Dose Monitoring - The Captured Image
Contents
1. ALL button to remove all examination cases and associated statistics or the CANCEL button if you do not want to remove the examination cases after all _ __ a 2208 199801 2 3 ADC Compact Dose Monitoring Software SAVE The reference dose levels of the statistical listing can at any time be saved on a floppy disk In order to do so proceed as follows 1 Insert a floppy disk into the appropriate drive 2 Click SAVE in the Dose Monitoring screen The system returns the following screen AT Dose Monitoring Enter the filename 4 Click OK 24 2208A 199801 m ADC Compact Dose Monitoring Software Useful Guidelines Defining optimal doses If the digital radiology technique is new to a department then over the first months after an ADC Compact system has been installed various examination cases may be tried having slightly different dose settings to determine the optimum dose for each case Of course while the staff is becoming familiar with the new technology no Dose Monitoring Software reference levels should be calibrated Therefore you should wait until all operators can fully master the system before performing any calibrating operations Meanwhile you should monitor the current examination statistics on screen occasionally and look at the figures to determine which examination cases have settled at nearly constant dose levels T2. This value changes continuously as the history record itself is updated with each image scanned This value will be used as reference level when the associated examination case switches from PENDING to AUTO or after an UPDATE or UPDATE ALL command if the record is already complete i e when complete 100 Sdev history the standard deviation of the collection of dose samples within the history record This measure gives an indication of the fluctuations among the last 50 exposures of this examination case A small value e g less than 0 2 indicates that dose for the present examination case was well under control in the recent past Sdev reference a snapshot of the standard deviation of the set of dose samples taken This parameter gives an indication of how well dose was under control at the moment of determining the reference level of the present examination case If it is larger than 0 2 it may be advisable to update the reference level based on the current statistics at least if the current standard deviation is much smaller 208A 199801 1 5 ADC Compact Dose Monitoring Software Reference this is the reference dose level used by the Dose Monitoring Software to determine the dose deviation for each incoming dose of the present examination case It is set to the value History when the associated examination case becomes ACTIVE or it is updated to the latter valu
3. are common and should be acceptable in most cases Deviations larger than or 0 3 log units factor of 2 if these occur frequently then you should verify the stability of the X ray equipment using the appropriate calibration instruments 2208 199801 7 ADC Compact Dose Monitoring Software Systematic deviations occurring only with a few examination cases you should determine whether the actual exposure conditions for the given examination case have not been modified kV and mAs usage of filters or grid If this is the case and the modification was intentional because of some new exposure guidelines then the corresponding reference level has to be erased in the Dose Monitoring Software database and the new reference level has to be determined by restarting the self calibration programme for the current examination case This procedure is described in the section Determining the reference levels and must be carried out under responsibility of the key operator If the X ray equipment is well calibrated and you have verified that neither the exposure conditions nor the ADC Compact ID Software parameters have been modified then you should verify the Digitizer sensitivity using the optional ADC Compact Test Phantom Set and ADC Compact Auto QC Software or you must call the service technician if the dose deviations continue to exceed the limits of 0 3 log units Bar indicator does not appear anymore If this happen
4. 08 199801 The operation of the ADC Compact Dose Monitoring Software comprises two parts determining the reference dose levels for different examination cases normal usage by all operators The first part is critical to the proper functioning of the Dose Monitoring Software and must be carried out under strict control of the key operator This topic is explained in the chapter Determining the reference levels Normal usage is straightforward and will be explained in the next sections Dose deviation indicator The most relevant control parameter is the deviation of a dose with respect to a reference level which is a direct indication of under or overexposure for the current examination case The amount of deviation is displayed on the processing and preview monitors if any and printed as a bar indicator in the film footer If the dose level is higher than the reference the black horizontal bar will extend to the right from the middle of the scale anda lower level causes the bar to extend from the middle to the left If the deviation is less than 1 exposure point then the bar is truncated to zero length making it invisible This is an indication that the dose was very close to the reference level Tick marks are positioned at 0 3 log dose intervals corresponding to subsequent dose doublings The full scale values are equal to 0 7 log units which correspond to under or overexposure respectively by a factor of fi
