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ULTRASIM User`s Manual ver 2.1, Program for Simulation of

1. 46 6 2 4 Contourplots 47 6 2 5 Color encoded 47 6 3 Volumetric Visualization 47 6 3 1 Observation 47 6 3 2 Slice Plot 49 64 Coarray Tools 51 7 PLOTTOOL 53 71 Fie 53 722 Axis 54 73 Options 55 74 Tezt 59 8 REFERENCES 57 A INSTALLATION 59 A l System Installation of ULTRASIM 59 A 2 User Installation UNIK 61 A 3 PC Installation 61 April 8 1998 4 ver 2 1 ULTRASIM USER S MANUAL A 4 Setup for Developing your own Functions 61 B PROGRAMMING 63 B 1 Advice for ULTRASIM programming 63 B 2 Responsibilities for files 64 C ULTRASIM VARIABLES 65 CT Introduction 65 C2 Mare ON ed PL De o ske ra A 65 GE EEE EEE GE OE AT An ee 66 22 NE DEE A EE SEE EEE a 66 GI Een SAUCE ug esse TE ee 67 EL Transducer Aas pt EN 67 C 3 2 Rectangular and Curved Arrays 67 CI li II 68 Cal Exita liO es peer GL a ASS SS UE a 69 C 4 1 Excitation transmitted signal 69 C 42 Excitation beamforming 70 x ICO See DE GS WA aa 70 Gdn HOMOGENEOUS ss la la A 71 0 52 LA
2. Radial Distance Transversal Distance Figure 12 Envelope of the pulses presented in fig 10 option Instead only the line along the transversal direction which has the highest amplitude is calculated as shown in fig 13 Therefore Peak is a considerable faster option than Energy However Energy should be used when the simulations are to be compared with experimental results since it is the Energy which is normally measured when performing experiments Note that when simulating continuous waves the Peak option must be used The amplitudes of the peak plot are normalized so that the amplitude in the focal point is 0 dB when no attenuation is present Beampattern Peak 0 104 9 8 FSS 2 e Amplitude dB A gt a S gt 8 4 gt Transversal distance Figure 13 Example of Peak diagram Conditions are the same as in the Energy diagram of fig 11 April 8 1998 44 ver 2 1 ULTRASIM USER S MANUAL 6 1 2 Integrate Sidelobe Energy The third option in the Beampattern submenu Integrate Sidelobe En ergy is not yet fully tested but should nevertheless work under the following conditions An Energy simulation must be run first The selected axis in the Observation submenu must be phi The start value of phi must be 0 degrees and the end value should be 90 degrees e Integrate Sidelobe Energy must be selected immediately after per forming the Energy simulati
3. 113 64 lambda 1 Transducer aperture D 12 00 mm 27 27 lambda 2 elements No A 3 points P 1500 April 8 1998 21 ver 2 1 ULTRASIM USER S MANUAL The Transducer submenu when the TransducerGeometry flag is set to annular array is shown above The line Input is in mm units shows the value of the pitch mm flag while the wavelength lambda is calculated from the values of Frequency cf Excitation submenu and Speed of Sound cf Medium submenu Note that when the Medium flag is set to 2D Layered points is re placed by rays and two additional options are included See below Transducer Type can be either Equal Area default Equal Width Cir cular or User Defined Width Equal Area is an annular array transducer where all rings have the same surface area Equal Width is an annular array transducer where all rings have the same width Circular is a transducer consisting point sources spread around the perimeter of a ring User Defined Width is an annular array transducer on which the user may choose the width of each ring as he likes The user will be asked to make a choice only after a simulation is started Fixed Focus is the Radius of Curvature of the transducer and corresponds to the depth at which the beam will be focused if no electronic focusing is set Transducer aperture is the diameter of the transducer elements is the number of rings on the transducer or the number of point sources if
4. Apodization is explained in the previous subsection The remaining parameters refer to the focusing algorithm for calculating electronic time delays See the previous subsection for an explanation of Speed of Sound Transducer diameter and Radius of Curvature Calculation of Electronic Delays gives you the choice between the follow ing options 0 Focusing Algorithm 1 Focusing Algorithm with the addition of constant delays 2 User Defined Electronic Delays Choosing Focusing Algorithm tells UltraSim to use the focusing algorithm when calculating the electronic time delays Focusing Algorithm with the addition of constant delays also uses the fo cusing algorithm However you may add a constant time delay to each ele ment in addition to the delays calculated by the focusing algorithm When choosing this option a new option appears in the submenu 22 Constant delays el 1 5 ns transmit 00000 The above example is given for an annular array of 5 rings The first element of the delay vector gives the delay on element 1 on the transducer April 8 1998 30 ver 2 1 ULTRASIM USER S MANUAL which is the inner ring while the last element of the delay vector gives the delay on the outer ring When selecting the Constant delays option you must either enter the entire vector of delays in this example it is 5 elements don t forget to enclose the values in brackets or press lt CR gt for no chan
5. 1998 39 ver 2 1 ULTRASIM USER S MANUAL April 8 1998 40 ver 2 1 ULTRASIM USER S MANUAL 6 SIMULATIONS 6 1 Beampattern Beampattern simulates the ultrasound wave along a line in space or to be more correct the wave is simulated at points along a line The method which is used for the simulations is based on Huygen s principle of representing a source by point sources and adding the contribution from all point sources in order to get the resulting field The method for simulation in homogeneous material is described below This method is also the foundation for the simulation method in a layered medium which is looked into next 6 1 1 Simulation Method Homogeneous material Figure 8 Illustration of the beampattern simulation method The source is the lower surface and the beampattern is found along the upper line As is demonstrated in the above figure a pulse is sent from each trans ducer point at time tiransmit to Ati tpuise 2 where At is a time delay for all points on element i on the transducer tpuise is the duration of the pulse Thus UltraSim sets the transmit time to be the time when half the pulse is emitted The delays will be calculated from the setting of an electronic focus in the Beamforming submenu of the Configuration menu cf 4 5 and by selecting View Delays you can see the values of the delays Note also April 8 1998 41 ver 2 1 ULTRASIM USER S MANUAL that the pulse
6. 7 r r 2 o o 8 6 FEB 1995 16 01 3 o z 6f Frequency 3 5 MHz dB focus at 60 00 mm steered angles L L L L L L L 0 10 20 30 40 50 60 70 80 90 100 Inf periods rectangular pulse no delay quantization radius mm el 0 az 0 Figure 6 Intensity plot along acoustic axis for continuous excitation for array of Fig 3 April 8 1998 18 ver 2 1 ULTRASIM USER S MANUAL 4 CONFIGURATION This section gives a description of how to set up a configuration previous to performing a simulation If you are using UltraSim for the first time you are adviced to study this section thoroughly as knowledge of the UltraSim Configuration is a requirement for a correct interpretation of the simulation results You may however skip the sections marked Advanced unless you are planning to use the option s described in an Advanced section 4 1 SetFlags There are six submenus to the SetFlags menu with the following options Focus Mode Fixed Focus Default Dynamic focus TransducerGeometry Rectangular and Curved Array Default Annular Array Medium Homogeneous Default Layered 2D Layered 3D Coordinates Rectangular Default Spherical k space sin angle pitch mm mm Default pitch ref to lambda Observation Point Line Default Plane Plane gt Movie Volume Volume gt Movie 4 1 1 Focus Mode The Focus Mode flag should start in its default value Fixed Focus Setting
7. N 64 M 1 f 3 5 MHz pitch 0 5 osc Inf Azimuth no apodization Elevation no apodization BEAMWIDTH dB Aperture AZ 14 08 mm i L L L ie L 10 20 30 40 50 60 70 80 90 100 Range in mm Azimuth focus 60 mm Envelope Figure 3 Plot of beamwidth contours 6 12 and 20 dB for a 64 element array with half lambda pitch at 3 5 MHz focus 60 mm ARRAY RESPONSE Reference 38 96 us 6 FEB 1995 15 58 Theta 0 deg Phi 0 deg N 64 M 1 f 3 5 MHz pitch 0 5 osc 3 Azimuth no apodization Elevation no apodization View 3D default Weighted envelope DN o RESPONSE lin y oo 100 Aperture AZ d 14 08 mm Range in mm Azimuth focus 60 mr Figure 4 Plot of pulse in focus as sent from the same array as in Fig 3 Pulse form is 3 periods shaped with a cosine April 8 1998 17 ver 2 1 ULTRASIM USER S MANUAL Beampattern delays set for steering to fixed point source moves 0 T T T T 8 g 5 6 FEB 1995 16 06 4 oa o o S 10r Frequency 3 5 MHz J 20 25 30 35 dB focus at 60 00 mm steered angles 40 L L L 1 60 40 20 0 20 40 60 3 periods cosine pulse no delay quantization azimuth deg el 0 observed at 60 00 mm Figure 5 Beampattern obtained by summing energy over all time at a dis tance equal to geometric focus 60 mm Beampattern delays set for steering to fixed point source moves 10 r
8. Start depth of first focal zone mm 0 4 End depth of last focal zone mm 100 5 Apodization no apodization Parameters used in focusing algorithm 14 Speed of Sound c m s 1540 15 Transducer diameter D Real Transducer Diameter is used 16 Radius of Curvature ROC Real Transducer ROC is used 17 Focus mode 2way 18 Calculation of Electronic Delays Focusing Algorithm The first line in the submenu Dynamic focusing 2 way mode tells you the value of the Focus mode flag and the choice made on option 17 Focus mode The Focus mode options lets you choose to focus on Transmit Receive or both 2 way Dynamic focusing is not usually used on transmit due to loss of frame rate but it may be interesting to simulate the effect of two or three zones on transmit If you do two ways simulations both the transmitted and the received beam profile are plotted The sum of the dB versions of the two beams are presented in the same plot There are three ways to specify the dynamic focusing of annular array transducers In the first one you may set the number of electronic focal zones you want to spend You may also specify the minimum and maximum observation depth Ultrasim will spread the foci between these two depths This is done in a way that minimizes the phase aberrations In the second alternative you may add extra delays to the delays set by the automatic algorithm You can add one delay for each element These extra
9. element in and out of calculations centers is also a derived variable with the same syntax as elem_ pts except that it stores information about each element It is used as an input to the focusing and thinning calcualations Note that the length of centers is always less or equal to the length of elem_ pts C 3 3 Annular Array These parameters are set in t3usim m April 8 1998 68 ver 2 1 ULTRASIM USER S MANUAL d F theta tr off Type N elem N pts Array aperture Number of elements Number of points Fixed Focus Rotation angle Transducer offset Transducer type 0 egual area 1 egual width 2 circular elem pts is calculated in the function annular elem pts 1 x coordinates of transducer elem pts 2 y coordinates of transducer elem pts 3 z coordinates of transducer elem pts 4 element number 0 lt p lt P N length elem pts 1 C 4 Excitation The variable names in the tables are shortened so that e 1 means excita tion 1 C 4 1 Excitation transmitted signal f osc Fs MHz intfact Weig_numb e e 1 e 9 e 11 10 e 12 e 13 e 14 Frequency Number of oscillations in transmitted pulse Sampling frequency Time envelope of pulse 0 rectangular none 1 cosine Interpolation factor Pulse type Velocity of sound in delay calculations if osc inf then the excitation is continuou
