drop Beware of the extremely cold non life supporting gas You may wish to step out of the magnetically shielded room while waiting for the pressure to drop Replace the broken silicon hose when ithas warmed up sufficiently There is a spare hose and plastic connection pieces in the Cryogenic Accessory Kit provided with the system There is not enough Helium to complete the transfer This shows up as difficulties in maintaining the pressure in the storage container and the local level indicator also stops rising If the transfer is far from complete get a new storage container and start again Dry the ins
25. the system 1 NM20215A G 2 a 2 2 B 2 V A V D00000 REF GND Fig 1 15 The electrode headbox for 32 unipolar channels and reference and ground electrodes Cable separate not shown are available upon request from Elekta Neuromag Oy Alternatively separate electrodes can be connected into a headbox see Fig 1 15 Using the electrode cap or headbox the subject can be conveniently prepared outside of the shielded room and the cap or headbox plugged in the electrode interface panel when the actual measurement starts 21 a1 Overview of the systen 1 9 22 EEG electronics The preamplifier unit is located inside the gantry It is fully software controlled and it does not contain any switches connectors or other parts the operator needs to access The first 60 channels are always unipolar single ended using common reference from reference electrode and channels 61 64 are bipolar differential Differential channels can be used e g to measure bipolar electrocardiographic ECG electromyographic EMG electro oculo graphic EOG signals Channels 61 64 are optionally configurable as unipolar single ended This however requires corresponding hard ware cabling in the electrode interface Optionally the number of channels can be inreased up to 128 Each additional group of 32 channels has 28 unipolar channels and 4 hardware configurable uni bipolar chan nels For each ch
26. using the green handle 64 NM20215A G 6 Electronics 6 1 Precautions A A y OAS 6 2 General 6 2 1 A 6 2 3 NM20215A G CAUTION For precautions concerning electrical safety and artefact free operation refer to chapter 2 2 NOTE The electronics contains components susceptible to static electricity Read precautions of chapter 2 6 2 first Rack installation CAUTION The electronics is designed to be operated in proper RF shielded cabinet mounting only Do not disconnect any cables In particular the unit must be operated with cooling fan units on Their cables must not be disconnected The main electronics cabinet comprises two MEG subracks one EEG subracks and an MEG preamplifier power supply The mounting of the units inside the cabinets is shown schematically in Fig 6 1 Electronics control Normal operation of the electronics requires no user action except power up and shutdown All settings of the electronics are computer controlled Pre defined settings for proper SQUID working points are automatically loaded to electronics at power up For further details refer to Sensor Tuner User s Guide and Data Acquisition User s Guide Power supplies CAUTION There are no operator serviceable parts inside the power supply units Do not open the covers The main electronics subracks have several power supply units isolated EEG Power Supply Isolated power supply for EE
27. 10 mA constant current through each electrode simultaneously using a graphite cathode connected to the negative terminal of a power supply and the electrode leads connected to the positive terminal A good Ag AgCI coating is usually formed in about 5 minutes Rinse the electrodes thoroughly in water 8 9 Annual maintenance NM20215A G The annual maintenance service must be left for trained service person nel The service includes e Overall system performance test noise phantom measurement e Identifying causes of unresolved reported problems e Checking of magnetically shielded room grounding installations door mechanisms etc Checking and cleaning of the Dewar boiloff rate e Re evacuating the Dewar vacuum if necessary Performing detrapping if necessary Checking of siphons re evacuating if necessary e Checking the mechanisms of the gantry including the rope replacing worn out parts lubricating mechanisms if necessary and cleaning the unit The ropes are changed every five years e Checking the bed and chair mechanisms and cleaning both of them top up of the hydraulic liquid of the chair and inspection for leaks 8 Maintenance Checking the feedthrough filter unit the electronics cabinet and the data acquisition system cabinet including checking all cabling and replacement of dust filters if necessary Checking of grounding and isolation arrangements Cleaning Checking workstations and peripherals inc
28. EEG pre amplifier unit is floating Internally the preamplifiers see all signals with respect to GNDi Tech nically speaking isolated ground refers to the center tap of the secondary of the safety isolating transformer of the EEG preamplifiers Because of safety principles isolated ground should never be connected directly to humans see below In the headbox and electrode caps supplied with the system or available as options isolated ground is not accessible EEG reference NM20215A G Signal subtracted from all the single ended channels In normal EEG measurements the reference signal is derived from the reference elec trode For ECG measurements the Wilson Central Terminal WCT see below reference can be used For testing and calibrating the EEG system 91 A Appendix 92 the reference signal can be connected to the isolated ground of the preamplifiers The source of the reference signal can be selected by using the Squiddler EEG utility program EEG reference electrode An electrode placed usually at an inactive area monitoring the potential of the subject This can serve for two purposes depending on the mode of the preamplifier 1 it gives the signal reference which is subtracted from the single ended EEG channels when selected as the reference source and 2 it acts as a sensor for the active ground driver Because of 2 the reference electrode has to be connected even when using only diff
29. Elekta Neuromag Elekta Neuromag System Hardware User s Manual Revision G September 2005 ELEKTA Copyright Elekta Neuromag Oy Helsinki Finland 2005 This document contains copyrighted and possibly confidential information and is intended for the exclusive use of customers having Elekta Neuromag products and authorized representatives of Elekta Neuromag Oy Disclosure to others or other use is strictly prohibited without the express written authorization of Elekta Neuromag Oy Elekta Neuromag Oy reserves the right to make changes in the specifications or data shown herein at any time without notice or obligation Elekta Neuromag Oy denies any responsibility for damage to apparatus or persons due to improper use or service performed by unauthorized persons Elekta Neuromag Oy assumes no liability for damage and or failure of equipment caused by faulty site preparation Elekta Neuromag is a trademark of Elekta The system has been marketed and sold previously under the name Neuromag Vectorview also a trademark of Elekta All other company names and product names are used for identification purposes only and they may be trademarks or registered trademarks of their respective owners All rights reserved Reproduction in any form without the written permission of Elekta Neuromag Oy is strictly prohibited Printing history Neuromag p n Date First edition NM20215 4A 15 5 1998 First revised edition NM20215 4A 1 22 5 1998 S
30. G amplifiers is located in the feedthrough unit t is powered by a 24V transformer in the preamplifier power supply unit inside the main electronics cabinet Q gl g Electronics 6 3 66 MEG main a Main electronics f il et electronics rack 1 H P al ql power Alt aa PER supplies fi aana COUT MEG aka i PP 1i ji cables H nili y i ili ie Ii ieee EEG main AR d socket electronics H E A Strips rack ill E all ee Pree CL EEG nang FE inal ah Sa ea a hy rs EL K cables i Preamplifier power supply Ethernet switch VME data acquisition rack Mains m control 3 ae pang a T socket strip FRONT BACK Figure 6 1 Mounting of the electronics units inside the main electronics cabinet Left front view right back view Powerup and shutdown instructions 6 3 1 pu Cold start powerup after mains failure NOTE The main electronics cabinet has been equipped with a power failure release main switch to ensure proper boot up sequence of the computers Please follow these instructions after the mains power com ing to
31. Helium refills the gas exiting from Dewar may be extremely cold Skin contact with the exhaust line tubings should then be avoided The Helium space of the Dewar is vented to prevent buildup of pressure due to evaporating liquid Helium The outflowing gas is directed via an exhaust line provided with a backlash valve to open air outside the building or to gas recovery system if applicable The dedicated exhaust line together with the sealing of the He space of the Dewar prevent cryopumping of other gases from the atmosphere The top flange is equipped with pressure relief valve and a rupturing membrane which will let gas out should the pressure inside the Dewar rise for some reason Also a pressure gauge is attached on the top flange The pressure relief system which is based on rupturing membrane vents via a separate safety exhaust duct to outside of the building The gantry is designed to keep the Dewar in proper position CAUTION The structural integrity of the Dewar should not be damaged in any way Absolutely no holes may be drilled to the Dewar e Hard shocks to the Dewar must be avoided CAUTION The Dewar vacuum must not be opened to atmospheric pressure under any circumstances The Dewar is equipped with a vacuum lock valve and is sealed by means of a blind flange to prevent accidental opening and leakage NM20215A G 29 Safety instructions and precautions 30 A through the vacuum lock
32. QUID electronics 1 7 SQUID electronics The SQUID electronics unit is used for reading out and amplifying the electrical signals from the SQUIDs The electronics boards include preamplifiers for SQUID readout inside the probe unit and main boards containing analog todigital A D converters digital to analog D A converters and a digital signal processor for feedback loop as well as adjustable digital anti aliasing low pass and high pass filters see Fig 1 11 The main boards reside inside the main electronics cabinet The boards are connected to the real time data acquisition computers for control and for data forwarding Radio frequency interference shielding of the SQUID electronics is provided using the filter unit which is an appropriate cabinet outside the magnetically shielded room with feedthrough filters for all cables and isolation of power lines The signal cables between the preamplifier boards on the top plate of the Dewar and the filter unit go through two feedthrough tubes of the shielded room The data acquisition system includes a dedicated optic link from the real time data acquisition computer for controlling the preamplifiers Fore block and schematic diagrams of the electronics refer to Elekta Neuromag System Hardware Technical Manual 1 8 EEG electrode interface NM20215A G The electrode interface is located in the gantry side panel To access it raise the side panel cover until it locks The interface pa
33. a a back flow valve or a sufficiently long and narrow exhaust tube Do not leave the fixed L siphon at the top of the Dewar open Block the opening with the dedicated plug when not transferring Helium Do not leave the boil off tube vent directly into the room Use silicon hose to lead the exhaust vent out from the magnetically shielded room If the hose breaks during transfer replace it with a new hose as soon as possible Do not remove the fixed siphon or the boil off tube from the top plate The openings must be plugged with rubber bungs provided in the Cryogenic Accessory Kit if the fixed siphon or the boil off tube are ever removed even for a short while If the safety exhaust rupture membrane accidentally breaks the opening must be plugged with a large rubber bung and the membrane replaced provided in the Cryogenic Accessory Kit 2 2 Electrical safety 2 2 1 NM20215A G All Elekta Neuromag SQUID sensor electronics is operated using low voltage max 15 V5 24 V power supplies connected to the mains through an isolation transformer To avoid electrical interference most parts are shielded and grounded class I according to IEC 60601 1 The probe unit is operated inside a magnetically shielded room to avoid electromagnetic interference Subject connections All applied parts of MEG equipment connected to the subject are made of electrically insulating materials only They are classified as BF body floating type
34. according to IEC 60601 1 Helmet shaped sensor assembly is located inside a double walled isolat ing fiber reinforced plastic vacuum gap Dewar vessel making no electrical contact to the subject The device does not generate radiation During the experiment it is not possible for the subject to get in contact with grounded parts 32 Safety instructions and precautions be D 2 2 2 gt gt Head position coils on small printed circuit boards are spiral shaped The coils are connected to isolated leads and cast with isolating epoxy No electrical contact to the subject is thus made Current fed to coils is typ 70 uA and the resulting field less than 1 nT The EEG subsystem contains an applied part of BF type body floating in galvanic contact with the subject The applied part has been carefully designed and built to fulfill the safety regulations as set by international standards IEC60601 1 and IEC60601 2 The EEG preamplifiers are optically isolated and the power supply of the EEG preamplifiers is provided with safety isolation transformer CAUTION To eliminate any risk of electrical shock hazard the EEG subsystem must be properly installed by authorized service personnel and used as part of the Elekta Neuromag system according to manuals and assembly instructions Internal cabling must not be changed NOTE The EEG subsystem cannot be used as a standalone unit outside of the magnetically shielded room T
35. ail indicators going off Bootup takes about one minute Switch on the real time computers from the mains control panel Switch on the Main DSP electronics from the mains control panel Wait until all electronics boards show steady green run lights and the fail lights are off Boot up takes about 30 60 seconds If the bootup fails open the back door of the main electronics cabinet and check the indicator LEDs of individual power supplies see Fig 6 3 Switch on the Preamplifiers from the mains control panel Run Restart acquisition programs by double clicking its icon in the Maintenance toolbox on the acquisition workstation NOTE Each time the MEG front end is powered it must be initialized either by invoking the restart acquisition programs as above or by invoking the Squiddler utility program and issuing the initialize electron ics command immediately after all voltages are on Failing to do the initialization can lead to increased liquid helium boiloff rate resulting in substantially shortened refill interval NOTE For optimum noise performance let the preamplifiers stabilize for approximately two hours before commencing MEG measurements Keep the preamplifier power supply normally always on NM20215A G 4 6 Electronics Ci 6 3 3 BH NOTE individual main electronics power supply units will not start up if any of their indicator LEDs on the back see Fig 6 3 is lit Thi