5. ADC COMPACT DOSE MONITORING SOFTWARE USER MANUAL TABLE OF CONTENTS ADC Compact Dose Monitoring Software Why Dose Monitoring What is Dose Monitoring What is measured How to use the Dose Monitoring Software Dose deviation indicator Abnormal indications The actual dose level IgM Determining the reference levels How self calibration works Using the Dose Monitoring Software Special functions Useful Guidelines Defining optimal doses Activating the Dose Monitoring Using the system Fine tuning the Statistics List Performance requirements 17 25 25 25 26 26 27 2208A GB 199801 i 2208A 199801 ADC Compact Dose Monitoring Software Why Dose Monitoring In computed radiography the image density is automatically adjusted by the image processing independently of the applied dose In fact this is one of the key advantages of the new technology It helps to reduce the retake rate significantly but at the same time this feature may hide occasional or systematic under or overexposure While in conventional radiography the amount of exposure is directly related to average density in computed radiography it determines the signal to noise ratio not the image density The higher the dose the better the SNR This is good news as such but in the long term there is a risk of gradually drifting to higher doses as the more exposed images tend to look better For that reason Agfa has developed a quality con
6. Compact Dose Monitoring Software During normal operation the system automatically records the dose level for each exam type encountered These records are used as a basis for determining the reference levels This means that the Dose Monitoring Software does not explictly impose any dose settings to the user On the contrary it adapts itself to the actual dose levels that are being applied in the hospital over a calibration period Once calibrated the Dose Monitoring Software stores the reference levels and for each subsequent exposure it informs the operator in case of significant deviation from reference As a result dose monitoring will stimulate applying constant doses and at the same time provide the flexibility to cope with distinct dose requirements for specific examination cases and even with varying preferences of different departments and hospitals ADC Compact Dose Monitoring Software What is measured In the ADC Compact Digitizer the photomultiplier gain is adjusted to the expected range of dose for each examination case The gain is specified by the readout exposure class which is set for each examination to the appropriate value using the ADC Compact ID software The large dynamic range of 500 1 provides for ample margin both for under or overexposure Shifts of the actual dose range are automatically compensated by image processing as long as the operating range of the detector is not exceeded Thus constant density is g
7. atient dose that must be applied in order to get a constant dose on the imaging plate varies as a function of e g patient weight and kV It should also be noted that the computed dose level is not an absolute quantity in terms of mR but is relative to the position of the detector operating range which is adjusted in terms of exposure class setting on the ID Station However once the exposure class is selected the IgM value is directly related to X ray dose in the sense that e g doubling the dose will cause the IgM value to increase with 0 3 log 2 On the other hand for a fixed X ray exposure the IgM value will vary with the specified exposure class setting of the ADC Compact Digitizer If the exposure class is doubled without altering the mAs setting then the IgM value will decrease by 0 3 log And finally it is clear that the ADC Compact Dose Monitoring Software is not a substitute for an X ray dose meter The scope of the ADC Compact Dose Monitoring Software is to provide direct dose feedback for each individual image based on the actual pixel data and to improve consistency in the long term across examinations with different dose requirements The second goal is achieved by displaying the deviation of each individual dose from a reference which may be set to a different level for each examination case es 2208 199801 5 ADC Compact Dose Monitoring Software How to use the ADC Compact Dose Monitoring Software 22
8. based on in house experience with the system Multiple IgM values are printed if the image is partitioned each referring to a single image frame 2208 199801 ADC Compact Dose Monitoring Software Determining the reference levels 2208A GB 199801 Generally the reference dose level differs for individual examination cases and varies among hospitals Therefore the Dose Monitoring Software is provided with a self calibration mechanism which will automatically determine the reference dose level for each examination case that is routinely performed in the hospital The reference levels are computed on a statistical basis by observation of dose levels during a calibration period This period is not strictly limited in time and will generally vary for different examination cases The more frequent the examination case the sooner the calibration period for that case will terminate since calibration requires fifty exposures of each examination case Calibration runs automatically while the system is in normal use but the operator should be aware that in this period the system is learning its reference levels from the individual exposures so specially during this period he she should be encouraged to apply the correct dose to each examination case consistently Once they have been calibrated the reference levels remain fixed unless the key operator undertakes specific actions as will be described later How self calibratio
9. e at each subsequent UPDATE or UPDATE ALL command If there are no further operator commands it remains fixed 1 6 2208A 199801 m ADC Compact Dose Monitoring Software Special Functions This section gives a detailed description of the various functions that are available You should read this section carefully before using any of the critical functions like UPDATE ALL and especially REMOVE and REMOVE ALL which will irreversibly erase calibration data FIX The FIX function sets the reference dose level of a specified case to a specified value In order to do so proceed as follows 1 Select the case you want to assign a specific reference value to foe Dose Monitoring 200 199801 ADC Compact Dose Monitoring Software 2 the FIX button in the main Dose Monitoring screen The system returns the following window Type the IgM value you want to assign to the selected case then click the FIX button Pm Level 1 8 2208A 199801 ADC Compact Dose Monitoring Software In the statistics listing of the main dose monitoring screen the status of cases thus fixed are marked with the label F ixed The dose reference value assigned to a specific case remains unchanged until the next FIX UPDATE or REMOVE command Dose Monitoring UPDATE The UPDATE function