10. the flag to Fixed Focus allows you to set an electronic focus to a point as described in section 4 5 The impact of setting the flag to Dynamic Focus is described in subsections 4 5 3 and 6 2 April 8 1998 19 ver 2 1 ULTRASIM USER S MANUAL 4 1 2 Transducer Geometry Setting the TransducerGeometry flag to Rectangular and Curved Array allows you to choose a rectangular or curved 1D 1 5D or 2D transducer in the Transducer submenu cf subsection 4 3 You may also choose to use an oval transducer With the flag set to Annular Array the transducer will be annular with an arbitrary number of rings In the Transducer submenu you are allowed to choose between Equal Area and Equal Width rings and two additional options which are described in subsection 4 3 4 13 Medium The Medium flag defines whether the medium used in the simulation is ho mogeneous or not You should generally use the default value Homogeneous unless you are particularly interested in examing wave propagation through layered media when you would want to use the Layered 2D or the Layered 3D option If you are using a Layered 3D medium you also must use one of the Beampattern simulations cf subsection 6 1 Using a Layered 3D medium will substantially increase the amount of time needed for a simula tion and should therefore be avoided unless necessary If you are using a Layered 2D medium time consumption will not be a problem However the Layers simulati
11. Error Phase centers plots the phase centers of the elements in three plots when a rectangular transducer is used The plots show the phase centers in the xy xz and yz planes There is only one plot for the annular array case the abscissa being the radial distance from the center of the transducer Exact delays shows the electronic time delays before they are quantized If the quantization of time delays is turned off Exact delays will give the delays that are used in the simulation Three plots are given as for the apodization The plot to the right shows the delays on the transducers surface while the two plots to the left shows the delays on transducer elements in the x and y directions Note that the plots to the left are plotted for y 0 and x 0 respectively Quantization Error gives three plots one plot of the exact time delays one plot of the time delays after they have been quantized and one plot of the relative quantizing errors The relative quantizing error lies within 0 5 0 5 April 8 1998 38 ver 2 1 ULTRASIM USER S MANUAL and gives the quantizing error relative to the worst quantizing error possible at the given sampling frequency Note that the values on the abscissa are pointers to where the transducer points are stored in the internal UltraSim variable This may be confusing when the points are not stored elementwise In fact the points are stored elementwise for the 1D linear array only April 8
12. L degaard Phase aberration correction in medical ultrasound imag ing Dr Ing dissertation Norwegian Institute of Technology 1996 14 K Epasinghe and S Holm Simulation of 3D acoustic fields on a con current computer Proc Nordic Symp in Physical Acoustics Ustaoset Norway Feb 1996 April 8 1998 58 ver 2 1 ULTRASIM USER S MANUAL A INSTALLATION The program requires Matlab version 4 2 or later and the Signal Processing Toolbox It also runs under Matlab version 5 It will run under UNIX Windows and Macintosh A 1 System Installation of ULTRASIM It is recommended to install ULTRASIM as a toolbox under the main matlab directory from now on called MATLABHOME ULTRASIM files must be installed in directories as specified These di rectories are e MATLABHOME toolbox ultrasim Files for setup and startup directory specified by ULTRASIMHOME variable e MATLABHOME toolbox ultrasim bp Files for Calculations Beam Pattern menu e MATLABHOME toolbox ultrasim coarray Files for Calcula tions Coarray tools menu e MATLABHOME toolbox ultrasim config Files for control of configuration window and menu e MATLABHOME toolbox ultrasim doc Files containing docu mentation and file header e MATLABHOME toolbox ultrasim list Files for generating out put of parameters e MATLABHOME toolbox ultrasim pe Files for Calculations 2D Response menu e MATLA
13. Transducer type is set to Circular see above points refers to the number of points used to represent the transducer when simulation methods Beampattern and 2D Response are used cf subsections 6 1 amp 6 2 The points are distributed over the transducer s sur face on a hexagonal grid Using sufficent number of points is important for the reliabilty of the results while choosing too many points will lead to an unnecessarily long computation time The optimal number of points to use depends on the frequency and the observation configuration Increasing the frequency and observing far from focus will require more points while low frequencies and observation in focus reduce the number of points required to perform a reliable simulation As a rule of thumb the points should be separated by approximately half a wavelength unless when observing close to focus when the points may be reduced and when observing at extreme regions in the extreme near field or very far from the beam center when the points should be increased When quitting the Transducer submenu the point separation in mm and wavelength is given as in this example point distance x 0 2459 mm 0 479 lambda y 0 2129 mm 0 4148 lambda April 8 1998 22 ver 2 1 ULTRASIM USER S MANUAL 4 3 2 Rectangular and Curved Array TRANSDUCER SUBMENU RECTANGULAR AND CURVED ARRAY Input is in mm units lambda 0 44 mm 18 Transducer type 0
14. an error message and a proper return from the routine April 8 1998 63 ver 2 1 ULTRASIM USER S MANUAL 11 The file h txt should always be included in the heading of new ULTRA SIM m files B 2 Responsibilities for files Administration of changes in files especially the file usimenf m should be carefully planned Sverre Holm is responsible for usimenf m and all changes to this file Other users may change this file too BUT they should send an email which explicitly states what changes are done to sverreQifi uio no who is respon sible for mailing a copy of latest updates of usimcnf m to all users of UL TRASIM List of ULTRASIM contacts e Department of Informatics University of Oslo sverreQifi uio no e Department of Biomedical Eng University of Trondheim larso ibt unit no e Vingmed Sound Horten tkl vingmed no Responsibility for the different modules are as follows Beam Pattern Lars degaard Sverre Holm 2D Response Sverre Holm layers Lars degaard Annular Array Sverre Holm usimenf Sverre Holm All changes concerning ULTRASIM should be reported to sverre ifi uio no in order for this document to be updated April 8 1998 64 ver 2 1 ULTRASIM USER S MANUAL C ULTRASIM VARIABLES C 1 Introduction This appendix describes the main parameters used for storing setups It is intended primarily for those who would like to modify or develop their own functions for Ultrasim The setup of a simu
15. by USER ULTRASIMHOME and two sub directories cnf and results must be created The cnf directory is used as a default location for configuration setup files and the results directory is used for storage of results during movie simulations The results directory is also used for storage of default parameters for some of the programs A 3 PC Installation The path to MATLABHOME toolbox ultrasim can be set either in mat labrc m or in startup m The file userusim m must be copied from MATLABHOME toolbox ultrasim user to MATLABHOME toolbox ultrasim Apart from this there are no differences from a UNIX installation The path separator is automatically changed to in all filenames A 4 Setup for Developing your own Functions If the user wants to develop new functions or refine existing ones a parallel directory to the installation directory under ULTRASIMHOME should be April 8 1998 61 ver 2 1 ULTRASIM USER S MANUAL created under USER ULTRASIMHOME The path must be set in userusim m so that this directory comes before the installations directory see commented examples in the file In this way it is possible to have your own versions in the development phase April 8 1998 62 ver 2 1 B 1 10 ULTRASIM USER S MANUAL PROGRAMMING Advice for ULTRASIM programming All variables are represented in meter seconds Hz etc although they may be displayed in mm ms microsec etc Upw
16. changed This April 8 1998 37 ver 2 1 ULTRASIM USER S MANUAL works well for the transducers where the points are distributed on a rectan gular sampling grid rectangular and curved arrays The transducers where the points are distributed on a hexagonal grid annular arrays will not be as smooth as desired in all cases 5 6 Apodization This option makes three plots describing the apodization The rightmost plot gives the apodization over the transducers surface while the two plots to the left gives the apodization along the azimuth and elevation directions If a 1 D transducer is specified only the upper left hand figure will appear Note that a special case occurs when the equal area annular transducer is selected UltraSim will automatically set an apodization on each ring to compensate for the fact that there are an unequal number of points on the rings due to the fact that when UltraSim spreads the points on the trans ducer s surface more consideration are taken to get an equal spacing between the points than to get exactly the same number of points on each ring To get an example of this phenomenon select the equal area annular transducer and turn the apodization off before selecting View Apodization Note that as the number of points used to represent the transducer increases the importance of this apodization decreases 5 7 Delay The Delay option has three submenus Phase centers Exact delays and Quantization
17. nevertheless be used when printing a hardcopy Also note that the font Symbol gives greek letters The Move and Rotate options may be toggled on or off A black square to the left of the corresponding item in the Text menu indicates that the option is on Note that activating any of the two options will automatically turn the other one off When one of these options are on you may move or rotate any text object by selecting it with the mouse and holding the left mouse button down until you have moved or rotated the object to the position you choose April 8 1998 55 ver 2 1 ULTRASIM USER S MANUAL April 8 1998 56 ver 2 1 ULTRASIM USER S MANUAL 8 REFERENCES References 1 P R Stepanishen Transient radiation from pistons in an infinite planar baffle J Acoust Soc Am 49 5 pp 1629 1638 February 1971 2 A Penttinen and M Luukkala The impulse response and pressure nearfield of a curved ultrasonics radiator J Phys D Vol 9 pp 1547 1557 1976 3 M A Fink and J F Carduso Diffraction effects in pulse echo mea surement IEEE Trans Sonics Ultrason vol SU 31 pp 313 329 July 1984 4 J A Jensen and N B Svendsen Calculation of pressure fields from arbitrarily shaped apodized and excited ultrasound transducers IEEE Trans Ultrason Ferroelec Freq Contr vol 39 no 2 pp 262 267 March 1992 5 D H Johnson and D E Dudgeon Array Signal Processin