36. all indicators will be dark If the internal temperature of the low voltage side exceeds the limit marked on the cover secondary the unit will turn off all its output voltages and the indicator LED for the temperature will turn red If a secondary thermal shutdown occurs wait at least 30 minutes to cool down the unit Check that the fans operate normally Try restarting the unit by detaching its power cord wait unit the red indicator LED goes off and re connect the power cord During startup all indicators are lit briefly in a sequence first green and then red If the problem persists or repeats often call a service representative If the transformer primary thermal shutdown occurs disconnect the power cord of the unit and wait at least 30 minutes to cool down the unit The primary winding thermal switch will reset automatically Try restart ing the unit by reconnecting its power cord If the problem repeats call a service representative CAUTION Overheating is normally a symptom of a fault To reduce risk of fire the reason must be resolved Cooling fans BH The cooling airflow in the cabinet enters through a dust filter below the cabinet floor and exits throgh the top of the cabinet In addition there are individual local fan units connected to mains supply so that they operate simlutaneuosly with the unit they are cooling Power cords of these fan units must not be removed or replaced NOTE For proper airflow in the
37. annel the gain and high pass frequency can be set individu ally Adc mode is also provided with a possibility for offset compensation Unused channels can be deactivated by software eliminating the need of grounding jumpers in input A built in test oscillator with selectable amplitude and frequency can also be connected by software individually for each channel The interface of the channel control is explained in Section 8 4 For potential equalization between the isolated preamplifier and the patient it is necessary to connect the patient to the isolated signal ground of the preamplifier over a ground GND electrode However to limit the patient current to a safe level the preamplifier signal ground connection is provided through a current limited ground driver connected to the GND terminal of the electrode interface panel The reference REF electrode is internally buffered and is normally selected as the common reference for all the single ended channels To facilitate common mode disturbance rejection e g to reduce line frequency ripple and drifts the reference electrode can also be connected as ac input to the ground driver circuit to provide potential equalization between patient and preamplifier signal ground so called active grounding effective only above 5 Hz During measurements both reference and ground elec trodes must be connected The place of the ground electrode is not critical typically it is placed to some inactive
38. aporation 20 9 kJ kg 2 6 kJ liter One liter liquid corresponds to approx 750 liters of gas 20 C 101 3 kPa Skin contact with liquid or cold gas or cooled objects may cause severe frostbite Flow of cold Helium gas makes a very good thermal contact with any surface it passes by unprotected skin cools below freezing point in seconds Dangerous pressures may arise as a result of rapid vaporization inside closed vessels NM20215A G Safety instructions and precautions A A A e Liquid Helium can cryopump other gases such as nitrogen oxygen water vapor etc which at liquid Helium temperature solidify This may lead to blocking of the vents and consequently buildup of dangerous pressures in cryogenic vessels See Sect 4 1 2 Structural safety The Dewar has a good thermal insulation to minimize He boil off The insulating vacuum is properly sealed and all parts are fabricated leak tight Because of the thermal insulation all parts of the Dewar that may come into contact with the user remain at room temperature at all times during normal operation The cooling capacity of the evaporating cold Helium gas is employed to partly minimize the unavoidable heat leak from room temperature to the cryogenic temperature Therefore under operating conditions the outflowing exhaust gas is warmed up to essentially room temper ature before leaving the Dewar However during increased outflow occurring normally only during liquid
39. ar causes large irregular low frequency drifts to MEG signals because oxygen in its solid form is very paramagnetic Because of the above all vessels containing liquid Helium must be sealed from the atmosphere and properly vented via a back flow valve or a sufficiently long and narrow exhaust tube Flow of cold Helium gas makes a very good thermal contact with any surface it passes by unprotected skin cools below freezing point in seconds Even after warming up to room temperature the odorless and colorless gas may cause a risk of suffocation if ventilation is not taken care of Breathing Helium gas does not bring about any physiological unpleasent symptoms before dizziness The pitch of the voice of the person charac teristicaly raises when a large fraction of air is replaced with Helium gas 4 Cryogenics 4 2 4 3 50 You should avoid using magnetic tools and electrical equipment like hot air guns inside the magnetically shielded room If absolutely necessary they must be kept more than one 1 meter away from the sensor array For sensor detrapping see 2 4 2 Refill schedule The recommended liquid Helium refill interval of Elekta Neuromag is 7 days It is recommended that a fixed weekly schedule is set up for Helium transfer In addition to the person responsible for the transfer backup personnel should be assigned It is highly advisable to monitor the Helium level regularly to avoid accidental warming up of the sys
40. are vented through their proper return lines and all the other valves are closed Remember to switch off the local liquid Helium level display NOTE In installations where the siphon precooling line has been left out let He exhaust first into the atmosphere through the flexible siphon Then connect the tip of the flexible siphon to the fixed siphon as in 11 above and continue slowly as in 12 Adequate ventilation of magnetically shielded room must be provided cf Sect 2 1 2 and 4 1 4 5 Troubleshooting transfer problems A NM20215A G Use caution and care when handling the Helium storage containers One liter of liquid Helium corresponds to approximately 750 liters of NTP Normal Temperature and Pressure Helium gas Cold Helium may cause frost bites and it may replace breathing air However there is no need to be alarmed when liquid Helium is properly handled CAUTION Beware of the extremely cold non life supporting gas The following hints may help you in solving problems which may arise during a transfer The pressure in the probe unit of the Elekta Neuromag goes high Release the hose clamp valve blocking the transfer exhaust hose If the pressure still keeps increasing open the relief valve on the storage container and the siphon precooling valve Watch out for the even tual stream of extremely cold gas The relief valve of the probe unit will open when the pressure inside the Dewar is 10 kPa 0 1 bar If
41. area like on the cheek If the reference and ground electrodes are left out common mode potential of the subject with respect to the preamplifier common potential may saturate the amplifiers The feedthrough unit isolates the EEG front end from the data acquisition system with optocouplers i e there is no galvanic contact to the rest of the electronics The feedthrough unit also eliminates RF interference from the data acquisition system NM20215A G Overview of the system El The feedthrough unit also houses the isolated power supply for the electrically floating front end and a control board for setting the pream plifier parameters The modules in the feedthrough unit do not contain any parts the operator needs to access nor are there any adjustable parameters The EEG data acquisition contains Signal Acquisition boards SAM with analog to digital converters and signal processors for filtering etc on line operations The boards are connected to the real time data acquisition computers for control and for data forwarding All A D conversions are started simultaneously synchronized with MEG chan nels and the sampling rate is the same as in MEG channels The data acquisition system includes a dedicated optic link from the real time data acquisition computer for controlling the preamplifiers For block and schematic diagrams refer to Elekta Neuromag System Hardware Technical Manual 1 10 Auxiliary electronics NM20215A G
42. arts Follow the pressure indicated by the gauge on top of the probe unit of the Elekta Neuromag the pressure should stay lower than 0 1 bar 10 kPa If necessary you can lower the pressure by letting gas out of the storage container through the transfer exhaust hose In a few minutes the siphon cools down sufficiently This is indicated by heavy frost on the precooling line on the gantry Release the plastic hose clamp valve and wait for the pressure to go down Use thick protective gloves and beware of the cold Helium flowing out Close the valve on the precooling socket Loosen the knurled sleeve nut holding the siphon in place Leave the siphon in the precooling socket Loosen the plug at the input of the siphon fixed to the probe unit of the Elekta Neuromag Replace the plug as quickly as possible with the tip of the siphon During the short interval when the fixed siphon on the probe unit is unplugged there should be Helium flowing out of the fixed siphon as well as from the flexible siphon If this is not the case there might be a plug of frozen air in the siphon see Section 4 5 Secure the siphon in place by tightening the knurled sleeve nut on the siphon Place the plug of the fixed siphon to a place where it is readily available e g the plug holder at the cover of the refill opening or the precooling socket Block the transfer balloon exhaust hose with the plastic clamp again and pump gently with the rubber balloon Follow the p
43. as rotated into the uppermost position and the movement stops This is also indicated by the amber Limit light Do not stop the movement unnecessarily by releasing the up button Figure 5 3 Lifting mechanism control buttons NM20215A G 59 3 Gantry bed and chair 60 pom Figure 5 4 The latch release bar Press the down button until the dewar stops over the latches The movement is very short Now the weight of the dewar is carried by two locking latches A green OK light on position indicator is led to show that the system is ready for use All other lights on the indicator display should be off Wait a few minutes for stabilization before starting measurements 5 3 2 Changing the position from upright position to supine posi tion Remove the chair from the gantry and make sure that no one is underneath the dewar during position change Press the up button located in the back cover of the gantry until the movement of the dewar stops and the amber Limit light is lit The Tension indicator is also on but OK indicator is off The move ment is very short Grab the greenlatch release bar on the back of the gantry see Fig 5 4 and pull it down This will disable the locking latches of the dewar Press the down button and keep it pressed while you keep the bar down After the dewar has rotated downwards and passed the latch position you can release your hand from the bar without releasi
44. bed unlocked and is pulled off the gantry Lock the upper bed again Alternatively when head support is not used the bed is first pushed against the gantry with patient s head on bed and docked Only after that the patient s head is slid into the helmet During the measurement the patient s head leans against the Dewar helmet After the measurement the patient s upper part of the body is first pulled out of the helmet and the head supported onto the bed If the bed is moved after the measurement release the locks of the wheels Move the bed using the green handle 5 5 Positioning the patient in seated position 5 5 1 NM20215A G Construction of the chair Construction of the chair is shown in Fig 5 6 The height of the seat of the chair is adjusted using the pedals which are on the side of the chair To elevate the seat pump the elevation pedal which is on frontal part of 61 Gantry bed and chair 62 5 5 2 Table Latch Handle Le ee Ed TT Lifting pedal Release pedal Figure 5 6 Construction of the chair the side to slide the seat downwards push constantly the release pedal on the rear part of the side NOTE Do not use force or stand on the elevation pedal after the maximum height of the seat is reached The pedal might break The chair can be moved using the green handle The handle locks into its uppermost position A break that prevents the chair from moving is activated when
45. ble to connect two cameras tothe monitor unit Anyhow one must keep in mind that the cameras inside the MSR have to be provided with RF protection housing The MSR camera is connected to the input 1 It is selected by pressing the camera 1 button on the front panel of the monitor unit For more information see the CCTV instruction booklet 7 5 Audio electronics NM20215A G The connection of the audio electronics in the gantry side panel is shown in Fig 1 20 of Section 1 10 The electronics has audio output connectors for the patient s and optionally for the assistant s non magnetic ear phones The system also includes a microphone input connector and a microphone for the optional intercom unit Figure 7 4 The video monitor system For explanations see text 79 Fa Auxiliary electronics 7 6 Analog input Eightanalog inputs standard optionall 16 with the 128 channel EEG expansion for miscellanaous analog signals 10 V are available in the main electronics cabinet The inputs are connected to a parallel D25 multipole connectors 1 connector 8 channels at the back of the main EEG rack A fanout box for eight BNC connectors is also provided The pinout for the parallel connectors is shown in Fig 7 5 13 FRONT VIEW 1 O oo00000000000 O 000000000000 25 14 1 Input 1 5 Input 5 14 Ground 1 18 Ground 5 2 Input 2 6 Input 6 15 Ground 2 19 Ground 6 3 Input 3 7 Input 7 16 Ground 3 20 Ground 7 4 I
46. cally shielded room Care must be exercised to avoid contact of conducting parts of the electrodes including REF and GND electrodes to ground or other conducting parts which may be grounded or become live at mains voltage Do not ground subject to actual ground e g the wall of the magnetically shielded room Do not place conducting grounded objects near the subject that he she may touch while connected to the equipment Auxiliary user supplied equipment To avoid risk of electrical shock equipment supplied by the user and connected to humans must comply with isolation requirements similar to or better than this system For connection of these devices isolated and filtered power outlets are provided in the stimulus cabinet Maximum current available is 10 A total CAUTION The applied parts of user supplied equipment must be of BF or CF type cardiac floating and they must fulfill the norms according to IEC 60601 1 for medical electrical equipment Although the individual devices fulfill the leakage current requirements set forth in standards a possible hazard exists caused by the summation of leakage currents when several pieces of equipment are interconnected Also other equipment connected to the same stimulus trigger interface unit must fulfill the requirements of IEC 60601 1 NM20215A G Safety instructions and precautions 2 2 2 4 Li The power outlets in the electronics and stimulator cabinets connected to the