10. g image is analyzed for its examination signature If the latter is recognized in the database then the current dose level is stored at the appropriate entry associated with the examination case at hand This way dose statistics are collected on the fly for all common examination cases In each database entry space is provided to store the dose levels of the fifty most recently acquired image frames corresponding to the same examination case Statistics of a specific case are called complete if at least fifty values have been collected When the statistics of an examination case are complete the arrival of an extra incoming image frame of the same examination case will cause the oldest dose value to be deleted from the collection This way the Dose Monitoring programme establishes in its database a set of history records of the most recent dose levels for all commonly applied examination cases es 2208 199801 1 1 ADC Compact Dose Monitoring Software The reference levels are computed per examination case from its collected statistics As soon as a set of statistics is completed the reference level is taken as the median out of the record of the most recent exposures This concludes the calibration period for the examination case However the updating of the history records continues after the reference level has been fixed As a result new reference levels can be specified at any time according to the values of the most recent statis
11. his is the case if is smaller than 0 2 and if the corresponding history record is sufficiently large i e complete is at least 30 As a result you can see the evolution of the frequency and consistency of the examinations performed Activating the Dose Monitoring After this period of learning and fine tuning you can now update all the examination cases You do this by selecting the UPDATE ALL button in the Dose Monitoring main screen See the section Update for more detailed information on this command Now the most frequently practised examination cases will have completed their history record i e complete 100 which means that they have collected at least 50 exposures of the same examination case in the past When you click the UPDATE ALL button the reference levels of the complete examination cases are set to the value labelled History This is the median of the fifty most recent dose levels of the same examination case that have been collected in the Dose Monitoring Software database It is considered to be the most representative for the current examination case according to recent practice within the department 2208 199801 25 ADC Compact Dose Monitoring Software Therefore when you select the UPDATE ALL button these values are frozen They are used as reference levels in the future Examination cases that are not yet complete i e for which complete is s
12. maller than 100 will set their corresponding reference level exactly the same way as soon as they are complete after having collected sufficient additional dose samples Using the system As a consequence of completed statistics over the next few months the dose deviation bar indicator will appear for many other examination cases If certain examination cases deviate systematically from the reference the applied doses may have moved to a different level If the shift to a different level is intentional you should recalibrate the system for the current examination case Using the Dose Monitoring main screen determine whether the average dose has actually moved to a different level You can do this by viewing the difference between the current reference level Reference which has been fixed since the last UPDATE and the History value which reflects the actual levels applied recently You should use the index value Case to apply an UPDATE for this individual case Fine tuning the Statistics List After a purging operation the freed database entries are occupied by the first examination types encountered that are not yet registered so make sure that the more interesting cases get their turn shortly after purging otherwise the database could be filled up again with less relevant cases 26 2208A 199801 m ADC Compact Dose Monitoring Software Performance Requirements Processing server ADC Compact Autoproces
13. n works The first time the Dose Monitoring Software is used it does not know any kind of examination case It will learn distinct examination cases as the ADC Compact extracts the exam info from subsequent readings Each time an examination case is encountered which is not yet in the database a new entry is created for it The database can store up to two hundred entries This should be enough to handle all cases frequently applied This limit has been set because it rarely happens that there are more than two hundred examination cases Thus a lot of time would be needed to collect sufficient statistics to determine the corresponding reference level ADC Compact Dose Monitoring Software In the Dose Monitoring programme each incoming image is assigned to some examination case on the basis of the next six parameters main exam sub exam radiologist exposure class scan resolution type plate type Thus an examination case is fully identified by a specific combination of these parameters also called the examination signature Each case differing by at least one parameter from the other cases already present in the database is recognized as new case and a new entry is allocated to it This will happen as long as there are free entries in the database up to two hundred This way the programme automatically learns about the most frequently used examination cases in each individual system During normal operation each incomin