18. rectangular 2 elliptic 0 17 Radius of curvature 0 planar lt 0 curved 0 00 mm 0 lambda AZIMUTH 1 Azimuth array aperture d 12 00 mm 27 27 lambda 2 Azimuth elements Ne_az 4 3 Azimuth points per element Np az 1500 ELEVATION 1 D 5 Elevation array aperture a 6 Elevation elements Me el 1 7 Elevation points Mp_el 10 9 Elevation Fixed focus ri F 50 00 mm 113 64 lambda Above is the Transducer submenu when the TransducerGeometry flag is set to Rectangular and Curved Array Note that when Elevation elements is set to 3 or 5 the transducer will be a 1 5D transducer which is described in the below subsection Transducer type is by default rectangular p 0 Entering a at the prompt gives the options The footprint can be set by changing the parameter p in the equation for the footprint EE a AN For negative values of p an octagonal shape can be chosen p 8 Radius of curvature is used to define a radius of curvature for a curved array by setting a negative value ie for obtaining a convex array A positive value gives a prefocused concave transducer in the azimuth direction i e sets the focal point in the xz plane Azimuth array aperture is the length of the array in the azimuth x di rection Azimuth elements allows you to set the number of transducer elements in the azimuth direction Azimuth points per element refers to the number of points used to
19. rep resent the transducer when simulation methods Beampattern and 2D Re sponse are used cf subsections 6 1 amp 6 2 See the description of this item in the transducer submenu for annular arrays the above subsection Note April 8 1998 23 ver 2 1 1 00 mm 2 27 lambda ULTRASIM USER S MANUAL that the total number of points on the transducer is calculated as Azimuth elements Azimuth points per element Elevation points Elevation array aperture is the length of the array in the elevation y direction Elevation elements allows you to set a desired number of transducer elements in the elevation direction By setting Elevation elements to 1 you will get a 1D array while setting it to 2 4 6 or higher gives you a 2D array with equal size elements in both directions Note that 3 and 5 elements are reserved for the special case of a 1 5D transducer where the elements may be of different size Elevation points denotes the number of points used to describe the transducer when performing the Beampattern and 2D Response simu lations See the above comments to Azimuth points per element Note that unlike the azimuth equivalent Elevation points holds the total points for all the elevation elements and not on each of the elements This has been necessary in order to include 1 5D arrays see below the elements of which may have different elevation apertures Elevation Fixed focus allows
20. understand the properties of transducers of more complex shapes such as oval or elliptic ones and to find the fields generated by 2 dimensional transducers For this reason Ultrasim a general purpose simulator tool has been made This chapter is adapted from 11 3 2 Method and Examples In order to find the field it is common to assume that the Rayleigh integral applies where the velocity potential is given by the normal velocity integrated over the active surface The source is assumed to be plane i e the lateral dimensions and the radius of curvature are large compared to the wavelength 2 and thus curved transducers used in ultrasound are covered by this as sumption In the impulse response method the Rayleigh integral is converted from a 2 dimensional to a 1 dimensional integral 1 This assumes that the diffrac tion impulse response has been derived for the transducer shape used In the described simulator this method is not used One of the reasons is that it is desirable to be quickly able to analyze new transducer shapes This could also be done using the impulse response method by subdividing the radiat ing plane into smaller basic subtransducers with a known diffraction impulse response 4 However it is also desirable to be able to analyze the field in an April 8 1998 15 ver 2 1 ULTRASIM USER S MANUAL inhomogenous medium One of the underlying assumptions of the impulse response method is that the path
21. you may also choose to observe along a line which is also the only possible option when performing a beampattern simulation cf subsection 6 1 Observation in a plane or volume and time varying observations in a plane or volume movie is only possible when conducting a 2D response simulation cf subsection 6 2 See also subsection 4 7 for more details 4 2 Configuration Submenus General The remaining subsections of this section concentrate on the submenus of the Configuration menu With the exception of List all the Configuration submenus control one part each of the configuration necessary for running a simulation All the submenus are displayed in the Matlab text window and they all display the parameters on the same format with the exception of the Medium submenu for the layered medium No Parameter Name Value The Transducer submenu which is given below is a typical example To change the value of one parameter type the No which is preceding the parameter name at the input prompt When you have made the changes you want to do simply press lt CR gt Enter to exit the submenu The No is the array index in the variable for this menu except for the Observation menu see appendix for more details 4 3 Transducer Parameters 4 3 1 Annular Array TRANSDUCER SUBMENU ANNULAR ARRAY Input is in mm units lambda 0 22 mm 18 Transducer type Equal Area 9 Fixed focus F 50 00 mm
22. you to set the focal point in the elevation direction i e the focal point in the yz plane 4 4 Excitation Parameters The excitation submenu with its default values looks like this EXCITATION SUBMENU 1 Frequency 7 00 MHz 9 Transmitted pulse length oscillations 0 0 10 Pulse Weighting none 0 cosine 1 0 11 Sampling frequency Fs 100 00 MHz 12 Quantizing of Time Delays i Off 13 Pulse Type Ultrasim CHANGE number gt Decision lt CR gt exit Frequency is the center frequency of the emitted signal Transmitted pulse length is the number of periods of a Pulsed Wave PW By setting this parameter to 0 or to Inf which is the Matlab symbol for infinite a Continuous Wave CW will be used in the simulations Note that April 8 1998 24 ver 2 1 ULTRASIM USER S MANUAL some simulations will require a PW emission namely the Layers simulation and the Energy simulation in the Beampattern submenu cf section 6 1 Pulse Weighting applies only to the PW case and the emitted pulse will have a cosine envelope if it is set to 1 The emitted pulse with a cosine envelope corresponds reasonably to the pulses emitted from a real transducer No envelope is added to the PW signal when Pulse Weighting is set to zero Sampling Frequency is used for quantizing the electronic focusing time delays It is described below If Quantizing of Time Delays is On the the electr
23. ANGULAR 2 1 axis x 3 Start value of x mm 15 4 End value of x mm 15 5 2 axis Ly 6 Start value of y mm 10 7 End value of y mm 10 April 8 1998 48 ver 2 1 ULTRASIM USER S MANUAL 12 3 axis a 13 Start value of z mm 10 14 End value of z mm 25 10 Start value of t us 12 99 11 Stop value of t us 15 25 8 plots will be produced for movie 15 4 obs pts mn 8D CHANGE number gt Decision lt CR gt exit 6 3 2 Slice Plot The volumetric simulations area is visualized using the SLICE function in MATLAB The results are plotted in ULTRASIM PLOT window and the SLICE plots are called by CALCULATIONS gt 2D RESPONSE gt SLICE PLOT in ULTRASIM CONFIGURATION CALCULATION window Set the following plot options gt envelope rf e r gt linear logarithmic lin log Observation slices for X Axis Modify slices y n y gt Background display y n y Range for the axis X 15 to 15 Enter the number of slices default 0 max 5 1 Axis X slice 1 Enter value gt 0 Observation slices for Y Axis April 8 1998 49 ver 2 1 ULTRASIM USER S MANUAL Modify slices y n y gt Background display Ly n y Range for the axis Y 10 to 10 Enter the number of slices default 0 max 5 1 Axis Y slice 1 Enter value gt 0 gt Range Movie on Third axis y n y Range for Axis Z 10 to 25 Enter start value 15 En
24. BHOME toolbox ultrasim plot Files for control of plot tool window e MATLABHOME toolbox ultrasim toolbox General tools for menus date etc e MATLABHOME toolbox ultrasim txt Files with text string information for use in menus e MATLABHOME toolbox ultrasim user Files that the user should copy to his own matlab directory April 8 1998 59 ver 2 1 ULTRASIM USER S MANUAL e MATLABHOME toolbox ultrasim view Files for View menu e MATLABHOME toolbox ultrasim annulus Files for Calcula tions Analys menu e MATLABHOME toolbox ultrasim aberra3d Files for Calcu lations Beam Pattern menu when a layered medium is specified e MATLABHOME toolbox ultrasim aberrati Files for Calcula tions Layers menu e MATLABHOME toolbox ultrasim optimize Files for optimiza tion of thinned arrays e MATLABHOME toolbox ultrasim anneal Files for optimiza tion of thinning using simulated annealing e MATLABHOME toolbox ultrasim 1point5 Files for setup of 1 5 D arrays e MATLABHOME toolbox ultrasim cnf elec Setup files for Ul trasim examples e MATLABHOME toolbox ultrasim cnf_ mech Setup files files for site specific examples These directories will automatically be generated if unzip ultrasim zip is run in the directory MATLABHOME toolbox The names of these directories are specified in usiminit m which is the only installation dependent file There are thre
25. Parameters The Observation submenu with its default values is as following when the observation flag is set to Line default OBSERVATION SUBMENU Linetype LINE Coordinates RECTANGULAR 1 pixels along one axis 90 2 Selected axis y 3 Start value of y mm 0 4 End value of y mm 30 5 Fixed value of x m 6 Fixed value of z mm 100 us 7 Fixed value of t April 8 1998 32 ver 2 1 ULTRASIM USER S MANUAL Linetype and Coordinates which are unsettable in this menu show the values of the flags set in the Set Flags submenus Obviously the Obser vation submenu will change if these flags are altered Changing the Co ordinates flag to Spherical will not only have the effect of changing the coordinates from xyz to r theta amp phi but will also alter the shape of a line if this is the Observation option selected see below Note that rectangular coordinates must be used if you have chosen the Observation option Plane pixels along axis refers to the resolution of the line Increasing pixels will increase the resolution which also will increase computation time of the simulation Obviously this option becomes redundant when choosing a Point as Observation option Also this option is replaced by 15 obs pts mm 1 when the observation option is a Plane This is just another way to define the resolution Selected axis can be x y or z and it refers to the axis to which
26. UNIVERSITY OF OSLO Department of Informatics ULTRASIM User s Manual ver 2 1 Program for Simulation of Ultrasonic Fields Sverre Holm Frode Teigen Lars degaard Vebj rn Berre Jan Ove Erstad Kapila Epasinghe Research Report 1996 220 ISBN 82 7368 133 5 ISSN 0806 3036 April 8 1998 ULTRASIM USER S MANUAL Contents 1 INTRODUCTION 1 1 About Ulfrrasim 1 2 About Matlab 1 3 About this document 1 4 History 1 5 Getting started 1 6 How to set thecoordinates 2 TUTORIAL 2 1 Example 1 Beam pattern in focus 2 2 Example 2 On axis field 2 3 Example 3 2D response pulsed grating lobes 2 4 Example 4 2D response continuous wave 2 5 Example 5 2D response moving pulse 2 6 Benchmark calculation 3 SIMULATION OF ACOUSTIC FIELDS 3 1 Introduction 3 2 Method and Examples 4 CONFIGURATION 4 1 SetFlags 4 1 1 Focus Mode 4 1 2 TransducerGeometry 4 13 Medium 4 1 4 Coordinatesandpitch mm 4 1 5 Observation 4 2 Configuration Submenus General 4 3 Transducer Param