47. chapter Attaching single electrodes Instead of the electrode cap single electrodes can be used especially if only a few are required In addition single electrodes are used for bipolar channels and for the reference and ground electrodes also when electrode cap is employed NM20215A G A typical measurement with Elekta Neuromag E 3 3 4 NM20215A G The reference electrode acts as a reference for all the unipolar channels of the cap and the ground electrode is used to set the subject to common potential with the preamplifiers to reduce common mode interference Line frequency ripple and drift may be further reduced by using active grounding as described in Chapter 1 9 Both the reference and ground electrodes must be connected Place the reference electrode according to the electrode derivation used The place of the ground electrode is not critical typically it is placed to some inactive area like cheek In SEF measurements place the ground electrode close to the stimulating electrode to minimize artifacts Prepare the skin with an abrasive skin cleaner such as OmniPrep Skin Preparation D O Weaver amp Co Aurora CO USA or with alcohol using a cotton swab Apply electrode paste e g Grass EC2 Grass Instruments Quincy MA USA to the electrode and put it in place Press the electrode with a small piece of paper tissue until the paste is hard enough to keep the electrode in place Special adhesive washers s
48. d can be moved in horizontal direction The patient chair is provided with wheels The green handle can be used to position the chair underneath the Dewar After adjusting the position of the chair an elevation pedal on the side of the chair is pumped to elevate the seat The seat can be lowered by pushing the release pedal down CAUTION Care should be excercised to prevent limbs being left between moving parts of the chair or bed and gantry or doorway Position indicator display The operation of the gantry lifting mechanism can be monitored with the help of the position indicator display located on the wall behind the gantry see Fig 5 2 Indicators of the display are the following Green light OK Gantry position is secured supine or seated This is normal position Never place a subject under the gantry except when green OK light is lit Amber light Tension Gantry position is not secured and weight of the dewar cradle tensions the ropes of the lifting mechanism This is normal during up down movement When tension of the ropes is released and light goes off downward movement of the motor stops Amber light Limit Dewar cradle has reached the upper limit of the upward movement and motor stops Only downward movement is possible This is normal during up down movement Red light Fault Abnormal condition due to malfunctioning of the lifting mechanism and or the fiber optic sensors monitoring the
49. d room should be controlled according to Elekta Neuromag Site Planning Guide It is recommended that the user is warned about magnetic objects and devices with a sign posted at the entrance of the magnetically shielded room see Fig 2 2 The electrodes and electrode caps should be stored carefully preferably hanging in dry room air Do not keep the electrodes and the caps on a table where they might be contaminated with magnetic particles Wash them carefully after each use see cleaning instructions in Chapter 8 7 NOTE The connectors used in the headbox may contain a thin interme tallic layer of magnetic material To avoid magnetic artefacts during MEG measurements do not bring the headbox close to the helmet and Keep it steady Put it on the bed or on the removable table of the chair at least 0 5 m away from the helmet Do not put it in the subject s lap or on the chest as movement caused by respiration may produce an artefact 37 A Safety instructions and precautions 2 5 38 2 4 2 Detrapping The Elekta Neuromag triple sensors are equipped with heaters To detrap a sensor invoke Tuner program from the Tools Menu of the Data acquisition program Then activate the heater from the tuner program You can heat any sensor element three channels at a time or all sensor elements sequentially heat all command Detrapping all channels takes about one minute Measure the noise level of the sensor and if nec
50. dentia 2 2 Electrical Safety RSR nette tin eae 2 2 1 Subject connections ere 2 2 2 Power supplies and grounding cccceescccereeeeeeeeereeteeeeeeees 2 2 3 Auxiliary user supplied equipment 2 0 4 Defibrillators Lara miennes his 2 3 Mechanical Satety ici fus tt Me the die eme 2 4 Trapped flux in the sensors 2 4 1 Preventive measures 2 4 2 Detrapping 2 5 EEG Electrodes CCLEEELECEEEEEEE ESS CCECCE ETES ECTS CEE EEE EEE ETES EEE EEE CEE EEE EE EEE EEE EC EEE EEE 2 6 Electromagnetic Compatibility 2 0 0 0 cccccesssseeeeeeeeeeeeeeeeseseesseesnsaaeeeeeeeeeess 2 6 1 Electromagnetic interference ccceecccccecssssceeteeesseseeenseees 2 6 2 Electrostatic discharges 0 cece cessneeeeeeeesesteeeesssssseeeeeees 2 7 Other BIECAUNONS Lennon NA nes ts NM20215A G 3 1 3 3 5 6 6 1 6 2 6 3 A typical measurement with the system 41 PRIM MMAN OSs Re te Nm DT A ne a Rata 41 Pr exXperiment measures arsenal nine etapes 41 Preparation of the subject ss 42 3 3 1 Attaching the head position indicator coils 0 0 0 e eee 43 3 3 2 Attaching the electrode cap 44 3 3 3 Attaching single electrodes 44 3 3 4 Digitization of head position indicator coils c eee 45 FOC OMI e eneinio names ie a ie ouate 47 Cryogenics 49 PGC AUN ONS ger ER Ne ste den ia
51. direct contact with the person being investigated with the system and the type plate are marked with this symbol to indicate that they fulfill the leakage current requirements of the safety standard IEC 60601 1 Alternating current power line symbol On power line symbol Off power line symbol Protective ground earth terminal symbol Used to identify terminals which are intended for connection to an external protective conductor for protection against electrical shock in case of a fault or to the terminal of a protective ground earth electrode Static electricity symbol The parts of the system marked with this symbol indicate the presence of components susceptible to static electricity and require the use of special static electricity preventing techniques See Elekta Neuromag System Hardware User s Manual Magnetic objects and devices symbol The use of these symbols in the vicinity of the probe unit indicate that magnetic objects or devices may cause disturbances in the operation of the system they should therefore be avoided Non ionizing radiation RF transmitter Marking on equipment or equipment parts that include RF transmitters or that intentionally apply RF electromagnetic energy Separate collection of waste electrical and electronics equipment WEEE necessary European Union directive 2002 96 EC on WEEE Date of manufacture year four digits followed by month NM20215A G 1 Overview of the syste
52. dure the trapped flux is removed by increasing the temperature above superconductive transition temperature using heaters mounted on each triple sensor element In order to minimize the delay due to the flux detrapping in a measurement certain precautions should be noticed Preventive measures The only way of avoiding trapped flux is to avoid bringing permanently magnetized objects in the vicinity of the Dewar Therefore e Items unnecessary for the measurement should be removed hairpins jewelry eyeglasses etc e Test the objects worn by the subject particularly on the head like electrodes before the subject goes under the Dewar In particular test a new batch of electrodes before they are taken into use e To test whether an object is magnetic or not First test whether the object attaches to an ordinary bar magnet If it does the object is magnetic and it should absolutely be kept out of the magnetically shielded room If the object is not attracted to the bar magnet do a test with the Elekta Neuromag system Ask for someone to assist you in the test First carefully remove everything possibly magnetic from your pockets wrist watch belt eyeglasses etc Go with the object to be tested inside the magnetically shielded room and close the door Ask the assisting person to start acquisition of data and watch the raw data display as described in the Data Acquisition User s Guide Wave your bare hand under the magnetometer helmet
53. econd edition NM20215 4A 2 20 11 1998 Third edition NM20215 4A 3 23 11 1998 Fourth edition Rev D NM20215A D 10 6 1999 Fifth edition Rev E NM20215A E 7 7 1999 Sixth edition Rev F NM20215A F 28 2 2005 Seventh edition Rev G NM20215A G 29 6 2005 errata included in text NM20215A G 1 9 2005 2 NM20215A G Contents List of symbols 1 Overview of the system 1 1 Intended US lar naiara araia iiaa iae a a Ghat a aaa 1 2 General INformations esee e e E e E A re 1 3 Main system COMPONENTS ccccscccccccsecesessssronsccccecsssessessesssnsccsonsosnseseceosenees 1 4 TENE PODS UNIL 55 eue sed nan ir nu Ea aaia apa ea nine ent ARR 1 5 Channel layout ss ois eeina ier iaae E aa A EEE E needed 1 6 Gantry bed and CHIN iesnas a A e e A SEE ENRE 1 7 SQUID ClOCtrOMiCs Se a e oaoa eet eae 1 8 EEG electrode interface h aa a A A EA E E E ed 149 _EEG ele tronits smart 1 10 AUKINary electroniCS sis ns ss din ed ii t ep n done 1 11 Interface to stimulus electronics 0 0 cece cette eteetetessrteneeeeeeeeeeeteeneeseeees 1 12 Data acquisition System Se ts EE rate a dre 1 13 CCOMPUIEr SVSLONT 5 hentai nee ie asp tod edona tanas 1 14 Cryogenic equipment sieccie dats ccccetoudecacpentaisttaraatvcencdea nan ends cntetres 2 Safety instructions and precautions 2 1 Use OF liquid TSUN sensan sepr ienser ae shi sete saa R 2 1 1 Properties Of Hellum aniria aian 2 1 2 Stractural Safety innar ar aE EE eS 2 1 3 CIVODUMPINQ nana Ro
54. ection 5 3 Log in the computer and start the measurement session as described in the Data Acquisition User s Manual Check the liquid Helium level from computer if needed If applicable set up the stimulation equipment for the particular experiment and test the stimuli NOTE To prevent incorrect interpretation of measurement results it is important to verify that physical stimuli and their planned trigger line assignments match e g there are no swaps or mixups Set up appropriate values for the acquisition parameters like sampling rates passbands etc on the acquisition program Enter the subject data and experiment data Set up on line averaging if applicable The active MEG and EEG channels and the sampling rate as well as the low pass filter are selected from the acquisition setup dialog MEG and EEG signals are recorded synchronously using the same low pass and sampling rate settings The acquisition program also controls digital high pass filtering of MEG signals However for EEG signals the high pass 41 3 3 42 A typical measurement with Elekta Neuromag filter is analog and realized in the preamplifier The EEG preamplifier parameters like gain and analog high pass filter are initially set to their site configurable defaults values If necessary they can be controlled using the Squiddler EEG utility program described in Section 8 4 The gain and high pass filter of each channel can be set separately and da
55. ely flat line Note that the apparently excessive line frequency interference seen in this step is due to high electrode impedance 1 M Q in actual measurements with typical electrode impedances of 5 10 KQ it will be much smaller Enable the test signals from the built in signal generator in the Squiddler EEG control click the ALL button then click Test Osc input and finally Test Osc On Set the EEG scale of the raw data display to 300 uV Verify that there is a clean sinusoidal wave of equal amplitude on all EEG channels Every other channel should be 180 degrees out of phase the test signal feed is inverted not the input The amplitude of the differential channels can be different from that of the single ended channels If necessary record a short period of test signal and verify that amplitude is same for all channels using e g the signal processor program Note that the internal test oscillator is intended only for routine qualitative calibra tion checking accurate calibration is performed according to calibration procedure EL20868Y carried out by an authorized service engineer Troubleshooting Try to remove the problem by simplifying the setup until the problem has been identified Especially try to determine which issues have changed since the last time the system operated without a trouble Possible quite common causes of artefacts noisy and flat channels are e g Improper grounding of stimulators or oth
56. er peripherals causing currents to flow in the walls of the magnetic shield stimulus artefacts line interference computer data transfer artefacts Check that grounding is single point Consult Elekta Neuromag s representative if in doubt how to connect the equipment e Multiple grounding points because of improperly added equipment line interference Check that grounding is from a single point only NM20215A G Maintenance g RF interference from external sources caused by extra unfiltered cables drawn into the magnetically shielded room increased noise level shifts Check all the leads inside the magnetically shielded room Check that the cables are RF filtered properly Active digital equipment in stimulus cabinet inducing interference to leads going inside the MSR Shield the digital device or preferably have it outside the stimulus cabinet and feed the signals through a feedthrough filter Stimulus cables improperly connected stimuli not coming artefacts line interference or RF interference Check cabling Incorrect tuning noise some channels saturated Tune Too low liquid Helium level noisy channels saturated channels Transfer Helium Magnetic contamination on the subject big artefacts Remove sub ject and check with empty room Check subject and try to demag netize In the worst case magnetic objects near the sensor array lead to trapping of flux in the sensor
57. er place than the main grounding point This is very important since otherwise ground loops will be formed resulting in artefacts in the measurements The grounding system of Elekta Neuromag has been carefully designed and realized Do not add any equipment to the system or change any cabling without considering the possible side effects If in any doubt contact Elekta Neuromag The applied part of EEG is electrically floating i e isolated from ground It must not be grounded in any circumstances For potential equalization between the isolated preamplifier and the patient it is necessary to connect the patient to the isolated signal ground of the preamplifier For that purpose a terminal labelled GND is available in the electrode interface panel To limit the patient current flowing through that terminal to a safe level the preamplifier signal ground connection is provided through a current limited ground driver of the preamplifier see chapter 1 9 and Appendix The isolated preamplifier signal ground is not directly accessible when headboxes and electrode caps supplied with the system or available as options are used The isolated preamplifier signal ground which is only available internally must not be connected directly to humans as the maximum allowable current may be exceeded in a fault condition CAUTION Do not connect any of the electrode inputs of the side panel or the headbox to actual ground e g the wall of the magneti
58. erential EEG channels with the active ground switched on EEG unipolar channels Single ended channels Channels with just one electrode per channel and sharing acommon reference signal The reference signal can come from various sources see EEG reference EEG channels 1 60 are all single ended EEG Wilson central terminal WCT Average of limb electrode potentials When Wilson central terminal is selected as reference the average of the signals of the channels EEG1 EEG3 is subtracted from all the single ended channels This mode is used only in some ECG measurements when electrodes EEG1 EEG3 are attached to limbs Gradiometer A flux transformer coupling external magnetic signal to the SQUID detector making the SQUID to respond to spatial variations of the external magnetic field A gradiometer comprises a multiple pickup coil and a signal coil which couples the signal to the SQUID The gradiometer is insensitive to uniform magnetic fields IEC60601 A family of international standards concerning the safety of medical electrical equipment and systems Leakage current Current that is not functional For example patient leakage current is the unintentional current that flows from equipment via patient to ground Magnetically shielded room MSR A special enclosure whose walls floor and ceiling made of plates of high permeability alloy and of high conductivity metal typically Alu minium Typically the ma