14. r Dose 22084 199801 1 3 ADC Compact Dose Monitoring Software 2 Clicking this button opens a window displaying the Dose Monitoring screen 2208A GB 199801 Dose Monitoring Each entry on the screen is listed together with Created the date when the entry was created in the database i e when the first exposure of the given examination case was encountered after installation of the Dose Monitoring Software or since the last UPDATE or UPDATE ALL commands complete the completeness of the history records A record is 100 complete if at least 50 dose samples of the associated examination case have been collected ADC Compact Dose Monitoring Software Status PENDING P the history records are not yet complete but Dose Monitoring is ACTIVE MPA CHEST KISS xo 0 d t 0 0 4 GPA OLIMAR T 00 AUTO A lt date gt dose monitoring is fully operational AUTO for the given examination case since lt date gt gt ACPA a 10 0 zi ow 2 20 FIX F cases have the status FIX when their reference dose level is set to a specified value Main Examination Sub Examination Class Scan Resolution Plate Type these parameters fully specify the current examination case History the median value of the most recent history record
15. re sets the reference dose level of a specified case in accordance with or on the basis of the actual statistics last fifty exposures In order to set the reference dose level of an examination case to the last currently valid statistics proceed as follows _ lt _ 2208 199801 ADC Compact Dose Monitoring Software 1 2 Note 2208A GB 199801 Select the case of which you want to set the reference dose level to the actual statistics The system returns the following window a n N Click the UPDATE button in the main Dose Monitoring screen In case the UPDATE command is given repeatedly the reference values are each time updated on the basis of the currently valid statistics without affecting however the statistics proper UPDATE ALL Using UPDATE ALL all existing cases and those created at a later stage are automatically assigned a reference value according to the currently valid statistical data in the same way as with the UPDATE command The UPDATE ALL command overrides the reference level of all cases except those that have been set using the FIX command ADC Compact Dose Monitoring Software In order to update all cases proceed as follows 1 Click the UPDATE button in the main Dose Monitoring screen The system returns the following screen i a 2 Click the ALL button to update all examination cases or the CANCEL button if you do not want to update
16. s at a certain moment with any examination case that did show the indicator previously this might be attributed to the fact that one or more of the following items have been modified using the ADC Compact ID Software radiologist name exposure class scan resolution type or imaging plate type If so the system will normally recognize this as a new examination case and will create a new entry for it in the Dose Monitoring Software database at least if there is still space left After fifty exposures of this new examination case the bar indicator will automatically reappear It is good practice however to explicitly control the self calibration procedure after modifications have been made to the ID menus to ensure consistent setting of the reference levels This procedure is described in the chapter Determining the reference levels and must be carried out under responsibility of the key operator 2208A 199801 ee ADC Compact Dose Monitoring Software The actual dose level IgM Next to the deviation bar indicator the actual dose level is printed in the film footer as the numeric quantity IgM This figure indicates whether the dose is appropriate for the given exposure class setting It may be used for less frequently practised examination cases for which the system does not have a reference level in its database In these cases the department can use a single fixed reference level or a small table of references for special cases
17. sing Software 2208 199801 27 ADC Compact Dose Monitoring Software Printed in Belgium Published by Agfa Gevaert N V B 2640 Mortsel Belgium AG FA 2208A GB 199801
18. stogram The position of the main histogram lobe along the horizontal axis indicates the dose level relative to the detector operating range Generally the main histogram lobe must be near the central part of the detector range in order to keep sufficient margin for under or overexposure For each image read the histogram is computed and the dose level is determined as the median of the logarithmic pixel values in the main histogram lobe This value is labeled IgM The median value is obtained by sorting all contributing pixel values in ascending order and taking the middle of the series As regards the histogram the median subdivides the main lobe into two parts of equal area under the histogram curve meaning that in the main lobe there are as many pixels with lower value than the median as there are pixels with higher values ADC Compact Dose Monitoring Software If the images are collimated the histogram is constrained to the pixels within the diagnostic image part which excludes the collimation borders These regions are automatically recognized by a separate expert programme The latter programme will also partition the image into distinct frames in case of side by side exposures on the same imaging plate In this case the dose level IgM will be determined for each image frame separately It is important to note that the dose level IgM does not refer to patient dose but is a measure of dose captured by the imaging plate The p
19. the examination cases after all REMOVE The REMOVE command clears the examination case its reference dose level and the associated statistics for a specified case As a result the dose monitoring is discontinued and the dose bar indicator disappears for the specified case After the REMOVE command new statistical data is gathered starting from scratch 220 199801 2 ADC Compact Dose Monitoring Software 2 2208A GB 199801 In order to remove the reference dose level and the associated statistics for a specified case proceed as follows Select the case of which you want to clear the reference dose level and associated statistics The system returns the following window a Click the REMOVE button in the main Dose Monitoring screen REMOVE ALL The REMOVE ALL command clears the reference dose level and the associated statistics for all cases except those that have been set using the FIX command As a result the dose monitoring is discontinued and the dose bar indicator disappears for the specified category After the REMOVE ALL command new statistical data is gathered starting from scratch ADC Compact Dose Monitoring Software In order to remove the reference dose level and the associated statistics for all cases proceed as follows 1 Click the REMOVE button the main Dose Monitoring screen The system returns the following screen 2 a 2 Click the