27. VERED ge ed ad ED Bee A SEE ra 71 C 6 Observation points sources 71 C 7 Dependent parameters 73 C 8 Administrationparameters 73 C 9 Temporary variables convention 73 Document History ver 1 0 16 March 1995 Combined Programmer s Guide and User s Guide into a single document and added description of annular array design and 2D response ver 2 0 15 August 1996 Moved advanced functions to separate document General update added tutorial introduction ver 2 1 7 April 1998 Updated installation instructions Added volumetric simulation and visualization Copyright 1996 1998 April 8 1998 5 ver 2 1 ULTRASIM USER S MANUAL April 8 1998 6 ver 2 1 ULTRASIM USER S MANUAL 1 INTRODUCTION 1 1 About Ultrasim UltraSim is a Matlab toolbox for ultrasound wave simulation developed by Vingmed Sound VMS Horten Norway Department of Physiology and Biomedical Engineering IFBT and Department of Mathematical Sciences IMF Norwegian University of Science and Technology Trondheim and Department of Informatics IFI University of Oslo UltraSim serves as a standard platform for simulation programs concerning ultrasonic imaging systems UltraSim provides a tool for transducer and dome design and will increase the user s understanding of acoustic wave propagation in homoge neous and layered media UltraSi
28. a LINE with variation along sind axis 2rh a PLANE with fixed and t ie variation parallel tor and 0 3xt a VOLUME with fixed y and z ie variation parallel to x and t MXZ MOVIE in x z plane fxt VOLUME MOVIE in x t plane means that this value may be anything Anyone of the rectangular coordinates x y z t may be substituted with any one of the other rectangular coordinates and likewise with the other coordi nate systems The convention for labelling of the axes is given below x y z t rectangular coordinates time x y Zz or time axis r h p t spherical coordinates time r 0 6 or time axis r e s t spherical coordinates time r sind sind or time axis C 3 Transducer C 3 1 Transducer flag The interpretation of the transducer vector depends on the setting of the transducer flag geometry flag flagg 2 1 Rectangular and curved array 2 Not Applicable 3 Annular Array C 3 2 Rectangular and Curved Arrays These parameters are set in tlusim m Note that in this and subsequent tables the variable names are shortened t 1 is equivalent to transducer 1 April 8 1998 67 ver 2 1 ULTRASIM USER S MANUAL d a tl Array aperture azimuth dimension ak t 4 Azimuth kerf not used N elem az t 2 Number of elements in azimuth dimension N pts az t 3 Number of points in azimuth dimension ROC t 17 Radius of Curvature Azimuth Fixed Focus spher
29. ards compatibility Write m files as functions in order to limit memory requirements and due to easiers loading saving of configurations and shorter function calls Limit the number of variables in the workspace That is use a variable excitation instead of the variables f r foc_ theta etc The reason is to limit memory requirements Use one vector of parameters to describe each of a The physical geometric characteristics of the TRANSDUCER b The EXCITATION of the transducer characterization of the trans mitted signal The beamforming parameters apodization elec tronic steering focusing is also included in the EXCITATION vector c The observation OBSERVASJON points ie where to calculate radiation intensity d The characteristics of the medium MEDIA e g speed of sound No use of global variables Parameters in the menus should not depend upon each other Under no circumstances should an excitation parameter depend on for instance a transducer parameter Exception from this rule exist in the 1 5D curved elliptic array menu for the parameters a ai am ao and Q All such exceptions must be stated explicitly in this manual The reason for this is to limit the complexity of the menus The letters i and J are dedicated to y 1 Max 8 letters in filenames for compatibility with PC Every configuration which is not supported should be documented e g by
30. city in the medium cf subsection 4 6 Normally Speed of Sound should not be changed from its default value 1540 m s which is an approximate average speed of sound in human tissue 4 5 2 Additional focusing algorithm parameters Advanced You will get the following two options if your Medium and Transducer Geometry flags are set to Layered 2D and Annular Array respectively 15 Transducer diameter D Real Transducer Diameter is used 16 Radius of Curvature ROC Real Transducer ROC is used Like Speed of Sound which is commented on in the above subsection these parameters refer to the values used in the focusing algorithm 8 and they should normally equal the actual transducer diameter and radius of curvature which are set in the Transducer Submenu cf subsection 4 3 4 5 3 Dynamic Focus Advanced The current version of UltraSim supports dynamic focus only when the Medium and TransducerGeometry flags are set to Layered 2D and An nular Array respectively or when the em 2D response calculation is used with April 8 1998 28 ver 2 1 ULTRASIM USER S MANUAL rectangular arrays When the Focus mode flag is set to Dynamic Focus you will get the following Beamforming submenu BEAMFORMING SUBMENU Dynamic focusing 2 way mode Receive 19 Number of focal zones 0 20 Start depth of first focal zone mm 21 End depth of last focal zone mm 0 o Transmit 2 Number of focal zones 0 3
31. d in o usim m are xmin ymin zmin t start xmax ymax zmax t_ stop resolution E w OT E D gt gt OA OA OO AA ES start point 1 coordinate x r start point 2 coordinate y 0 sind start point 3 coordinate 2 0 sing start point time stop point 1 coordinate x r stop point 2 coordinate 9 0 sind stop point 3 coordinate z sing stop point time of points along ONE axis used in Beam Pattern 3 point for def of a general plane 1 coordinate 3 point for def of a general plane 2 coordinate 3 point for def of a general plane 3 coordinate 3 point for def of a general plane time Tells how to interpret the above coordinates l x y z 3 r 0 6 4 r sind sing points per mm only used by 2D Response where o 15 c is time step in movies NB Generalized plane 3 points is not yet implemented ie observasjon 10 13 x y Z t are derived variables that contain the coordinates of the obser vation points field points SYNTAX of x y z t Asa rule x y z and t are to be interpreted as x x coordinates of the observation points field points y y coordinates of the observation points field points z z coordinates of the observation points field points t time coordinates of the observation points field points An important exception from this rule is when r Inf then Inf ON lt x coordinates of the observatio
32. d the delays on all transducer elements To use the original entries of a row simply press lt CR gt and enter 0 when you have reached the desired number of rows i e focal zones 4 6 Medium Parameters The Medium submenu defines the characteristics of the medium through which the acoustic wave propagates The submenu for a homogeneous medium is fundamentally different from the submenu for the 2D amp 3D layered medium and it will be adequate to treat the two submenus separately April 8 1998 31 ver 2 1 ULTRASIM USER S MANUAL 4 6 1 Homogeneous Medium When the Medium flag is set to Homogeneous the Medium submenu looks like this MEDIUM SUBMENU Model HOMOGENEOUS 1 Speed of Sound c 1540 2 Impedance Z 0 MRayl 3 Attenuation alpha alpha 0 000 1 m MHz 4 Attenuation beta beta 0 000 The Speed of Sound is the propagation velocity of the acoustic wave in the homogeneous medium The default value of 1540 m s corresponds to an approximate average speed of sound in human tissue The Impedance is not used in the current version of UltraSim The Attenuation parameters alpha and beta are only used by the func tions Spectrum with depth in the View menu and the Annular Array Analysis menu and they are used to calculate the frequency dependent attenuation according to the equation I r Lo Note that alpha is given in dB cm MHz See subsection 5 2 for details oa tr 4 7 Observation
33. ded unless some precautions are taken and unless you are familiar with Matlab as loading a result file will replace the contents of variables having the same name as the variables in the result file Also you must save the results immediately after a simulation before making any changes to the configuration for the above procedure to be useful You can recognize a file saved by Save results by its res mat extension 7 2 Axis The Axis menu allows you to change the axis properties The following options are available e Axis Off On turns the axis on or off depending on the current state e X Axis Y Axis and Z Axis allows you to change any of the three axes to a linear or logarithmic scale depending on the current scale of the axis e Format controls the format of the axes normal is the default format which implies that the limits of the axes are set to the minimum and maximum values of the data plotted equal readjusts the axes so that proportions are right i e a circle will indeed look like a circle when plotted which is not necessarily the case with the normal format square produces square axis i e the x and y axes have the same physical length Note that setting the format to normal will turn of both the equal and the square format while the last two formats do not interfer with each other i e setting the format to square does not set or unset the equal format e Zoom allows you to zoom in to or out of t
34. delays are constant for all observation depths It is thus possible to correct for phase aberrations caused by the dome The third alternative is a manual April 8 1998 29 ver 2 1 ULTRASIM USER S MANUAL specifications of the positions and the delays of each zone which allow you to set the delays as in a scanner The menu s options will be adjusted according to the choice of Focus mode as will become clear from the description below Following Receive there are three parameters that define the receive focusing Obviously these become redundant when Transmit is chosen as Focus mode and they also are omitted when Calculation of Electronic Delays is set to Manual see below Likewise the transmit parameters are not included in the submenu when Receive is chosen as Focus mode or when Calculation of Electronic Delays is set to Manual Number of focal zones gives the number of zones to which UltraSim sets a focal point Note that you will get ideal focusing to every observation point if you set this parameter close to infinite Start depth of first focal zone and End depth of last focal zone define the region over which the focal zones will be equally distributed Note that if you set the start depth equal to the end depth and Number of focal zones to 1 you get the fixed focus case This procedure will be useful and necessary if you want to set a fixed focus when transmitting and use a dynamic receive focus
35. during the selected time interval For most practical tasks it suffices to relate the time to the fixed z value so that Start value of t is set to z c tpuise 2 and End value of tis set to z c tpuise 2 See also the above comments to figure 7 April 8 1998 34 ver 2 1 ULTRASIM USER S MANUAL 4 8 Thinning and Weighting The option for Array thinningcontains functions for thinning and per turbing an array as well as placing elements with spacing determined by a geometric series When asked to input numbers this must be done in the MATLAB command window A local symmetry flag is indicated by ON OFF and is altered by pushing the x button When ON the thinning will remove elements symmetrically around the array origin The option Optimize weights will give the optimal apodization for the current array Optimality is defined in the Chebyshev sense i e constant sidelobe level The apodization weights are put into the global matrix vari able amp ud User defined apodization User operation is performed by pushing mouse buttons or a key on the keyboard while pointing inside the UltraSim configuration window The first function uses the formulation of the Parks McClellan Remez algorithm and thus can optimize equi spaced ar rays For these arrays it will be the most efficient one to use Input value is the angle where the sidelobe level is desired to be reached in degrees A second routine uses a generalized Remez algorithm form