59. erts the reading into digital form which can be transferred to the computer A local display is under the side cover of the gantry see Fig 1 19 Itis used for monitoring the liquid Helium level during Helium refilling Audio electronics interface see Fig 1 20 is provided in the auxiliary electronics panel for the delivery of auditory stimuli Two sets of head 24 NM20215A G Overview of the system 1 Fig 1 19 The auxiliary electronics panel is under the gantry side cover The liquid Helium level meter local display is mounted on the cover Microphone for the optional intercom is seen in lower right corner Fig 1 20 The auxiliary electronics panel phones stereo can be connected one for the patient and one for the eventual assistant The microphone connector is for the intercom microphone A phantom is provided for checking the system performance see Fig 1 21 It contains 32 artificial dipoles and four head position indicator coils The phantom is based on the mathematical fact that an equilateral triangular line current produces equivalent magnetic field distribution to that of a tangential current dipole in a spherical conductor provided that the vertex of the triangle is at the origin of the sphere NM20215A G 25 4 Overview of the systen 1 11 Fig 1 21 The phantom An optional closed circuit TV monitoring system CCTV is provided for on line monitoring the patient inside the magneticall
60. ess to the skin underneath No scratching with a needle is needed Attach the cap to the subject s head and tighten the straps under the jaw so that the cap sits tightly but comfortably see Fig 1 14 Apply a liquid electrode gel such as OmniPrep Skin Preparation D O Weaver amp Co Aurora CO USA to e g a cotton swab This paste includes particles to abrade the skin Rub the skin gently ensuring that the gel wets the skin even if the hair is very thick Do not over abrade however Prepare all electrodes in the same manner After that inject hardening electrode paste e g Grass EC2 Grass Instruments Quincy MA USA with a syringe to form the actual bridging from the skin to the electrode see also Fig 3 2 Do not use a hypodermic needle on the syringe Press the electrode with your fingers against the skin while squeezing the syringe The electrode paste hardens quite rapidly A piece of paper tissue compressed on the electrode helps in drying the paste The paste can however be washed away easily with ordinary soap or mild dish care detergent such as Fairy and water Repeat this procedure for each electrode opening Refer also to the instructions given by the electrode gel manufacturers CAUTION Avoid getting the paste or gel to the eyes or mouth Use only non toxic pastes approved for clinical use After this attach the reference REF and ground GND electrodes single electrodes as explained in the next
61. essary retune the sensor For further details refer to Sensor Tuner User s Guide EEG Electrodes measurements the choice of proper electrode materials and paste gel is very important As the electrodes and the electrode cap are very close to the magnetom eter sensors they are particulary prone to cause magnetic artefacts Even a thin layer of magnetic material or a small particle of ferromagnetic dust can cause magnetic artefacts to one or more MEG channels When operated in dc coupled mode electrochemical battery potentials generated in electrodes are directly coupled into the preamplifier This causes a risk of saturating the amplifiers even in ac coupled mode since frontmost amplification stages are internally always dc coupled Further more if the connection between the electrode and skin is not stable movements tend to change the electrode potential and cause severe low frequency noise or drift NOTE The use of Ag AgCl electrodes is recommended since they are known to minimize the electrochemical battery potentials they are non magnetic see Chapter 2 4 and relatively easy to obtain It is best to have all electrodes made of same material and to use the same electrode paste gel Specifically all the electrodes of the unipolar channels and the reference channel must be of same material and use the same electrode paste gel In order to maintain good performance the AgCI coating must cover the whole electrode surface
62. etat 49 Refil SCO CUG TE RE a e a a Aaa 50 Monitoring the Helium level ueesessesssssrsesesssresrrrssrrssrrrerrsseussrrnsrrrnsennsreeetes 50 The Helium transfer procedure ss 52 Troubleshooting transfer problems cccsssscceeceeeeesneeeeeeeetsseaeeeeteeseeeees 55 Gantry bed and chair 57 CONS CMON cs aeiia e en tante tie 57 Position indicator display ss ten le nee ete 58 Changing the position of the Dewar 0 cceccscccceesssssseeeeeessesseeeeeeeessenanes 59 5 3 1 Changing the position from supine position to upright position 59 5 3 2 Changing the position from upright position to supine position 60 Positioning the patient in supine POSITION eee ee eeceeeeeeteeeeeeeeeeeeteneeette 61 Positioning the patient in Seated position cece ccessstseeseeeeeeeeeeeeeeeeeneees 61 5 5 1 Construction of the chair 61 5 5 2 Subject preparations and positioning cceeeeeeeeeesteeeeees 62 Getting the patient out in case of emergency 63 Electronics 65 Precautions sien Anne ee 65 G n raliste men into tonnes 65 6 2 1 Hack installation sinn 65 6 2 2 Electronics Control ss it ne ne 65 6 2 3 Power Supplies readers 65 6 2 4 Isolated EEG Power Supply sssssesssesenssrressenssrenreessrrssersssrnnne 65 Powerup and shutdown instructions ccccccsssssssensceceeeceeeesseceeseeseseeees 66 6 3 1 Cold start powerup after mains failure
63. euromag System Hardware Technical Manual The main system components are summarized in Figs 1 1 1 3 An example layout of the components is sketched in Fig 1 4 NM20215A G 9 El Overview of the systen Magnetically shielded room Phantom l LHe Filter Main electronics mux Probe unit gauge unit cabinet separate box unit Feed Signal and control cables through po filter Loe eT SSG p unit ee a Main MEG electronics rack Control ee E unit si MEG i teed E through pue Main EEG electronics rack Mu semer Preamplifier power supply unit MSR y i M V pe Switen through H p gt n fe bt FT aes Pa _ RT computer VME rack p x Lifting aT pe unit i i i control A See Mains distribution unit Se 2 A Figure 1 2 MEG electronics components Magnetically shielded room power unit Opto Isolated supply Control isolation Filter unit cabinet Signal and control cables Main electronics Main EEG electronics rack _ Preamplifier power supply unit Switch RT computer VME rack _ Mains distribution unit Figure 1 3 EEG electronics components 10 NM20215A G Overview of the system E PTT Vs Isolation MEG Equipment area Des Storage Analysis PC Electr iting unit liquid He cabinet Printer Eedi ps eedthroug a O
64. gCl electrodes cccessscscsceccesseceeececsssnsssnssesaeeeeeeeeseeeeeees 8 9 Annual maintenance ss rc odes haa cleus ees nn a otre an bah Appendix Basic concepts terminology ss NM20215A G List of symbols The following symbols are used in the system and in the manuals Familiarize yourself with each symbol and its meaning before operating this system Caution consult accompanying documents Parts of the system are marked with this symbol when it is necessary for the user to refer to important operating and mainte nance instructions given in the manuals accompanying the system In the manuals it also calls attention to specific instructions These instructions may contain procedures practices conditions or the like which must be correctly performed or adhered to in order to ensure safe operation and to avoid damage to the patient operator or the system Consult instructions for use Parts of the system are marked with this symbol when it is necessary for the user to refer to important operating and maintenance instructions given in the manuals accompanying the system In the manuals it also calls attention to specific instructions These instructions may contain procedures practices condi tions or the like which must be correctly performed or adhered to in order to ensure correct operation and or increased safety and to avoid damage to the system Type BF body floating equipment symbol The applied parts parts in
65. gnetically shielded room has 2 3 such con centric shells separated by a few hundred mm The room distorts the NM20215A G Appendix A external magnetic field in such a way that the magnetic field inside is substantially weaker The shielding efficacy increases with frequency Magnetometer A flux transformer coupling external magnetic signal to the SQUID detector making the SQUID to respond to the external magnetic field A magnetometer comprises a single pickup coil and a signal coil coupling the signal to the SQUID Planar gradiometer Siphon SQUID A gradiometer where the mutliple pickup coil is made of two adjacent loops The planar gradiometer is sensitive to spatial changes of the magnetic fields in a direction along the line joining the centerpoints of the lines A planar gradiometer has a focused directional sensitivity pattern and couples strongly to currents right underneath it A vacuum insulated tube for transferring liquid Helium from storage vessel to the probe unit The Elekta Neuromag transfer siphon comprises a flexible part and a fixed part Superconducting QUantum Interference Device The SQUID is an ultrasensitive magnetic flux detector based on superconductivity and so called Josephson effect It operates at cryogenic temperatures Superconductivity A state where electric resistance equals zero Present in several substanc es e g in Niobium and Lead A superconductor also repels magnetic flux i
66. here are no internal operator serviceable parts inside Head position indicator coils electrode caps headboxes and electrode interface in the side panel of the gantry are the only operator accessible parts of the EEG subsystem Use only headboxes and electrode caps supplied with the system or available as options Power supplies and grounding CAUTION The power supply of the electronics must be connected only to the power outlets inside the electronics cabinet which are connected to mains via an isolation transformer Also internal power cabling must not be changed CAUTION The 3 D digitizer power supply unit must be connected to mains via an isolation transformer supplied with the Elekta Neuromag system The main electronics is powered through medical safety isolating trans former connected to electronics cabinet outlets Therefore internal power cabling must not be changed For schematic diagrams of the powering refer to Elekta Neuromag System Hardware Technical Manual CAUTION The isolation transformers also provide step up or step down voltage conversion if needed Inside the main electronics cabinet the mains voltage is 230 V NM20215A G Safety instructions and precautions 2 A NM20215A G Main electronics cabinet Stimulus cabinet SFR C TS RF Feedthrough cabinet UZ Main grounding point To main ground at electric switchboard bu
67. icator LED goes off and re connect the powercord During startup all indicators are lit briefly in a sequence first green and then red If the problem persists or repeats often call a service representative Undervoltage detection The main elecronics power supply units have undervoltage detection circuits on the low voltage side NOTE If any output voltage of a main electronics power supply unit falls below its limit the unit will turn off all its output voltages and the indicator LED for that voltage will turn yellow If an undervoltage shutdown occurs try restarting the unit by detaching its power cord wait unit the red indicator LED goes off and re connect the power cord During startup all indicators are lit briefly in a sequence green and red If the problem persists or repeats often call a service representative or have the mains supply voltage checked by a electrician 69 6 5 70 Electronics 6 4 4 Cl A Overtemperature protection The main electronics power supply units and the Real time computer VME rack have temperature protection circuits with over temperature indicators The VME rack indicator is on the front of the rack NOTE The power supply units of the main electronics have two temperature protection mechanisms If the temperature of the power supply unit transformer exceeds the limit primary marked on the cover a thermal switch will shut off the mains supply to the unit and
68. ide of the flexible siphon when necessary for example by blowing warm gas through the siphon If you leave the transfer incomplete ensure that the transfer schedule is modified accordingly There is no flow of liquid and the pressure in the storage container does not go down even if pumping is stopped This may be caused by frozen air or moisture obstructing one or both of the siphons Stop transfer depressurize the storage container remove the flexible siphon observe the outflow of Helium and plug the fixed siphon Some Helium should emerge out of the fixed siphon head If no Helium flow appears at the end of the flexible siphon even if the storage container is slightly pressurized there is a plug in the flexible siphon If the air plug is in the flexible siphon stop transfer warm the siphon up let it dry and start again If there is no Helium flowing out from the fixed L siphon mounted to the probe unit of the Elekta Neuromag when the plug is removed the frozen air or moisture plug is within the fixed siphon Call an Elekta service representative There is excessive flow of Helium gas but no liquid is transferred and the siphon flexible or fixed feels cold The insulating vacuum of the siphon is bad and it needs to be re evacuated by service personnel Use another siphon if available Transfer does not succeed and the lower tip of the Dewar feels cold This may happen due to poor insulating vacuum The vacuum has to be
69. ilding transformer ground Figure 2 1 Grounding of the system CAUTION The RF line filters in stimulus cabinet contain large capac itors Thus voltage may remain across terminals even after the power has been switched off from the filter The filters have built in resistors which discharge the terminals in less than 10 seconds All shielding covers must be in place before applying power to the filter The filters may only be installed permanently mains plug connection of the filter is prohibited The power supply units are protected by mains primary fuses All fuses are accessible at the back plane of the MEG preamplifier power supply unit with the correct values of the fuses marked in the immediate vicinity A T before the rated current in amperes indicates slow time lag slow blow type and a F fast type If no type has been indicated use fast type fuses CAUTION To avoid risk of fire and of electric shock ALWAYS use only correct rated fuses as replacement The system except for the EEG applied parts discussed below is permanently grounded class I equipment according to IEC 60601 1 at a single point main grounding point located at the filter unit cabinet between the electronics cabinet and the magnetically shielded room see Fig 2 1 CAUTION The grounding cables must not be disconnected 33 34 Safety instructions and precautions pH 2 2 3 NOTE The system must not be grounded to any oth