20. tics Once they have been determined the reference levels remain fixed until explicit actions are taken The dose deviation indicator only appears when the reference level for the associated examination case has been determined i e after at least fifty exposures of the same examination case have been read 1 2 2208A 199801 ADC Compact Dose Monitoring Software Using the Dose Monitoring Software During its life cycle a registered examination case will be in one of three states When an examination case is encountered for the first time it is automatically entered into the database and it is assigned the initial state PENDING At this stage the dose deviation indicator is not yet displayed or printed as the statistical data is still incomplete and therefore unreliable The examination case will move to the state AUTO when the associated statistics become complete i e after fifty exposures The dose deviation indicator is displayed for examination cases in this state At any time an examination case can be assigned a specific value other than the reference value using the FIX command giving the case the state FIX In order to access the Dose Monitoring screen proceed as follows 1 the general System Monitoring screen of the ADC Compact Autoprocessing application or Interactive Processing application if installed click the button labelled Dose the upper right corner of the main toolba
21. trol tool called ADC Compact Dose Monitoring Software 2208 199801 1 ADC Compact Dose Monitoring Software What is Dose Monitoring 2208A GB 199801 The ADC Compact Dose Monitoring Software is an optional software package that supplies numerical and visual feedback on the actual median dose captured in the imaging plate with respect to an exam specific reference level Once the software package has been properly installed and calibrated it determines the median absorbed dose in each digitized image and compares this figure with a stored reference dose The current deviation from the reference dose is shown in the footer of images displayed on the image processing or preview monitors in case the ADC Compact Preview Software has been installed and is also printed as a bar indicator at the bottom of the hardcopy image For each distinct examination case the dose may differ therefore an entire table of reference levels is maintained internally one for each case The dose setting policy for which the radiologist is responsible generally differs from hospital to hospital Therefore the reference levels are not fixed in advance by the manufacturer These must be established in the hospital where the system is in use according to prevailing practice Reference levels for the most frequently applied examination cases are automatically determined by means of a self calibration programme which is incorporated in the ADC
22. uaranteed despite dose fluctuations Although image density shift as the direct consequence of inappropriate dose control is eliminated by image processing the main reason for carefully applying the correct dose remains i e achieving constant image quality and avoiding unnecessary patient dose If the image is underexposed it will be too noisy Overexposure yields good images but may cause unnecessary patient dose In extreme cases the Digitizer may exceed its operating range causing some parts of the image to be uniformly black with potential loss of information 2208 199801 3 ADC Compact Dose Monitoring Software 2208A GB 199801 The histogram in the figure below shows the relative occurrence of all pixel values in the unprocessed image The horizontal axis represents pixel values on a logarithmic scale The broader lobe of the histogram roughly corresponds to the pixels within the region of interest The side lobe at the left is attributed to pixels belonging to the collimation borders In these areas only scattered radiation contributes to the image The narrow peak corresponds to the background area where X rays reach the image detector without attenuation histogram frequency MAIN HISTOGRAM LOBE reference gt level relative exp IgM 3 3 log 4 REN exposure deviation DETECTOR OPERATING RANGE The median dose and the corresponding dose deviation are determined from the image hi
23. ve ADC Compact Dose Monitoring Software Dose deviation indication using the ADC Compact Preview Software In case the Dose Monitoring feature has been toggled to ON in the Configuration menu of the ADC Compact Preview Software the images displayed on the preview monitor also feature in their footer the dose deviation bar indicating possible under respectively over exposure for the current examination case Dose deviation indication using the ADC Compact Interactive Processing Software on the PS 5000 The dose deviation bar is situated under window and level in the open mode Exposure info in the info button gives exposure level IgM exposure deviation is the deviation from the reference value for this examination case Dose Monitoring Birth date PA 28 01 97 Skull PA Patients ID Comments 13 46 07 Department B RIS ID HOSPITAL DEPARTMENT 10042CC 11MC 300EC 000LR 000NR 000L M 210 W L 173 232 N lt 5200AA2980 2 Skull PA Dose deviation bar indicator in text box on film Notice that the bar indicator is not displayed if the self calibration programme of the current examination case is not yet complete which will take at least fifty exposures of the same examination Abnormal indications It is the responsibility of the radiologist to determine the allowable tolerances of dose and whether a retake is proper in case of severe underexposure As a rule of thumb however deviations up to or 0 2 log units
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