36. e lines that need to be edited in this file 1 Set ULTRASIMHOME to the directory where you have placed the ultrasim directories This directory should be under the toolbox direc tory of the matlab installation directory MATLABHOME toolbox Examples can be found in the file 2 The local command for text printing should be set in the printeremd variable This affects the Configuration List command Example printercmd print 3 On a UNIX system the local command for on line display of the docu mentation by the Help User documentation command should be set in the variable doc_ command Examples April 8 1998 60 ver 2 1 ULTRASIM USER S MANUAL doc command xdv1 doc command ghostview doc command acroread A 2 User Installation UNIX The steps a user must undertake to start using Ultrasim are 1 Each user must have a path to ULTRASIMHOME If it is not set globally it can be set in startup m in the user s matlab directory An example p path path p local matlab toolbox ultrasim 2 Each user must have a file userusim m in his matlab directory typ ically user name matlab userusim m This file can be copied from the user directory 3 In the userusim m file the path for result files and configuration files are set by the variable USER ULTRASIMHOME which typically should be USER ULTRASIMHOME user_name matlab ultrasim 4 The directory specified
37. e t 18 overall shape 0 rectangular 2 elliptic a b t 5 Array aperture in elevation dimension M_elem_el t 6 Number of elements in elevation dimension M_pts_el t 7 Number of points in elevation dimension ri F t 9 Focal length in elevation dimension bk t 8 Elevation kerf not used t 10 t 16 Reserved for 1 5 D arrays The number of elevation elements t 6 is used to specify a 2D array with equal elements in the elevation dimension when t 6 gt 1 For the special case of t 6 3 or t 6 5a 1 5 D array is meant Refer to Advanced User s Manual for documentation elem_ pts is a derived variable that contains information about each point on the transducer surface It is the main input for all field simulation routines elem pts 1 x coordinates of transducer elem pts 2 y coordinates of transducer elem pts 3 z coordinates of transducer elem pts 4 nn azimuth element number 0 lt nn lt P elem pts 5 mm elevation element number 0 lt mm lt Q N length elem pts 1 Special interpretations of elem_pts 4 and elem_pts 5 e Klement number is 0 Element is not included in calculations This feature is used for permantently eliminating points and is used when a footprint other than rectangular is specified e Element number is negative Element is not included in calculations This feature is used for thinned arrays and makes it easy to toggle the
38. equivalent to the same items on the Configuration window menubar and are briefly commented in sub section 1 5 Y ULTRASIM PLOT File Axis Options Text Print Clear Subplot Colormap Shading Figure 14 The UltraSim Plot window 7 1 File There are two items in the File menu e Save Results e Load Results Works for Beampattern simulation results only Save Results allows you to save the results from a simulation The results can be loaded at a later stage to reproduce the graphical output of the Plot window This is obviously done by choosing Load Results Note that Load Results will only produce a graphical output and not alter the contents of the variables in which your configuration is stored Presently Load Results will only work for results that are saved after one of the simulations found in the Beampattern submenu April 8 1998 53 ver 2 1 ULTRASIM USER S MANUAL Not only the variables needed to reproduce the graphical results are saved when Save Results is invoked but also all the other variables defined by UltraSim or by yourself will be saved This has been done in order to facilitate the documentation of saved results s all configuration variables are saved you can verify what configuration was used to produce the results by loading the entire save file by typing load lt filename gt in the text window and then watch the settings of the configuration menu Note that this procedure is not recommen
39. eters 4 3 1 Annular Array 4 3 2 Rectangular and Curved Array 4 4 Excitation Parameters 4 4 1 Pulse Type Advanced 4 5 Beamforming Parameters 4 5 1 Fixed Focus 4 5 2 Additional focusing algorithm parameters Advanced 4 5 3 Dynamic Focus Advanced 4 6 Medium Parameters 4 6 1 Homogeneous Medium 13 13 13 13 13 14 14 15 15 15 April 8 1998 3 ver 2 1 ULTRASIM USER S MANUAL 4 7 Observation Parameters 32 4 7 1 How to set time when observing in a plane 33 4 8 Thinning and Weighting 35 4 9 ee 35 5 VIEW 37 5 1 Excitation transmitted signal 37 5 2 Spectrumwithdepth 37 5 3 Observation 37 54 Media 37 5 5 Transducer 37 5 6 Apodization 38 5 7 Delay 38 6 SIMULATIONS 41 6 1 Beampattern 41 6 1 1 Simulation Method Homogeneous material 41 6 1 2 Integrate Sidelobe Energy 45 6 2 2DResponse 46 6 2 1 Observation Plane 46 6 2 2 Compute Response 46 6 2 3 Surface
40. from the radiator to the summation point is independent on actual position Thus this method has limitations when the field is to be found in an aberrating medium In this case one has to give up the speed advantage and solve the Rayleigh integral directly tak ing the medium properties into account for each path from source to field point 8 9 The Rayleigh integral is solved by discretizing the radiating surface as suming that the plane source vibrates in a single mode thickness mode 3 and thus that the surface velocity is separable alt st Or cult The observation plane is also discretized and the integration is done by finding the distance and quantized time delay 7 from each source point to each of the observation points The time waveform is either continuous wave or a pulse that resembles the pressure pulse measured at the focal point on the acoustical axis At this point one will get coherent summation of the Rayleigh integral This means that we excite with a measured approximation of the surface velocity The following four figures give examples of the output from the simulator In addition it is possible to generate animations of travelling ultrasound pulses using the display of Fig 4 or to take the maximum at all locations of an animation and generate a contour plot like in Fig 3 April 8 1998 16 ver 2 1 ULTRASIM USER S MANUAL ARRAY RESPONSE Reference 38 96 us 6 FEB 1995 15 51 Theta 0 deg Phi 0 deg
41. g Concepts and Techniques Prentice Hall 1993 6 B A J Angelsen Waves Signals and Signal Processing in Medical Ultrasonics vol I and II Department of Physiology and Biomedical En gineering Norwegian University of Science and Technology Trondheim 1996 7 S Holm and K Kristoffersen Analysis of worst case phase quantization sidelobes in focused beamforming IEEE Trans Ultrason Ferroelec Freq Contr vol 39 no 5 pp 593 599 September 1992 8 L degaard S Holm and H Torp Phase aberration correction ap pled to annular array transducers when focusing through a stratified medium in Proc IEEE Ultrasonics Symp Nov 1993 Baltimore MD 9 L degaard S Holm F Teigen and T Kleveland Acoustic field sim ulation for arbitrarily shaped transducers in a stratified medium in Proc IEEE Ultrasonics Symp Nov 1994 Cannes France 10 J O Erstad and S Holm An approach to the design of sparse array systems in Proc IEEE Ultrasonics Symp Cannes France Nov 1994 April 8 1998 57 ver 2 1 ULTRASIM USER S MANUAL 11 S Holm Simulation of Acoustic Fields from Medical Ultrasound Trans ducers of Arbitrary Shape Proc Nordic Symp in Physical Acoustics Ustaoset Norway Jan 1995 12 S Holm and B Elgetun Optimization of the beampattern of 2D sparse arrays by weighting in Proc IEEE Ultrasonics Symp Seattle Wash ington Nov 1995 13
42. g 3 6 2 5 Color encoded This option is an alternative to the Contour option and shows the level in different colors instead 6 3 Volumetric Visualization This section explains the setting up of visualization parameters for volumetric simulations Visualization is done by using MATLAB SLICE routines 6 3 1 Observation Observation flag is set to either Volume for observation in x y z or x y t volume or Volume Movie for x y z t volume Observation parameters are set choosing CONFIGURATION gt OBSERVATION from the CONFIGURA TION window of ULTRASIM When observation flag is set to VOLUME the observation parameters are set as below OBSERVATION SUBMENU Option VOLUME Coordinates RECTANGULAR 2 1 axis x 3 Start value of x mm 15 4 End value of x mm 15 5 2 axis Ly 6 Start value of y mm 10 7 End value of y mm 10 April 8 1998 AT ver 2 1 ULTRASIM USER S MANUAL 12 3 axis SO 13 Start value of z mm 10 14 End value of z mm 25 9 Fixed value of t us 12 99 15 obs pts mm 2 CHANGE number gt Decision lt CR gt exit The first and the second axes are fixed while the third axis can be either zort 1 z 2 t Select a menu number When observation flag is set to VOLUME gt MOVIE the observation parameters are set as below OBSERVATION SUBMENU Option VOLUME movie Coordinates RECT
43. ge User Defined Electronic Delays allows you to freely set the delays for each of the elements Note that this option makes the three parameters that usu ally describe the dynamic focusing Number of focal zones Start depth of first focal zone and End depth of last focal zone as well as the parameters used in the focusing algorithm Speed of Sound Transducer diameter and Radius of Curvature redundant and these will be removed from the submenu The following option will become available when the electronic time delays are set manually If focus mode is set to 2 way there will be 2 new options one for transmit and one for receive 22 Time delays transmit rstartfimm rstop mm delay el 1 5 ns 12 21 00000 21 45 00000 T he number of rows in the above matrix for electronic time delays equals the number of focal zones desired The number of focal zones and thus the number of rows in the above matrix is optional The two leftmost columns hold the values of the start and stop depths of each focal zone while the remaining columns show the time delays on transducer elements I column 3 to 5 column 7 In this example the annular transducer is divided into 5 rings Note that transducer element 1 refers to the inner ring of the annular transducer The electronic time delay matrix is entered analogously to the constant delays vector see above You have to enter one row at a time as a vector containing the start and stop values an
44. ge 78 mm 2 2 Example 2 On axis field Load e2 bpax cnf and compute by Calculations Beam Pattern Peak Calculation to get the beam pattern for an annular array on the axis for range to 100 mm 2 3 Example 3 2D response pulsed grating lobes Load e3 2dgr cnf and compute by Calculation 2D response Com pute response Visualize the result by the command Calculation 2D response Surface plot using default values for the parameters The result is pulsed grating lobes for a linear array with a pitch of 2 lambda The re sult may also be visualized using the Contour plot or the Color encoded commands in the same menu 2 4 Example 4 2D response continuous wave Load e4 2dew cnf and compute by Calculation 2D response Com pute response Visualize the result by the command Calculation 2D response Surface plot using default values for the parameters This is the continuous wave field from a phased array with pitch lambda 2 The field may also be visualized using the Calculation 2D response Contour plot command Instead of using default values you should reflect the plot about the z axis If the iso option is used one gets a contour plot of the beamwidth showing clearly the effect of focusing April 8 1998 13 ver 2 1 ULTRASIM USER S MANUAL 2 5 Example 5 2D response moving pulse Load e5 2dmov cnf and compute by Calculation 2D response Com pute response Visualize the result by t