70. isolation transformers if installed may only be used for the connec tion of system components or equipment needed during service and maintenance operations or for compatible user supplied auxiliary eguip ment stimulus cabinet Defibrillators NOTE The EEG subsystem is not protected against cardiac defibrillator discharge Damage to the front end may result if a defibrillator is used on a subject connected to the electroencephalograph In case of a need for defibrillation disconnect the electrodes if possible This is carried out quickly by unplugging the electrode cap or headbox connectors and the eventual single electrodes from the electrode interface panel The system cannot be used with treatment devices feeding energy to the subject such as high frequency surgical equipment 2 3 Mechanical safety A The weight of the fully loaded Dewar including liquid helium and the Dewar supporting cradle moving with the sensors is approximately 200 kg To ensure that the Dewar is prevented from falling down from the seated measurement position under any circumstances it is equipped with two completely separate and parallel support mechanisms both of which alone can withstand at least a fourfold overload compared with the normal working condition CAUTION The dewar position must not be changed while patient or patient chair is under the gantry The patient is released from the helmet in the seated measurement position by releasing the ele
71. lly hairpins the watch and jewelry worn on the head Wearing special clothing without any hooks etc may be necessary since all ferromagnetic materials cause magnetic artefacts Attach head position indicator HPT coils and eventual EOG and EEG electrodes or caps as described below CAUTION After electrodes have been attached onto the subject s head avoid contact of conducting parts of the electrodes including reference REF and isolated preamplifier signal ground GND electrodes to actual ground or other conducting parts which may be grounded or become live at mains voltage Do not ground subject to actual ground e g the wall of the magnetically shielded room Do not place conduct ing grounded objects near the subject that he she may touch while connected to the equipment NM20215A G A typical measurement with Elekta Neuromag E 3 3 1 A NM20215A G Fig 3 1 HPI coils in place Note that the subject is not yet in the actual measurement position Attaching the head position indicator coils Take a head position indicator HPI coil set with three to five coils Typically the coil sets have four coils preassembled If necessary add an additional coil by inserting the coil connector pins from the back of the HPI connector until they click in place Check that the coils are OK by connecting the coil set connector to the HPI coil tester optional accesso ry or use an ordinary ohm meter tocheck the continuity of
72. luding checking software versions Checking liquid Helium gauge Checking and changing defective and worn out parts Checking intercom and video monitor operation if installed Checking the accessories Tuning of the system Overall system performance test noise and phantom measurement calibration after the service 88 NM20215A G Appendix Basic concepts terminology A D conversion Conversion of an analog signal to digital form digitalization Anti aliasing filter A low pass filter designed to limit the signal bandwidth to less than half of the sampling frequency If the signal being digitized contains frequen cy components higher than half of the sampling frequency a phenomen om known as aliasing occurs whereby higher frequency components are folded back to lower frequencies introducing spurious signal compo nents Applied part BF type Parts of the system in direct contact with the person being investigated with the system Body floating An applied part providing enhanced protection against electrical shock An applied part of BF type must fulfill leakage current requirements specified in the standard IEC 60601 1 even in the case that the patient is unintentionally connected to an external mains voltage Cryopumping Adsorption of gases on surfaces on cryogenic temperatures See detailed description in Section 2 1 Class I device A device whose protection agains electrical shock does not rel
73. m 1 1 Intended use The Elekta Neuromag non invasively measures the magnetoencepha lographic MEG and electroencephalographic EEG signals produced by electrically active tissue of the brain These signals are recorded by a computerized data acquisition system displayed and may then be interpreted by trained physicians to help localize these active areas The locations may then be correlated with anatomical information of the brain MEG is routinely used to identify the locations of visual auditory somatosensory and motor cortices in the brain when used in conjunction with evoked response averaging devices MEG is also used to non invasively locate regions of epileptic activity within the brain The localization information provided by MEG may be used in conjunction with other diagnostic data in neurosurgical planning 1 2 General information NM20215A G Elekta Neuromag allows simultaneous measurement of 306 MEG and 64 optionally 128 EEG signals over the whole head Activity of several sources all over the cortex can thus be monitored Elekta Neuromag MEG channels are based on 306 superconducting thin film sensors inside a cryogenic Dewar vessel The gantry which supports the Dewar the patient bed and the patient chair are operated inside a magnetically shielded room MEG electronics unit outside the magnetically shielded room reads out the sensor outputs through the filter unit digitizes the signals and controls
74. m having a knot on it Lower the siphon slowly to the bottom Move the storage container into the magnetically shielded room If you have a long siphon can be ordered separately the storage container can __ Extension tube Be A Flexible siphon Filter unit Transfer exhaust hose Silicon S To storage Dewar To Hose He exhaust clam Pressurizing unit rubber balloon Figure 4 3 Parts needed in liquid Helium transfer NM20215A G 53 4 Cryogenics 54 10 11 12 13 be left outside of the room Open the right side cover of the gantry and open the precooling valve on the side panel Remove the knotted silicon hose and fasten the siphon end to the precooling socket Act rapidly to minimize the possibility of air getting into the probe unit Tighten the knurled sleeve nut slightly at the siphon If the tip of the siphon does not slide easily to the precooling holder apply a small amount of vacuum grease to the O ring If you have a long siphon with the storage container outside of the room ground the braided cover of the siphon to the magnetically shielded room wall and support the long flexible tube at least at one point the exact realization of such arrangements is site dependent Block the transfer exhaust hose with the plastic hose clamp valve Close the relief valve of the storage container Squeeze the rubber balloon gently Helium flow through the precooling hose st
75. must be left to trained service personnel 51 EI Cryogenics 4 4 52 Table 1 Liquid Helium level data Liters supine seated Liters supine seated 13 11 46 51 49 14 12 47 51 50 15 14 48 54 51 16 16 49 55 53 17 17 50 57 54 18 17 51 58 55 19 18 52 59 56 20 20 53 60 57 21 21 54 61 58 22 22 55 62 59 23 23 56 64 24 24 57 66 25 25 58 67 26 26 59 68 27 27 60 69 28 28 61 71 29 30 62 73 30 32 63 75 31 33 64 76 32 33 65 77 33 35 66 78 34 36 67 80 35 37 68 83 36 38 69 84 37 39 70 85 38 41 71 87 39 42 72 89 40 42 73 91 41 43 74 92 42 44 75 94 43 45 76 96 44 46 77 98 45 48 78 The Helium transfer procedure A Familiarize yourself with safety instructions before transferring Helium CAUTION Wear protective gloves to avoid skin contact with liquid Helium or exhaust gas or any objects that have recently been in direct contact with liquid or evaporated gas During transfer monitor pressure gauges and do not let pressure to rise above limits described below NM20215A G Cryogenics E 1 If the exhaust line is equipped with an electrical Helium gas flow meter outside of the MSR not i
76. n however easily be corrupted by careless setups of additional equipment This is especially important for MEG recordings NOTE RF intereference may deteriorate signal quality and lead to incorrect results To maintain high level of electromagnetic interference immunity all cables coming to the magnetically shielded room must be properly filtered Radiofrequency transmitters like mobile phones as well as mains operated devices and active digital electronics inside the magnet ically shielded room must be avoided altogether Use of the stimulator cabinet outside of the magnetically shielded room is highly recommend ed for other equipment There is a direct access from the stimulator cabinet to the inside of the shielded room and the stimulator cabinet is equipped with signal and mains feedthrough filters Place for example the isolation units of somatosensory stimulators inside the stimulus cabinet To avoid radiated intereference via cabling digital electronics which is active during measurement should however be avoided also inside the stimulus cabinet Electrostatic discharges The Dewar gantry and the electronics contain static electricity sensitive components To prevent flux trapping or permanent damage certain precautions are necessary Pins or connectors marked with the ESD symbol should not be touched and connections should not be made to these connectors unless ESD precautionary procedures are used G2 WO 2 7
77. nel is shown in Figs 1 12 and 1 13 On the panel there are two 37 pin male connectors 32 channels each for connecting the electrode cap or electrode headbox Channels 1 60 are unipolar single ended and accessed through the 37 pin connectors only Channels 61 64 are bipolar differential For convenience they are also connected in parallel with the second D37 connector to the eight sockets EEG61 EEG64 on the panel Separate sockets are provided for the reference REF and ground GND 19 1 Overview of the systen 20 Fig 1 12 The electrode interface panel is under the gantry side cover EEG1 EEG32 re EEG33 EEG64 A Oirean daad d pod dada 0000000000000000 0 EEG61 EEG62 EEG63 EEG64 EEG61 EEG62 EEG63 EEG64 Fig 1 13 The electrode interface panel The connectors marked EEG1 32 and EEG33 64 are used for the electrode cap and for the single electrode headbox The sockets REF and GND are for reference and ground electrodes The bipolar channels 61 64 see section 1 9 are connected to sockets EEG61 EEG64 electrodes ground and reference electrodes can also be connected via the headbox see next paragraph The electrode cap see Fig 1 14 allows a convenient way of attaching a large number of electrodes to predefined places For instructions how to use the cap see Section 3 3 Caps with different electrode configurations NM20215A G Overview of
78. ng a total of 32 trigger lines However internal trigger pulse generation is only supporting 16 lines The optional independent mode is taken into use from Data Acquisition Program For details refer to Data Acquisition User s Manual NM20215A G Auxiliary electronics Ka 7 1 2 NM20215A G 19 FRONT VIEW 1 O 0000000000000000000 O 000000000000000000 37 20 Input 1 10 Input 10 20 Output 1 29 Output 10 Input2 11 Input 11 21 Output 2 30 Output 11 input 3 42 Input 12 22 Output 3 31 Output 12 Input4 13 Input 13 23 Output 4 32 Output 13 Input 5 14 Input 14 24 Output 5 33 Output 14 Input 6 15 Input 15 25 Output 6 34 Output 15 Input7 16 Input 16 26 Output 7 35 Output 16 Input8 17 Ground 27 Output 8 36 Ground Input9 18 Ground 28 Output 9 37 Ground OQONOHALhAN gt Figure 7 1 The stimulus trigger interface unit Below pinout of the parallel multipole 37 pin connector instructions for use CAUTION If any of the equipment connected to the the stimulus trigger interface unit is patient connected all other equipment connected to the same interface unit must fulfill the safety requirements of IEC 60601 1 for medical electrical equipment Verify correct voltage and polarity and connect the power supply to the DC connector on the side of the interface box see Fig 7 1 Connect the optic link between the interface box and the main electronics cabinet The green lights Power and Link
79. ng your other hand from the down button Continue pressing the down button until the dewar has rotated to the supine position and the movement stops A green OK light on position indicator is lit to show that the system is ready for use All other indicator lights should be off Do not stop the movement unnecessarily by releasing the button Insert the bed docking piece to the base unit of the gantry Wait a few minutes for stabilization before starting measurement NM20215A G Gantry bed and chair Upper bed Wheel lock Figure 5 5 Construction of the patient bed 5 4 Positioning the patient in supine position Construction of the bed is shown in Fig 5 5 Ithas wheels and a movable upper bed both the wheels and the upper bed can be locked With the locks of the wheels open and the upper bed locked the patient bed can be moved in and out of and inside the magnetically shielded room The easiest way to move the bed is by pushing pulling it from the green handle which is located in the rear end of the upper patient bed After docking the bed into the gantry lock the wheels of the bed If the head support is used unlock the upper bed on which the patient is lying and push it towards the gantry until the patient s head is covered by the helmet Then lock the upper bed During the measurement the patient s head leans against the head support After the measurement the upper
80. nput 4 8 Input 8 17 Ground 4 21 Ground 8 Figure 7 5 Analog input connector pinout 80 NM20215A G 8 Maintenance 8 1 Maintenance program The following maintenance program is recommended Before every measurement check artefacts and noise check made by user Every morning check Helium level check MEG noise by recording signals without subject determine need for tuning tune 1f necessary made by user For EEG channels connect the signal terminators to the electrode panel and verify the operation by using the internal test oscillator test made by user After every EEG measurement cleaning of electrodes and electrode caps check for wear made by user According to a site specific user derived schedule typically about once a week liquid Helium refill made by user A fixed weekly schedule is recommended Regular phantom measurements daily or at least once a week are recommended made by user See section 7 2 Once every year annual maintenance service made by authorized service personnel 8 2 Checkup before every measurement NM20215A G Before each measurement session it is advisable to set up the measure ment fully and make at least part of the measurement first with empty room then with possible stimulators connected but with no subject and finally with the subject in the measurement position Check visually both in EEG and MEG channels for Stimulus artefacts Line interference Noi
81. ns via an isolation transformer supplied with the Elekta Neuromag system 4 on Ei A typical measurement with Elekta Neuromag 46 Fig 3 4 The head digitization goggles with additional receiver Fig 3 5 The transmitter attached to the chair Have the subject seated in the dedicated digitization chair Place the goggles firmly on the subject s head and tighten the strap see Fig 3 4 Alternatively the digitization may be performed while lying on the bed For using the bed for digitization the transmitter unit of the digitizer see Fig 3 5 must be moved from the chair to the transmitter holder table delivered with the system The transmitter is released by sliding it off from its plastic holder Under the table there is a similar plastic holder Slide the transmitter to the holder and move the table under the headrest of the bed The cable of the transmitter should point downwards chair or towards the feet of the patient bed Refer to Data acquisition User s Manual for detailed digitization instruc tions NM20215A G A typical measurement with Elekta Neuromag El BE 3 4 Recording NM20215A G If needed additional points e g electrode positions can also be digi tized NOTE Large metallic objects such as desks cabinets or the magneti cally shielded room located near the transmitter or receivers of the 3D digitizer may adversely affect the accuracy of the readings and thus
82. nstalled on all sites bypass the meter by opening the bypass valve Record the Helium level and the gas volume gauge if installed reading to the Helium transfer data sheet or log Have at least 90 liters of liquid Helium available in a nonmagnetic storage container Move the gantry to supine position Move the storage container to the magnetically shielded room entrance and connect the exhaust of the storage container to the transfer exhaust hose The hose includes a rubber balloon pump and a plastic hose clamp valve see Fig 4 2 Close the hose clamp then open the exhaust valve on the storage container and Jet the pressurizing unit balloon fill up Then close the exhaust valve open the hose clamp and squeeze the balloon Repeat this procedure 2 3 times it will flush air out of the transfer hose and balloon Close the hose clamp and the safety relief valve of the storage container Clean your hands Check that the filter unit at the tip of the thin stiff part of the transfer siphon is in place The siphon extension tube can be used if needed The extension tube is mounted between the filter unit and the vertical part of the siphon Check that the Helium exhaust line is unobstructed Lower the transfer siphon slowly into the storage container Helium gas should be let flow through the siphon in order to get air out of it Now open the hose clamp and temporarily plug the open end of the transfer siphon with a short silicon hose 12 m
83. nts typically differ slightly from the nominal value Note that the Source modelling program displays the dipole moments Q as zero to peak values whereas phantom dipole select uses peak to peak values NM20215A G 77 7 Auxiliary electronics 7 3 78 Voice intercom system option 7 3 1 General The intercom system makes it possible to communicate with the subject between and during the measurements It has been designed not to cause any interference to the Elekta Neuromag However in order to avoid disturbances the microphone should be kept further than 30 cm away from the helmet Figure 7 3 illustrates the system It is composed of a table station 1 and main station with power supply 2 The microphone 3 of the main station is inside the magnetically shielded room The microphone cable runs to the main station via the feedthrough filter The loudspeaker for main station is outside of the magnetically shielded room attached on a separate feedthrough tube on the magnetically shielded room wall 4 7 3 2 Usage To open the connection to the magnetically shielded room press CALL 11 button on the table station A short tone a green light and number 11 on the display of the table station indicate that the connection is established By default the unit operates in automatic speech direction control Note that the subject can hear what is spoken in the control room It is also possible to switch the unit to
84. on Analysis Intercom OPTION LAN Long term data storage Auditory amp electrical stimulators options a ES SRE d ih o i Filter unit Acquisition workstation Real time data acquisition system digitizer Figure 1 1 Elekta Neuromag system block diagram e Magnetically shielded room provided by third party vendor Helium exhaust system for venting the Dewar outside of the shielded room including an emergency vent line The standard EEG subsystem comprises e 64 channel electrode interface for connection of electrode caps headboxes and or four bipolar also referred as differential single electrode pairs reference electrode and ground electrode e 60 channel unipolar also referred as single ended electrode cap 32 channel unipolar electrode headbox for single electrodes e 64 channel preamplifier unit with 60 unipolar and 4 bipolar channels buffered reference channel and current limited isolated ground elec trode driver e 64 channel optoisolator filter built in the MEG feedthrough unit e 64 channel data acquisition unit e isolated power supply for the preamplifiers and for the preamplifier side of the optoisolator built in the MEG feedthrough filter unit e Control nonisolated power feedthrough filter built in the MEG feedthrough filter unit non isolated power supplied by the MEG front end power supply A range of options is also available see Elekta N
85. on the unit should be lit For using internal triggering select a stimulus channel and connect a BNC cable not supplied to the appropriate stimulator trigger output BNC connector of the stimulus I O interface unit and to the stimulator trig in connector In the data acquisition program select internal trigger ing and set the trigger channel and interstimulus interval Refer to the Data Acquisition Reference Manual If you are using several stimulators repeat the above steps as many times as necessary 73 7 Auxiliary electronics 7 2 74 Phantom Correspondingly for using external triggering select a stimulus channel and connect a BNC cable not supplied between the appropriate stimu lator trigger input BNC connector of the stimulus I O interface unit and the stimulator trig out connector In the data acquisition program select external triggering and set the trigger channel Refer to Data Acquisition User s Manual If you are using several stimulators repeat the above steps as many times as necessary In both cases the LEDs in the interface box will be lit when a trigger pulse is input or output The input channels are factory set to trigger on rising edge of TTL level pulses Select the polarity of a particular channel from the corresponding Input polarity switch located on the longer side of the unit The inputs can also be used with passive switches Therefore an internal pull up resistor is supplied Iti
86. onics cables from the top flange of the probe unit or any other internal cables Handle electronics boards only on static electricity free surfaces All strain relievers and covers must be in place before connecting power to the electronics Follow proper power up instructions see Chapter 6 3 Other precautions Never pull out or push in electronics boards with power on Switch off the power before moving or inserting any cards NM20215A G 3 A typical measurement with the system 3 1 Preliminaries If display of the MEG localization results on the anatomical MRI scans is required the MRI of the subject should be acquired and transferred into the system This can be carried out after a measurement as well MR imaging after measurment is even recommended if the patient has dental braces fills or the like that could be permanently magnetized during MR scanning To align coordinate frames nasion and preauricular points should be made clearly visible in the MRI by e g attaching on them small oil capsules visible in anatomical T1 weighted MR images 3 2 Pre experiment measures NM20215A G Open the door of the magnetically shielded room Check the inside of the room and remove unnecessary items All metallic large objects and ferromagnetic objects should be avoided altogether Keep the room and especially the chair bed and probe unit clean Adjust the gantry into either upright or supine position as described in s
87. ordinary shampoo and water NM20215A G 4 Cryogenics 4 1 Precautions A NM20215A G CAUTION As to potential hazards and necessary precautions for handling liquid and gaseous Helium refer to Section 2 1 in addition to this Section Before attempting to transfer liquid Helium read first that section and these instructions entirely When refilling the Dewar with liquid Helium one must be aware of and respect the following physical facts Liquid Helium is very cold and the latent heat of evaporation is very low Therefore Helium stays in liquid form only in specially designed vessels or transfer tubes If the liquid gets in contact with objects at temperatures higher than 4 K it will immediately evaporate and expand At room temperature the volume of the gas is 750 times larger than the liquid volume This means that a potential for dangerous pressure rise always exists if this cryogenic liquid is handled carelessly or left to warm up in a completely closed volume At liquid Helium temperature all common materials are solid This means that the vapor pressure of for example the atmospheric gases nitrogen oxygen water is practically zero in any volume containing liquid Helium which leads to cryopumping see 2 1 of these gases any Helium vessel left open to atmosphere will very effectively suck in large amounts of these gases Water freezes and may block the Helium vessel or a transfer siphon Oxygen in the probe unit Dew
88. position Contact service representative CAUTION Do not place the patient under the gantry except when the green OK light is lit NM20215A G Gantry bed and chair Lining mechanism indicator j o i Normal measurement position green Tension Dewar cradie not secured amber O timit Upper limit reached amber cat i Contact service representative red _ Elekta Neuromag 1 4 Figure 5 2 Position indicator display unit 5 3 Changing the position of the Dewar A CAUTION Do not engage the lifting mechanism if the patient is underneath the gantry The dewar can be set to two fixed positions Up for seated upright position studies with the chair and down for supine position studies with the bed The measurement array inside the helmet shaped lower part of the probe unit is tilted from vertical by 30 in the upper position and horizontal in the lower position 5 3 1 Changing the position from supine position to upright posi tion e Remove the bed and bed docking piece from the base unit and make sure that no one is underneath the dewar during position change Press the up button located in the back of the gantry see Fig 5 3 The dewar starts moving up On the position indicator display the green OK light goes off and the amber Tension indicator lights up Near the uppermost position you will hear the latches to lock Keep on pressing the up button until the dewar h
89. ressure from the probe unit of the Elekta Neuromag gauge do not let the pressure rise over 0 1 bar 10 kPa The pressure rises quickly at first When the flow of liquid starts after a few minutes the pressure goes down for a moment and then rises again to approximately 0 04 0 07 bar 4 7 kPa depending on the flow impedance of the exhaust line After the liquid starts flowing you can usually pump the balloon continuously until the transfer is complete When the desired Helium level is reached release the transfer exhaust hose clamp valve and let the pressure stabilize for a couple of minutes Detach the siphon from the probe unit when the pressure has decreased Have the plug ready Pull the tip of the siphon out and insert the plug as NM20215A G Ci pu 14 14 Cryogenics quickly as possible Tighten the plug Move the storage container out of the shielded room and lift the siphon out Use gloves to avoid frost bite Close the exhaust valve on the storage container Disconnect the transfer hose and open the relief valve on the storage container Record the time of transfer amount transferred and the reading of the gas volume gauge if installed to the Helium transfer data sheet Close the bypass valve if installed of the electrical gas flow meter Return the storage container to its place NOTE After finishing transfer check that all valves are in their normal positions that is vessels containing liquid helium
90. ror pe o BE ER Nige oe es cs Patient preparation and head digitization wt HPI chair MSR Corse equipment Video area projector Figure 1 4 A typical schematic layout of a MEG system site Note the exact composition and layout of the system is site dependent Pre X P Amplifiers flange Neck plug Cables Wiring unit Figure 1 5 Construction of the probe insert 1 4 The probe unit The Elekta Neuromag probe construction is shown schematically in Fig 1 5 The 306 sensors measure the magnetic field distribution around the head and convert itto 306 electrical signals The sensors are immersed in liquid Helium to keep their temperature stable at 4 2 K At this temperature the sensors are superconducting The 306 channel cryogenic insert contains 306 SQUID sensors positioned in a helmet shaped array NM20215A G 11 EX Overview of the systen 255 12 Figure 1 6 left Detector array side view Average distance between sensor elements 34 6 mm right Triple sensor detector unit a Figure 1 7 Main dimensions mm of the helmet shaped lower end of the Dewar The size of the helmet complies with the EN960 1994 standard and the necessary support structures and cabling The sensor insert is inside the cryogenic Dewar The 306 sensors comprise 102 magnetometers that measure the
91. rs need not be accessed directly by the user For schematic and block diagrams refer to Elekta Neuromag System Hardware Technical Manual 1 13 Computer system The standard system configuration typically includes two UNIX work stations one for performing and controlling measurements and on line processing acquisition workstation and the other for off line analysis of data analysis workstation Additional mass storage and output devices etc can be added to the system according to need For schematic and block diagrams refer to Elekta Neuromag System Hardware Technical Manual See also Fig 1 1 1 14 Cryogenic equipment A siphon is used to transfer liquid Helium from a storage container to the Dewar when a refill is needed It is a flexible vacuum insulated double wall tube The Helium gas evaporating from the Dewar is routed typically via a special exhaust system to the outside air or to a gas recovery system if available If installed the exhaust system comprises a Helium boiloff valve unit for connecting the Dewar exhaust hose and storage Dewar exhaust hose to a Helium boiloff feedthrough tube connected to a check valve This is normal ly connected via a heat exchanger to a gas meter optional The system also contains a safety vent to outside of the building comprising flexible safety exhaust duct and a Helium safety exhaust duct feedthrough A block diagram of the liquid and gaseous Helium systems is shown in
92. s causing flat or noisy channels which are not recovered by taking the subject out Detrapping using the sensor heaters is needed see Section 2 4 2 Loose EEG electrode or bad connection to skin Check connection Clean skin and re attach electrode Bad EEG cable connections Check electrode cap or headbox cable connections Reference or active ground electrodes badly connected or left open Check connection Unused EEG channel left active Unused channels should be switched off from data acquisition see Chapter 8 4 Data acquisition lock up e g red fail lights on main electronics boards stops responding connection lost reset see Chapter 6 6 8 6 Monitoring the liquid Helium level NM20215A G As part of the standard maintenance the Helium level should be checked regularly There are three differenent ways to accomplish this e Push the toggle switch of the local display inside the shielded room to turn the display on and wait for 20 30 seconds for the display to stabilize Remember to switch the display off by pushing the toggle switch again Select Helium from the Tools menu of the data acquisition program 85 8 Maintenance 8 7 86 Cleaning e Double click the icon of the Helium utility from the Maintenance folder The level is automatically recorded in computer s memory and the current level and recent history can be read from the computer screen using