45. he command Calculation 2D response Surface movie using default values for the parameters The re sult is 11 simulations of a pulse travelling in depth containing pulsed grating lobes 2 6 Benchmark calculation The file benchmrk cnf contains a simulation intended for measuring the relative performance of the computer It is small enough to run on a Pen tium PC with 8 Mbytes of RAM without paging thus only CPU power is measured Typical performance is e SUN Sparc 2 71 sec e DEC 5000 240 37 5 sec e Pentium 90 MHz Windows 95 32 5 sec e IBM RS6000 11 sec e DEC alpha 9 8 sec These execution times are computed using the m file version of the Cal culation 2D response Compute response command There is also a C version Mex file that will improve performance by a factor of 3 4 The result can be visualized using the Calculation 2D response Sur face plot using default values for parameters April 8 1998 14 ver 2 1 ULTRASIM USER S MANUAL 3 SIMULATION OF ACOUSTIC FIELDS 3 1 Introduction In medical ultrasound a whole range of various transducers are common including 1 Pre focused annular arrays divided into rings using the equal area prin ciple 2 Rectangular arrays divided into elements of dimension 0 5 2 A with pre focusing in the short axis dimension 3 Curved arrays divided into elements of dimension 1 2 with pre focusing in the short axis dimension In addition there is need to
46. he current plot The Zoom In command lets you choose the part you want to blow up by designating the lower left and upper right corner Zoom Out restores the original April 8 1998 54 ver 2 1 ULTRASIM USER S MANUAL plot using Matlab s auto scaling of the axis which implies that the axes extremities are set according to the maximum and minimum values of the data to be plotted 7 3 Options The Options menu allows you to toggle the state of the flags Hold and Grid e Hold On Off turns hold on or off depending on the present state When hold is on the next plot which is plotted in the window will be added to the current plot s If hold is off the next plot will replace the current one e Grid On Off turns the overlay grid on or off depending on the present state 7 4 Text The Text menu contains several items which control the properties of the text written in the graphic window The options available should be self explanatory but some comments on how to use them follow here Before using any of the Font Style Size Alter Text and Delete options a text object must be chosen This is done by placing the arrow at the text object with the mouse and clicking the left mouse button box should now appear around the text object to indicate that it is selected Note that in some cases changing the Font Style or Size property of a text object may not become visible on the screen but the selected property should
47. he outer ring has the maximum element no N April 8 1998 26 ver 2 1 ULTRASIM USER S MANUAL 4 5 Beamforming Parameters The Beamforming submenus control the electronic focusing and the apodiza tion weighting of the transducer There are two different menus depending on the value of the Focus Mode flag one for fixed focus and one for dynamic focus 4 5 1 Fixed Focus As stated in subsection 4 1 Focus Mode flag should be set to Fixed Focus with the exception of the case which is commented on in the next subsection Dynamic Focus The Beamforming submenu for the case of fixed focus looks like this when the TransducerGeometry flag is set to Rectangular and Curved Array BEAMFORMING SUBMENU Fixed focusing transmit mode 2 Electronic focusing x mm 0 3 Electronic focusing y mm 0 4 Electronic focusing z mm 100 5 Apodization Azimuth no apodization 6 Apodization Elevation no apodization Parameters used in focusing algorithm 14 Speed of Sound c m s 1540 Note that when the TransducerGeometry flag is set to Annular Ar ray focusing off axis is impossible and the three options Electronic focusing t y z will be replaced by the single option 4 Electronic focusing depth mm 100 Electronic focusing depth gives you the possibility of specifiying a depth to which the transducer will focus by setting time delays on the rings of an annular transducer By setting this depth eq
48. iefly as using these functions is the best way of getting acquainted with them 5 1 Excitation transmitted signal This option plots the transmitted signal and its frequency spectrum The upper graph shows the time domain signal the amplitudes of which are nor malized The lower graph shows the frequency spectrum plotted for frequency ranging from zero to 4 times the center frequency of the signal Note that there will be no graphical output when a CW signal is transmitted 5 2 Spectrum with depth This option gives the transmitted spectrum and the spectrum at certain depths in the medium using the Medium parameters for frequency depen dent attenuation 5 3 Observation The Observation option displays the observation point line or plane chosen in the Configuration menu Four plots are displayed one 3D plot and three 2D plots for the xy xz and yz planes respectively Note that the proportions of the plots may be somewhat misleading due to Matlab s autoscaling of the axes 5 4 Media 5 5 Transducer There are two ways to view the Transducer 2D plots and Surface 2D plots plots the points used to represent the transducer in two different projections There is one plot for the xy plane and another for the xz plane The second option Surface makes a plot of the transducer based on the collection of points representing the transducer The plot of the transducer can be rotated and tilted and the shading and color can be
49. ility of verifying your configuration graphically by selecting one of the options in the View menu This is looked into in section 5 The remaining options refer to the graphic display of the Configuration window Print produces a hardcopy or a Postcript file of the graphic contents of the window Note that selecting an item in the View menu will produce a graphical output in the Configuration window cf section 5 while running a simulation produces a graphical output in the Plottool window cf sections 6 amp 7 Clear clears the graphic display while Subplot allows you to split the screen into several parts subplots before plotting Colormap and Shading applies to the cases where a 3D surface is plotted in the window April 8 1998 10 ver 2 1 ULTRASIM USER S MANUAL Colormap lets you change the color of the surface while shading lets you choose between three different shading styles on the surface 1 6 How to set the coordinates Transducer Figure 2 Coordinate system of UltraSim In UltraSim you have a choice between using Carthesian and spherical coordinates Figure 2 demonstrates how both the Carthesian x y z and the spherical r 0 4 coordinates at the point marked with an asterisk are defined As can be seen from the figure the origin of UltraSim s coordinate system is placed at the center of the transducer so that the beam center of the emitted ultrasound wave coincides with the z axis There are two e
50. increasing elements beyond 1000 will have no effect as UltraSim will convert pvector to a vector holding 1000 elements in any case e The pulse amplitudes may also be chosen arbitrarily since the am plitudes will be normalized at a later stage i e only the amplitude relative to the maximum amplitude is considered When pvector is defined choose the Excitation submenu and select option 13 Pulse Type Then choose User Defined from the menu which is dis played When quitting the Excitation submenu pvector will be converted to a standard UltraSim format and stored in the variable pvec which will be used as excitation signal when running an Energy simulation cf sub section 6 1 Note that if User Defined is chosen as pulse type and pvector is not defined a warning will be displayed and Pulse Type will be set to its default Ultrasim There is also a third Pulse Type option User Defined Individual pulses for each element which allows you to define the emitted pulse from each of the elements of a transducer To use this option N vectors pvectorl pvector2 pvectorN N is elements on the transducer have to be defined The vectors must be on the same format as pvector above and the pulse emitted from transducer element no n 1 lt n lt N must be defined by pvectorn This option will normally be useful with transducers with a small number of elements such as annular transducers where the inner ring is element no 1 and t
51. ive some introductory remarks here If this is the first time Ultrasim is started for this user a system startup file will be read from directory given in ULTRASIMHOME variable Each time one exits Ultrasim using the File Quit Ultrasim or File Quit Mat lab commands the present setup is saved in the user s startup cnf file in directory given in USER ULTRASIMHOME variable This file is then automatically loaded when Ultrasim is again started To set up a configuration and perform a simulation start with the menu items to the left on the menu bar and progress towards the right If you already have saved a configuration for a simulation choose the option Load Configuration in the File menu Files are saved with name cnf old format had file name cnf mat There are example setups available under the read only directories for various kinds of transducers and simulations If you want to change the setup you have to go through all the submenus of SetFlags to set the basic properties of the configuration as described in subsection 4 1 Then you should set the configuration parameters in the Configuration submenus as described in subsections 4 2 4 3 If you are particularly satisfied with the set up and want to save it for later use you may do so by selecting Save Configuration in the File menu When the configuration is set you are ready to start a simulation from the Calculations menu as described in section 6 You also have the possib
52. lation is stored in the following vectors flagg flags for setting top level simulation parameters e option information about current observation space e transducer parameters describing the transducer e excitation parameters describing the excitation and the beamforming e medium parameters describing the acoustic medium e observasjon parameters describing the observation space Other variables are derived from the setup parameters and always kept in the workspace The main ones are e elem pts variable containing coordinates and azimuth and elevation element numbers for each point on the transducer surface e centers variable containing coordinates and azimuth and elevation element numbers for each element of the transducer e r y 2 t variables containing coordinates and time for each point in the observation space Finally the variable comment should be mentioned It contains a free format sentence describing the contents of the setup that was just read from file C 2 Flagg amp option e flagg 1 11110 e option x x x April 8 1998 65 ver 2 1 ULTRASIM USER S MANUAL C 2 1 Flagg Var name Description flagg 1 focus mode flagg 1 Fixed focus 2 Dynamic focus steered response flags 2 geometry flagg 1 YA and 2D ret tampas array 2 N 3 ae array flagg 3 medium flagg I homogeneous 2 layered 2D 3 layered 3D flagg 4 coordinates fl 1 oo 254 20 2 N 3 VAA range e