93. s flattened Figure to a plane in t di b 1 8 see Fig irection ien grad NM20215A G 14 Overview of the system Planar gradiometer channel ore channel derivative along latitude mules Magnetometer channel Pa normal field component 1741 Sd nanne number Planar gradiometer channe HR ay Sensor derivative along longitude number FN Gradiometer channel Preamplifier number number Figure 1 8 b Naming convention Depending on location x 2 and 3 or vice versa refer to Fig 1 8 a Right side of the subject ae Figure 1 9 a Naming of sensor elements NM20215A G 15 Overview of the systen En a j Sa A 4 FA A i oe i 10 1 6 1 l 2 i EX vA 4 H x lt K a i i LA i a ne oe i A i Ag Aa i o i i i ann ur H Va aw Left side of the subject a Sit tener Figure 1 9 b Naming of sensor elements 16 NM20215A G Overview of the system err anil senna nen one ET Back Meeting cay Figure 1 9 c Naming of sensor elements 17 NM20215A G i a1 Overview of the systen Figure 1 10 b Upright measurement position 18 NM20215A G Overview of the system Digital flux locked loop control Buffer gt Flux transformer bi SQUID Signal Out SQUID sensor Working point control Control Signal In Figure 1 11 Block diagram of the S
94. s may happen if a powerup is made immediately following power down of the unit Power shutdown Before any electronics service operations main power must be switched off Switch off Preamplifiers Real time Computers and Main DSP elec tronics from the mains control panel Switch off the main switch on the mains control panel This will turn off the ethernet switch the roof fans and eventual equipment connected to the auxiliary sockets e g the optional intercom NOTE It may take a while before the LED indicators go off A main electronic power supply unit will not restart before all indicators are off After service operations follow the start up instructions given above 6 4 Protection 6 4 1 Fuses CAUTION To avoid risk of fire and of electric shock use only correct rated fuses as replacement 8 Eat Power Supply Unit PSU i Model EL1469N For proper rack mounting only External forced cooling in rack Output 15 5V 0BA 15 5V 1 54 i 6 3V 1 2A 6 3V 20A Fay aaa on En Z ar 15 5 0 8A 15 5V 1 5 le LED for temperature monitor SE nr ee Off normal operation Ve ovek l O Temp Red Temperature limit exceeded Power 145W Freq 50 60 Hz O 15V ue TA tae LA Indicator g Output T 70 C O ne LEDs 5 for outputs EY Ee Green normal operation Primary fuse T 4 O REN Red Current limit exceeded O 6V Yellow Undervoltage
95. s selected by sliding the corresponding Input Pull up switch to on Normally the input polarity should also be changed to falling edge if pull up is used The polarity of the output pulses can also be selected by from the corresponding Output polarity switch For specifications of the trigger input output signals see Elekta Neuro mag System Hardware Technical Manual The stimulus cabinet is available for placing various stimulator devices providing isolated power and RF filtered feedthroughs The feedthroughs are specified and explained in greater detail in Elekta Neuromag System Hardware Technical Manual Active digital circuitry e g a computer inside the stimulus cabinet should be avoided A phantom is provided for checking the system performance It contains 32 artificial dipoles and four fixed head position indicator coils The phantom is based on the mathematical fact that an equilateral triangular line current produces equivalent magnetic field distribution to that of a tangential current dipole in a spherical conductor provided that the vertex of the triangle and the origin of the conducting sphere coincide The phantom dipoles are energized using an internal signal generator which also feeds the HPI coils An external multiplexer box is used to connect the signal to the individual dipoles Only one dipole can be activated at a time The phantom is shown in Fig 7 2 and the locations of the dipoles are given
96. se Bad channels Stimuli coming if used The responses in an empty room measurement should be virtually flat lines showing only normal average noise If you encounter a problem try 81 8 Maintenance 8 3 8 4 82 CE to remove the problem by simplifying the setup as long the problem has been identified Especially try to determine which issues have changed since the system last time operated without trouble NOTE Excessive noise on the channels may deteriorate signal quality and lead to incorrect measurement Usually a few noisy channels does not however cause problems as this can be taken into account by rejection settings in data acquisition in the in source localization refer to corresponding software manuals Noise level follow up and MEG channel tuning Every day preferably in the morning the noise level of all channels should be checked by making an empty room measurement Bad chan nels if any are tuned according to Sensor Tuner User s guide Let Autotuner program run always when appropriate See Sensor Tuner User s guide It is recommended to save a good basic setup having low overall noise which is always used as the starting point for the autotuner program EEG channel checking To check the noise level of EEG channels connect the signal termination blocks 1 MQ resistance to isolated signal ground for each amplifier input to the electrode interface panel 37 pin connectors Do a mea
97. sure ment with EEG channels switched on Select the EEG channel sets in the raw data display and verify that there are no channels whose noise level clearly exceeds that of other channels or shows a completely flat line For further checking of the EEG channels use the Squiddler EEG utility program which can be invoked from the Tools menu of the Acquisition control program The control dialog is shown in Fig 8 1 The parameters are explained below Per channel parameters e Active Selected preamplifier or all preamplifiers on off Set to Off e Gain Select 5000 500 150 nominal gain actual value taken into account via the calibration coefficient Value in parenthesis indicates maximum peak to peak signal to electrode input Normally 5000 for unipolar EEG channels 500 or 150 for bipolar channels EOG EMG etc Set 5000 for channels 1 60 and 500 or 150 for EEG61 EEG64 depending on software configuration Nothing is shown in the ALL mode HPF Hardware high pass filter 3 dB corner frequency Set to 0 1 Hz NM20215A G Maintenance g Fig 8 1 Example of the Squiddler EEG utility program user interface Test Osc input Connect the internal test oscillator signal to the input of this channel Used both for bipolar and unipolar channels Test Osc must also be on see below to use the test signal Set to Off Test Osc input Connect the internal test oscillator signal to the input
98. t fatigue and head movement After the measurement lower the chair by pushing down on the release pedal backmost on the right hand side of the chair Remove table handrest lower the footrests and advise the patient minding his her head to rise from the chair or pull the the chair out and help the patient up Note Advise the subject patient to keep his her hands in the lap or on the dedicated table during the lifting or lowering to prevent limbs being left between moving parts The side plates of the chair also protect the subject s patient s arms 5 6 Getting the patient out in case of emergency NOTE In both supine and upright positions the EEG and HPI cable BH connectors ought to be disconnected prior to moving the patient if possible NM20215A G 63 Gantry bed and chair Ci NOTE In the supine measurement mode when head support is used release the lock of the upper bed and then pull the upper bed outwards In some device models it is possible using some extra force to pull the upper bed outwards from the measurement unit without releasing the locks If the head support of the upper bed is not used pull first the patient s upper body so that the patient s head is out of the helmet on the bed Release the lock if applicable In the upright measurement mode one should first lower the seat of the chair by pushing down constantly the release pedal and then by pulling the chair from underneath the helmet
99. ta acquisition software module collector versions later than 4 20 recog nizes the gain automatically Typical default settings assume default gains of 5000 for unipolar and 500 or 150 for bipolar channels depending on software configuration respectively and 0 1 Hz for high pass filter NOTE To prevent noisy signals from disturbing the analysis switch noisy MEG or EEG channels as well as unused EEG channels off from data acquisition Noisy MEG channels may interfere with other channels when on line noise reduction is used Several unused but active EEG channels may cause spurious oscillations of isolated signal ground of the preamplifier which propagate to all EEG channels The EEG pre amplifiers have built in circuitry to ground the unused channels right after the first amplification stage The acquisition control software automatically controls this circuitry When EEG is not used at all it is recommended to also connect signal terminator blocks provided with the system to the D37 connectors Remember to remove the blocks even when using only single electrodes connected to the separate sockets at the gantry panel as the sockets are connected in parallel with the second D37 connector EEG33 EEG64 pins For details of the data acquisition software see Data Acquisition User s Manual Preparation of the subject To avoid magnetic artefacts ask the subject to remove all metal objects he she is wearing Remember especia
100. tem Should the level be very low an extra refill should be performed One should not however bypass the regular filling schedule even if additional refills are performed After the Helium level has reached zero percent there is still a reserve for about 24 hours left However system performance deteriorates if the Helium level is near or below zero percent Therefore a refill should be performed before proceeding to the next measurement The system should not be left to warm up by itself if this happens re evacuation of the vacuum space of the Dewar must be performed by authorized service personnel The Helium transfer takes about one hour After the transfer it is recommended to allow the temperature in the Dewar to stabilize for about an hour before starting new measurements and check the performance of the system as described in section 8 3 Monitoring the Helium level The real time computer system takes a Helium level reading approxi mately once in an hour Readings are not taken during data acquisition The location of the He level gauge is shown in Fig 4 1 The Helium level log file can be studied with the Helium utility from the Maintenance folder or from Tools menu of the data acquisition program You can view a graphical display of the Helium level and obtain an estimate of the time when zero percent level is reached The Helium level can also be checked from the local Helium display in the magnetically shielded room
101. the MEG Maintenance folder Activate dipole 1 by entering its number to the phantom dipole control dialog and click Do it Check that the MEG signals sine wave cycles and triggers appear on the raw data display Activate Average Wait until the limit of 100 epochs is reached If you want to measure another dipole advance the dipole number in the phantom dipole control dialog and click Do it again When measuring many dipoles it is advisable to reset the MEG channels between the dipoles select Tools Reset channels Continue from step 8 When all required phantom dipoles are measured stop the measurement and save the file This file contains the responses of all measured dipoles stored as different categories Start the Source Modelling Program Open the file saved at previous step and pick up one of the dipole categories Set the sphere model origin to 0 0 0 in the head coordinate system and set the baseline from 50 to 0 ms You may want to select accurate coil definition from the DipoleFit Preferences menu Fit single dipoles to the peaks of the response For further instructions on how to fit the dipoles refer to Source Modelling Software User s Guide Compare the localization results with the positions given in Table 2 and check that the amplitudes roughly match with the dipole moment selected at step 7 due to the finite precision of the physical dipole length the measured dipole mome
102. the HPI coils The corresponding green LEDs should be lit or the coil resistance less than 10 Q If any coil is broken a new coil set must be used A HPI spare part kit for repair is also available Attach the HPI coils to the subject using skin tape such as 3M Micropore Tape 3M Corporation St Paul MN USA or equivalent or adhesive washers such as Gereonics 450097 Gereonics Inc Escon dido CA USA or equivalent One of the coils will be placed frontally up in the middle near the hair line while two others behind the ears as high as possible near the hair front on the left and right hemispheres Option ally one or two additional coils can be placed near the vertex Usually the coils should be placed high enough that they will be well inside the sensor array area CAUTION Do not use conducting EEG paste to attach HPI coils If an electrode cap is used they can be put on the cap optionally also tangling the HPI coil cables with the cap electrode wires so that the coils do not detach or move if the cable of a coil is accidentally pulled 43 A typical measurement with Elekta Neuromag 44 3 3 2 3 3 3 Paste Electrode Fabric Fig 3 2 Cross section of the electrode skin interface of the electrode cap Attaching the electrode cap The electrode cap is made of elastic fabric The Ag AgCl electrodes snap into plastic electrode holders on the cap A 6 mm opening in the plastic holder provides easy acc
103. the operation of the sensors A data acquisition system collects and routes the data to the main computer system as well as controls the electronics and data acquisition The EEG subsystem comprises an interface for electrodes a computer controlled preamplifier unit an isolation amplifier a feedthrough filter and a data acquisition unit The electrode interface and preamplifier unit are built in the MEG probe unit gantry inside a magnetically shielded room The rest of the electronics resides outside the magnetically shielded room The device is an integral permanently built in part of the Elekta Neuromag MEG system designed to be used in conjunction with MEG measurements either simultaneously or using EEG channels only It cannot be used as a stand alone unit outside of the magnetically shielded room 1 Overview of the systen A head position indicator HPI system and a three dimensional digitizer are also included in the system to determine the position of the head with respect to the sensor array The system includes a UNIX workstation for performing and controlling measurements and for on line processing of data Typically another UNIX workstation is also included for off line analysis of data The software includes programs for data acquisition and electronics control data display source modeling signal processing magnetic resonance image MRI intergration visualization of combined structural and functional data and repor
104. the separate Helium utility The boiloff rate should also be occasionally checked A substantial increase of the boiloff rate usually signifies need for service regenerating the vacuum which must be left for trained service personnel When the liquid Helium level has reached near or to 0 new liquid must be transferred A regular weekly transfer schedule is recommended NOTE Do not leave the system warm up by itself Usually however after the level has reached 0 it takes approximately one day before all the liquid is evaporated from the system Carrying out measurements during this period is possible but disturbances due to low level of Helium may occur It is good practice to ensure beforehand that replacement liquid Helium is available when needed by having a spare storage container always at hand or at least having a second independent supplier of liquid See section 4 4 for Helium transfer instructions The HPI coils and the painted parts of the Elekta Neuromag system and the HPI coils can be cleaned and disinfected with pure alcohol The upholstering of the patient s bed and chair and the wooden digitiza tion chair are cleaned with soap water or ordinary mild dish care detergent Immediately after each measurement session soak the electrode cap with electrodes in place and single electrodes in plain water for 20 minutes so that most of the paste is disolved into the water The rest of the paste is washed away with
105. ting tools 1 3 Main system components The MEG system typically comprises the following parts Probe unit with 306 channel helmet shaped de SQUID Supercon ducting Quantum Interference Device sensor array inside acryogenic Dewar Gantry patient bed and patient chair Filter unit to prevent radio frequency RF interference to the probe unit from the environment and from digital electronics Electronics for operating the sensor elements RF shielded cabinet for electronics Stimulus delivery interface for auditory stimuli Trigger line interface digital RF shielded cabinet for optional stimulators with appropriate feedthroughs for signal cables and power line Data acquisition system with real time computers Two UNIX workstations for acquisition and analysis Isolation transformers for main electronics and stimulus cabinets Head position indicator system with marker coils and drive electron ics Audio electronics with patient earphones and microphone Three dimensional digitizer non magnetic goggles and a digitizting chair Electronics to measure the liquid Helium level comprising a probe control electronics and a local display Phantom for calibration and performance verification Transfer siphon for refills of liquid Helium into the probe unit Cryogenic Accessory Kit NM20215A G Overview of the system Visual Magnetically shielded room stimulation option option CCTV opti
106. tion are possible e Internal triggering Averaging is triggered using pulses generated internally by the Elekta Neuromag data acquisition hardware these pulses are output via the stimulus I O units for triggering external stimulators e External triggering External stimulators are used in a self paced mode and the stimulus synchronization pulses are input via the stimulus I O units to data acquisition system hardware The stimulus I O system has two interface units connected to the main electronics over optical fibre links The trigger I O interface boxes are placed near the stimulators Each of the trigger I O interface boxes has 16 lines individually config urable as inputs or outputs Stimulators can be connected using individual BNC connectors or a parallel 37 pin multipole connector NOTE The BNC connectors and the parallel multipole connector are internally connected together Do not connect the parallel connector simultaneously with the BNC connectors The two interface boxes can be operated in two modes which can be set from the data acquisiton software mirror mode duplicates the signals on the first unit on the second unit which may at a physically separate place making a total of 16 trigger lines This mode which is the default may be useful in complex stimulus setups where stimulus generating equipment may be located at distinct places e optional independent mode provides parallel operation of the units maki
107. to verify that it does not cause any noticeable signals Then take the object under test in your hand and wave it under the helmet to see whether it causes any disturbances If it does it is too magnetic for MEG and should be avoided in measurements NOTE Do not bring the bar magnet inside or even close to the magnetically shielded room Do not attach the bar magnet to the magnetically shielded room wall as it will magnetize the wall material to saturation severely degrading the shielding performance NM20215A G Safety instructions and precautions ULTRASENSITIVE INSTRUMENT Magnetic objects and devices cause disturbances Inside the magnetically shielded room DO NOT e use mobile phones e bring in metal objects without permission e use electric equipment e touch the helmet unnecessarily e wear watches spectacles eye glasses during recording BH NM20215A G Figure 2 2 Recommended warning of magnetic objects Avoid bringing heavy tools into the shielded room If it is absolutely necessary keep them as far as possible from the sensors Nonmagnetic tools are commercially available Avoid using electric motors inside the room If it is absolutely necessary keep them and their power cables as far as possible from the gantry Do not use electronic flash inside the magnetically shielded room Avoid discharges of static electricity on any part of the probe unit The humidity in the magnetically shielde
108. uch as Gereonics 450097 Gereonics Inc Escondido CA USA or skin tape such as 3M Micropore Tape 3M Corporation St Paul MN USA can also be used if applicable After use the electrodes can be cleaned following the instructions given by the electrode manufacturer CAUTION Avoid getting the paste or gel to the eyes or mouth Use only non toxic pastes approved for clinical use Before entering the magnetically shielded room it is recommended to check the electrode impedances using an ac coupled meter such as Grass F EZMS Grass Instruments Quincy MA USA if available The preamplifier is stable for electrode impedances up to 50 kQ However to minimize low frequency noise and line interference electrode imped ances should be below 20 kQ For optimum performance impedances below 10 kQ are recommended The single unipolar reference and ground electrodes can be plugged in the headbox during the preparation Bipolar electrodes such as for EOG and EMG are connected to the electrode interface panel on the side panel of the gantry inside the magnetically sielded room Digitization of head position indicator coils Determination of the position of the head position indicator coils and optional head shape digitization is performed with the help of Polhemus 3 D digitizer included in the system Digitization is performed outside of the magnetically shielded room CAUTION The 3 D digitizer power supply unit must be connected to mai
109. und electrode within acceptable limits In addition the ground driver can also be actively controlled so that the ac signal components above approximately 5 Hz seen on the reference electrode input are compensated for by the active ground driver Consequently the potential difference between the patient and isolated preamplifier signal ground is smaller than without the active grounding circuit and results in a better common mode interference rejec tion Another way to understand the operation of the circuit is that active ground reduces the impedance of the ground electrode by a factor of 10 The ac signal from the reference electrode to the active ground driver can be switched on and off by using the Squiddler EEG utility program When in off position the input of the ground driver is connected to isolated preamplifier signal ground The active ground driver socket on the gantry side panel and headbox is labelled GND as is customary in the EEG practice although the term strictly speaking refers to isolated preamplifier signal ground potential Ground electrode should always be connected to the terminal labelled GND on the side panel or headbox when making measurements EEG isolated preamplifier signal ground GNDi Ground potential signal zero level of the EEG preamplifier system As patient safety regulations require this ground is isolated from all other grounds in the system including the shielded room Thus the
110. unit and push against the helmet The front coil should point somewhat upwards Connect the 32 pair cable between the phantom excitation multiplexer and the phan NM20215A G 75 Table 2 Phantom data Fixed head position indicator coils x mm y mm z mm Dist from center mm 79 5 0 0 0 0 79 5 0 0 79 5 0 0 79 5 79 5 0 0 0 0 79 5 0 0 79 5 0 0 79 5 Dipoles length 5 0 mm Dipole x mm y mm z mm Dist from center mm 59 7 0 0 22 9 64 0 48 6 0 0 23 5 54 0 35 8 0 0 25 5 44 0 24 8 0 0 23 1 34 0 37 2 0 0 52 0 64 0 27 5 0 0 46 4 54 0 15 8 0 0 41 0 44 0 7 9 0 0 33 0 34 0 0 0 59 7 22 9 64 0 0 0 48 6 23 5 54 0 0 0 35 8 25 5 44 0 0 0 24 8 23 1 34 0 0 0 37 2 52 0 64 0 0 0 27 5 46 4 54 0 0 0 15 8 41 0 44 0 0 0 7 9 33 0 34 0 46 1 0 0 44 4 64 0 41 9 0 0 34 0 54 0 38 3 0 0 21 6 44 0 31 5 0 0 12 7 34 0 13 9 0 0 62 4 64 0 16 2 0 0 51 5 54 0 20 0 0 0 39 1 44 0 19 3 0 0 27 9 34 0 0 0 44 4 64 0 0 0 34 0 54 0 0 0 21 6 44 0 0 0 12 7 34 0 0 0 62 4 64 0 0 0 51 5 54 0 0 0 39 1 44 0 0 0 27 9 34 0 NM20215A G 10 11 12 13 tom Connect the separate HPI coil set connector of the phantom to the connector of the HPI cable connected to the HPI outlet underneath the side cover of the gantry Start the measurement Do the head position measurement in the usual way as decribed in the Data acquisition User s Manual Start the phantom dipole control utility program by double clicking its icon in
111. vation mechanism of the chair and pulling the chair from underneath the Dewar For instructions see chapter 5 5 Additionally it is possible in the supine measurement position to get out from the helmet by pulling strongly the upper patient bed even if it is locked see Chapter 5 4 Have the unit regularly serviced according to the maintenance program see chapter 8 1 This must be accomplished by trained service personnel only 2 4 Trapped flux in the sensors NM20215A G Strong magnetic fields in the vicinity of the sensors may cause magnetic flux to be trapped in the superconducting thin films due to their limited 35 2 Safety instructions and precautions 36 2 4 1 capability of repelling magnetic flux completely In particular if magne tized objects like magnetic electrodes or hairpins are brought inside the helmet against the surface flux trapping may occur Trapped magnetic flux in the dc SQUID manifests itself as a greatly reduced modulation depth of the flux vs current characteristics The point of operation also changes As a result the SQUID feedback loop may not lock any more after flux trapping or the noise level may be increased resulting in deteroriated signal quality Flux trapped in the flux transformer structures may manifest itself as discrete jumps in the output level causing rejections of evoked data Normal performance can however be recovered by detrapping see 2 4 2 In the detrepping proce
112. worn or scratched coating may result in electrochemical battery potentials saturating the amplifier NOTE Gold coated electrodes are not recommended since most often they contain a magnetic intermetal layer making them incompatible with MEG measurements Also some commercially available Ag AgCl elec trodes contain nickel or other magnetic material all electrodes must therefore be tested before using them with MEG see Chapter 2 4 1 The electrode caps supplied with the system are made of sintered Ag AgCI and tested to be non magnetic Note that electrode caps available commercially elsewhere may be incompatible with MEG NM20215A G Safety instructions and precautions For cleaning disinfecting and maintenance of the electrodes refer to Section 8 7 2 6 Electromagnetic compatibility CH Ci 2 6 1 NM20215A G NOTE Medical electrical equipment needs special precautions regard ing electromagnetic compatibility EMC It needs to be installed and put into service according to the EMC information provided in this manual and Elekta Neuromag System Hardware Technical Manual NOTE Portable and mobile RF communications equipment can affect medical electrical equipment Electromagnetic interference The probe unit including the EEG preamplifiers and the electrode interface is placed inside a magnetically shielded room and all cables to the inside of the room have been carefully filtered This immunity ca
113. y only on basic insulation but also has a permanently connected protective earth connection so that accessible metal parts cannot become live if basic insulation is damaged D A conversion NM20215A G Conversion of a digital signal into analog form 89 A Appendix 90 A thermally insulated vessel for cryogenic liquids It has a vacuum insulated double wall structure The vacuum space also houses thermal radiation shields Feedback loop Flux locked loop A readout method for the SQUID sensor where the output of the preamplifier is fed magnetically back to the sensor In this configuration the sensor acts as a null detector while the feedback effectively compen sates for the input magnetic field The feedback signal is thus equal to the input magnetic field a copy of the feedback signal is then used as the output Flux locked loop provides a linear input output relation whose calibration is to a large amount independent of individual component gain variations Flux transformer A superconducting circuit comprising at least two coils connected in series Because of superconductivity magnetic flux is conserved Thus a magnetic field imposed on one of the coils will induce a shielding current to flow in the circuit cancelling the effect of externally imposed flux Since the shielding current will induce a magnetic field in other coils belonging to the circuit a flux transformer can be used to scale magnetic field intensity b
114. y shielded room during the measurement A two way voice intercommunicator option is used for communicating with the patient inside the magnetically shielded room during the measurement Interface to stimulus electronics A 16 channel trigger pulse digital input output interface is provided for synchronizing the measurement software and stimulators not supplied with the standard system used for evoked response studies The inter face unit is optically isolated from the main electronics and data acqui sition system The RF shielded stimulus electronics cabinet is used to prevent possible RF disturbances caused by stimulus devices from entering the magneti cally shielded room RF filtered feedthroughs are available between the inside and the outside of the cabinet Active digital circuitry e g a computer inside the stimulus cabinet should be avoided 1 12 Data acquisition system 26 The data acquisition system includes interface units to import and export digital signals It imports the 306 MEG channels and the 64 EEG channels In addition it handles the control of the MEG and EEG electronics as well as the timing parameters of the system The system also takes care of the trigger signals The data acquisition system consists of parallel real time computers that are connected to a single acquisition workstation via an Ethernet Switch NM20215A G Overview of the system 1 Normally the operations of the real time compute
115. y varying the coil parameters EEG active ground See EEG Ground terminal EEG bipolar channels Differential channels Channels with terminals for both the positive and negative amplifier inputs separately for each channel The reference is irrelevant for differential channels EEG channels 61 64 are differential in the standard configuration EEG ground terminal Active ground A terminal for attaching an electrode to equalize the potential of the subject with respect to the preamplifier signal ground As described above the pre amp unit is floating Thus there has to be a way to set it to acommon potential with the subject in order to keep the input amplifier at linear operating range over extended periods of time and to minimize the common mode voltage between the subject and the amplifier Traditionally this has been accomplished by connecting the isolated preamplifier signal ground directly to the subject with an EEG electrode However there are drawbacks with this approach in a fault condition the NM20215A G Appendix A maximum patient leak current allowed by patient safety regulations may be exceeded and the amount of common mode interference is affected by changes in the impedance of the reference electrode To work around this the subject is connected to isolated preamplifier signal signal ground by means of a current limited amplifier driver that even in a fault condition keeps the current of the gro

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Elekta Neuromag® System Hardware