53. levation azimuth r 6 t 4 spherical r sind sind t flagg 5 pitch mm 1 mm input in mm 2 pitch input referred to lambda flagg 6 attenuationflag 0 no attenuation 3D medium only 1 absorption included 2 reflection losses included 3 absorption and reflection losses included NOTE that flagg 4 and flagg 5 only tell how to input parameters while flagg 1 flagg 2 and flagg 3 gives information on how to interpret param eter vectors The definition of the beampattern is that the source is moved and the delays are fixed while the steered response is obtained by changing the elec tronic steering and focus and keep the source at a fixed position See defini tions in 5 C 2 2 Option option is a vector that contains information about what type the current observation space is The first letter option 1 is the dimension of the observation space and may be p 1 2 3 m or f for a point a 1 dimensional line a 2 dimensional plane a 3 dimensional volume 3 dimensional variation 2 d plane time or 4 dimensional variation 3 d volume time The second and third letters give the axes with variation Examples are given in the table Syntax option 3 letters April 8 1998 66 ver 2 1 ULTRASIM USER S MANUAL IF option is THEN observation space Is p a POINT 15 a LINE where y z and t are fixed ie variation parallel to x axis a LINE with variation along r axis 1s
54. m features e Annular Phased Linear or Curved array transducers in 1 1 5 and 2 dimensions e Free choice of transducer parameters aperture Radius of curvature elements e Free choice of frequency e Pulsed or Continuous wave excitation Facilities for Electronic focusing Quantization of electronic time delays Apodization e Homogeneous or layered media with smooth surfaces Acoustic Wave Field Simulations at a point along a line in a plane e Annular array design tool UltraSim also offers possibilities of simulations including losses in media and reflection losses at surfaces between media of different wave velocities April 8 1998 7 ver 2 1 ULTRASIM USER S MANUAL 1 2 About Matlab Matlab is a computer programming language supplied by the Mathworks Inc which is particularly advantageous for use with numerical calculations and also provides powerful routines for handling graphics The language is object oriented and is mainly based on C and Fortran Some knowledge of Matlab will be advantageous when using UltraSim but it is not required 1 3 About this document T he present document is written as an introductory document and reference book to UltraSim UltraSim s menu system should be self explanatory to a large extent and reading the entire document should not be necessary However if this is your first acquaintance with UltraSim you are adviced to read the rest of the Introduction sectio
55. n and then load the examples described in the tutorial Then read the section on Simulation of Acoustic Fields and use the subsequent sections as a guideline when making the configuration for your first simulation Instructions for installation and for programming UltraSim may be found in the Appendices A link to the latest electronic version of this document may be found on http www ifi uio no sverre 1 4 History The program started as a Matlab toolbox called ARRAY It was developed at Vingmed Sound for simulation of array systems in 1990 91 and was designed by Sverre Holm and Trond Kleveland who both have been following the project since then Other contributors have been e Tor Arne Reinen SINTEF DELAB 1992 Start of 2D array module e Lars Odegaard Dr Ing student IFBT IMF 1992 1996 Wave prop agation in layered media 13 e Vebj rn Berre IFBT scientist 1992 1993 Renamed program to UL TRASIM made it compatible with MATLAB 4 0 and designed menu system and new data structures e Kari Lervik Siv Ing IFBT 1992 Start of 1 5D module e Espen Iveland Siv Ing IFBT 1993 Annular array optimization April 8 1998 8 ver 2 1 ULTRASIM USER S MANUAL e Frode Teigen IFBT scientist 1993 1994 Completed 1 5D upgraded beam pattern module to energy summation and input of measured pulse worked with Lars degaard on layered module plus did general upgrading e Jan Ove Erstad Cand Scien
56. n points field points coordinates of the observation points field points time coordinates of the observation points field points April 8 1998 72 ver 2 1 ULTRASIM USER S MANUAL C 7 Dependent parameters lambda c f m 1 2 e 1 Wavelength FN focal dist aperture function of e 2 4 t 1 f stop C 8 Administration parameters Loaded_ file Contains the currently loaded configuration file name Saved file Contains the name of the configuration file saved most recently plotfig Handle of PLOTTOOL figure config Handle of ULTRASIM CONFIGURATION CALCULATION figure comment comment line for data saved to file C 9 Temporary variables convention If you can t make up your own names for temporary variables you can use these temp tmp Temporal variables eg temp input tempobj Temporal variable for objects eg tempobj10 uimenu ind Temporal variable for indexes eg ind find Y 0 com coml holds COMmand that is to be executed in submenu count counter variable in loops April 8 1998 73 ver 2 1
57. nce from the transducer to the plane where you are observing which normally is approximately equal to April 8 1998 33 ver 2 1 ULTRASIM USER S MANUAL t 3 f NA VA z Li o t proparZ C Figure 7 Calculation of propagation and pulse times the fixed z value Then you can calculate the time at which the pulse from the transducer arrives to the plane propagation time tpropag distance Speed of Sound t z c Speed of sound is set in the Medium submenu Note that the pulse will be emitted at time O tpuise 2 1 e at time t 0 half of the pulse is already emitted The pulse time is calculated as tpulse periods f cf fig 7 where periods is 3 This is illustrated in fig 7 Thus the time chosen should be in the approximate region t tpropag tpuise 2 tpropag tpulse 2 as there will be no signal outside this region Within these limits you may choose a time depending on which part of the signal you want to observe Observation in the xz or yz plane When observing in the xz or yz plane it is convenient to choose the time so that all of the pulse or a maximum of the pulse is within the observation plane at the actual time See the above paragraph for details on how the time should be calculated Observation in the xt plane When observing in the xt plane it is nat ural to choose a time so that approximately all of the pulse passes the line defined by the x values and the fixed z and y values
58. ng with the medium s velocity of sound For rectangular arrays the focus flag can be set to Dynamic Focus In this case the aperture and focus will vary with depth and be updated as often as specified by the number of observation points per mm The aperture grows with depth according to a fixed f stop until the azimuth aperture specified for the transducer is reached 6 2 2 Compute Response The simulation is started by clicking on Compute Response The complex result is found in the vector array_resp The result may be displayed in several different ways 6 2 3 Surface This option is used for displays of temporal evolution movie option and for showing the logarithmic or linear plot of energy as a function of space or space time see Fig 4 Both the rf signal and the envelope may be shown April 8 1998 46 ver 2 1 ULTRASIM USER S MANUAL 6 2 4 Contour plots This option is used for finding the contour plot of energy The plot may be mirrored over the first axis for symmetric fields This will save 50 of the computations Contour levels may be set in either the logarithmic or the linear domains When the iso contour option is used the energy dis tribution is normalized so that the maximum is 1 Therefore this option is used for finding beamwidths The elevation beamwidth fixed lens in rectan gular arrays may be found by simulating the y z plane and the azimuth beamwidth by using the x z plane see Fi
59. on Under the above contitions Integrate Sidelobe Energy will produce a plot where the total energy which lies outside a given angle phi is plotted for all phi from 0 to 90 degrees Thus the value at phi a is the energy integrated from a to 90 divided by the total energy April 8 1998 45 ver 2 1 ULTRASIM USER S MANUAL 6 2 2D Response The 2D response function simulates the field in a 2D plane The plane may be either in space or in space time Travelling pulses may be simulated by using the movie option in a plane or a volume Only Cartesian coordinates can be used for the observation plane or volume The program works according to the same principle as the beam pattern option i e by using a discrete version of the Rayleigh integral and summing from points in the source to points in the observation plane 6 2 1 Observation Plane The coordinate flag must be set to rectangular and the observation flag to either plane or plane gt movie The observation plane can be set up in the x z y z or x y plane for finding the spatial distribution at a fixed point in time Alternatively the plane can be set up in the x t y t or z t plane for finding the temporal distribution along a line When the movie option is used the observation plane is x z t y z t or x y t Number of observation points per mm determines the sampling grid in the spatial dimension and also in the temporal dimension by scali
60. on which is obligatory when using a Layered 2D medium is restricted to on axis simulations using an annular transducer since this simulation method exploits rotational symmetry See also subsection 4 6 for more details 4 1 4 Coordinates and pitch mm The Coordinates and pitch mm flags lets you choose the format of the parameters in the submenus of Configuration cf subsections 4 4 4 3 You may use either rectangular or spherical coordinates For spherical co ordinates the angles may either be specified directly or by their sines The last option is for display in the wavenumber domain and gives possibilities for setting sines that are larger than 1 in magnitude i e imaginary angles pitch mm may be set to either mm implying that all distances are given in mm or pitch when all distances are given in units of wavelengths Note that when observing along a line transversal to the transducer normal setting the Coordinates flag to rectangular gives a straight line while choosing spher ical coordinates gives a curved line where each point on the line are equally distant from the center of the transducer cf subsection 4 7 April 8 1998 20 ver 2 1 ULTRASIM USER S MANUAL 4 1 5 Observation The selection of the observation flag is strongly related with the type of sim ulation you want to use Observation at a point is only compatible with the 2D layered medium simulation If you are planning to use this simulation method
61. onic time delays cf subsection 4 5 are quantized with a quantizing time step of 1 fsampte If Quantizing of Time Delays is Off Default the electronic time delays are not quantized and thus the sampling frequency is not used Therefore the sampling frequency is not displayed in the excitation submenu when Quantizing of Time Delays is Off However it is included in the above menu for convenience Pulse Type should be set to its default Ultrasim except when you want to use a pulse which may not be presicly defined by the above Frequency Transmitted pulse length and Pulse Weighting parameters Normally this exception occurs when you want to use a pulse which has been measured experimentally Also note that setting Pulse Type to any other value than the default will work only if you plan to run an Energy simulation which is found in the Beampattern submenu cf subsection 6 1 Below the somewhat tricky operation of using a User Defined pulse is described 4 4 1 Pulse Type Advanced The Pulse Type option allows you to choose between the pulse defined in the above menu i e The pulse is defined by the parameters set in options 1 9 and 10 and a User Defined pulse usually an experimentally measured pulse Pulse Type Ultrasim designates a pulse as defined in the excitation submenu while a User Defined pulse must be defined by the user in a global vector pvector User Defined pulse overrides the values of the Frequency Tran
62. pretation of the medium variable depends on the MEDIUM FLAG flagg 3 1 homogeneous 2 layered 2D 3 layered 3D In all tables in this section the variable names are shortened so that m 1 2 is equivalent to media 1 2 April 8 1998 70 ver 2 1 ULTRASIM USER S MANUAL C 5 1 HOMOGENEOUS SYNTAX media c jer Bee c m 1 2 Velocity of sound in layer 1 Zn m 1 8 Characteristic impedance of layer 1 alpha m 1 9 Attenuation parameter 1 in layer 1 beta m 1 10 Attenuation parameter 2 in layer 1 The attenuation parameters are defined by I 19e 97 where r em f MHz 8 dimensionless a m MHz e g a 6 9 and 8 1 0 gives 0 3 dB cm MHz derating C 5 2 LAYERED Please refer to Advanced User s Manual for documentation C 6 Observation points sources Z phi azimuth p theta elevation h phi i Rectangular x y z Spherical r theta phi y theta Su Sgail N NI Figure 15 Definitions used for spherical coordinates azimuth and elevation The coordinate system is determined by flagg 4 1 rectangular x y z t April 8 1998 71 ver 2 1 ULTRASIM USER S MANUAL 2 spherical r 0 t 3 spherical r sind sino t Syntax OBSERVASJON start x start y start z start t end x end y end z end t resolution thirdpoint x thirdpoint y thirdpoint z thirdpoint t coordinatesystem Variables define
63. s may have different amplitudes due to an apodization which may also be set in the Beamforming submenu A pulse from a transducer point arrives at an observation point at time tobservation ttransmit r c where r is the distance between the transducer point and the observation point and c is the sound velocity At the observa tion points the pulses from each transducer point are added as they arrive in order to get the pulse form at each observation point as shown in an example in fig 9 Note that the time delays are all At 0 and t 0 Tnear is the distance to the point on the transducer closest to the observation point while ffar is the distance to the point on the transducer farthest away from the observation point pat fa IC ty za IC touse 2 o Figure 9 Example of total pulse at the observation point The resulting pulses at all observation points may be represented in either a plot of the Energy vs observation point coordinates or in a plot of Peak amplitude vs observation point coordinates These methodes are described below ENERGY In fig 10 the pulses received at all observation points are merged in order to get a 3D plot of the pulsed wave around the line of observation Fach line along the radial direction which also can be thought of as the time axis represent the pulse sampled at one of the observation points while lines along the transversal direction represent a sample of the pulses at all ob
64. s wave CW The following parameters are only used for annular arrays in the layers module e 15 Transducer diameter used in delay calculations e 16 Transducer ROC used in delay calculations e 17 Focus mode e 18 Delay calculation method e 19 of focal zones receive e 20 start focal zones receive e 21 end focal zones receive April 8 1998 69 ver 2 1 ULTRASIM USER S MANUAL C 4 2 Excitation beamforming The interpretation of the excitation variable depends on the focus mode flag which is flagg 1 1 Fixed focus 2 Dynamic focus steered response Apodization amp phase noise This interpretation is independent of any flag apod numb el apod numb az e 6 Number which selects the apodization type e 5 Number which selects the apodization type none 0 Hamming 1 Hanning 2 Kaiser Bessel 3 e 7 Phase Noise component for steering delays TYPE e 8 Phase Noise component for steering delays parameter Fixed focus ie flagg 1 1 r e 2 Electronic focusing range 0 e 3 Electronic focusing elevation angle e 4 Electronic focusing azimuth angle Note that r may be infinite for focusing in the far field Dynamic focus ie flagg 1 2 N_ zones e 2 number of focal zones continous N zones Inf start depth for dynamic focusing stop depth for dynamic focusing C 5 Medium The inter
65. servation points at a given time The pulse is sampled with a sampling frequency fs 4x fo where fo is the center frequency of the signal To get a representation of the pulse energy at an observation point all samples of the pulse at the observation point are squared and added together Energy y 3 n April 8 1998 42 ver 2 1 ULTRASIM USER S MANUAL SSS 3 KR N S SS gt RISE RAK Ss ONENESS IQ ALIAS SJ SKK NA IN NRS SOS SAN NR NE SASS SORA SSS SS Figure 10 3D plot of Beampattern pulse samples where s is pulse sample number n at the observation point The energy is normalized so that the energy in the focal point is 0 dB when no attenuation is present n example of the resulting beampattern energy curve which is displayed in the plottool window is given in fig 11 Beampattern Energy a energy dB R 254 304 35 Transversal distance Figure 11 Example of energy diagram PEAK The second option in the Beampattern submenu Peak uses the en velope of the wave when plotting the results The envelope of the pulses presented in the 3D plot of fig 10 is shown in fig 12 Note that all the data necessary to obtain the plot of fig 11 are not calculated when using the Peak April 8 1998 43 ver 2 1 ULTRASIM USER S MANUAL E fil 3 m Eos fi i il q E 100
66. smitted pulse length and Pulse Weighing parameters and as a conse quence the Transmitted pulse length and Pulse Weighing parameters are not displayed in the Excitation submenu if a User Defined pulse is to be used However the Frequency still has to be set to a value approximately equal to the frequency of the user defined pulse as this frequency will be used when calculating an appropriate sampling frequency not to be confused with the Sampling frequency in the Excitation submenu for sampling the observed signal see subsection 6 1 for details Note that the use of a User Defined pulse will require some knowledge of Matlab April 8 1998 25 ver 2 1 ULTRASIM USER S MANUAL pvector must be defined before selecting the Excitation submenu and is to be on the following format e Define the vector as global Write global pvector e Element 1 of the vector i e pvector 1 is the time steps between each of the following elements Thus pvector 1 elements 2 will be the duration of the pulse described by pvector e The remaining elements of pvector are the amplitudes at time pvector 1 elementno 2 Thus pvector 2 is the amplitude at t 0 pvector 3 is the amplitude at t pvector 1 and so on The negative sign accounts for the fact that the start of the pulse is defined to be at t 0 e The length of pvector elements may be chosen arbitrarily Increas ing elements will increase the resolution but
67. t IFI 1993 1994 Coarray module and Remez optimization module for thinned arrays 10 e Bj rnar Elgetun Cand Scient IFI 1994 1996 Completed movie module improved user interface made optimization programs for thinned 2D arrays 12 e Einar Halvorsen IFBT scientist 1995 1996 Worked with Lars de gaard on layered module e Kapila Epasinghe Cand Scient IFI 1995 Made volume and slice simulations and C and parallel computer versions of 2D response com putation 14 1 5 Getting started 7 ULTRASIM CONFIGURATION CALCULATION File SetFlags Configuration View Print Clear Subplot Calculations Colormap Shading Figure 1 The UltraSim Configuration window April 8 1998 9 ver 2 1 ULTRASIM USER S MANUAL To start UltraSim from a UNIX system you first have to start Matlab with the command matlab in an xterm window Then UltraSim may be started with the command usim which makes two graphic windows with a menu bar each pop up The xterm window where you start UltraSim will later be referred to as the text window The Plottool window where the results are plotted will be described in section 7 Figure I shows the Configuration window where the configuration needed to perform a simulation and the method of simulation are selected The important items on the menubar on top of the UltraSim Configuration window will be described in detail in sections 4 6 However it will be adequate to g
68. ter end value 20 of totally 11 plots of totally 11 plots of totally 11 plots of totally 11 plots of totally 11 plots of totally 11 plots of totally 11 plots of totally 11 plots of totally 11 plots of totally 11 plots of totally 11 plots plot number plot number plot number plot number plot number plot number plot number plot number O ON DOB QN plot number ER o plot number plot number Movie Options gt Enter number of movie loops 1 100 gt Enter speed in frames sec 1 20 Movie is playing gt More movie 77 y n n April 8 1998 50 ver 2 1 ULTRASIM USER S MANUAL 6 4 Coarray Tools In this menu the user can find the difference and the sum coarrays plot the coarray together with an error coarray if it has been calculated and do some optional plotting like e g finding the beam pattern from the coarray 10 User operation is done by striking a key while pointing at the UltraSim plot tool window April 8 1998 51 ver 2 1 ULTRASIM USER S MANUAL April 8 1998 52 ver 2 1 ULTRASIM USER S MANUAL 7 PLOTTOOL All results from simulations are plotted in the Plot window which is shown in figure 14 The menubar on top of the Plot window includes features for saving results and manipulating the graphic display Below the most impor tant items on the menubar are explained while the remaining items Print Clear Subplot Colormap and Shading are
69. the line is parallel the remaining coordinates will have a fixed value for every point on the line It can easily be seen that if you are using spherical coordinates the line will be an arc if the selected axis is theta or phi When the observation option is a plane UltraSim will ask you to select two axes to which the chosen plane will be parallel You are also allowed to select t time as one axis see the below subsection for details Note that tis not used when observing along a line or at a point Obviously all the values will be fixed if the observation option is a point Start value and End value of y or x z give the extremeties of the line Thus the line will be represented by pixels along axis points equally separated between the Start value and the End value of the Selected azis while the other coordinates x and z in this example will be fixed The plane will be represented in a similar manner only that the resolution is defined in an alternative way see above Fixed value of xyzt r phi theta if spherical coordinates are chosen de termines a fixed value for the coordinates which are not a selected axis see above Note that t time is only used when observing in a plane and that when point is the observation option all the values are fixed 4 7 1 How to set time when observing in a plane Observation in the xy plane To set the time when observing in the xy plane you first will have to find the average dista
70. ual to the transducer s radius of curvature cf subsection 4 3 you will turn off the electronic focusing i e the electronic time delays are zero on each element Electroning focusing x y z allows you to specify a point rather than just a depth to which the transducer will focus x y and z are the coordinates of the point Note that when the Coordinates flag is set to Spherical the xyz coordinates will be replaced by r phi and theta April 8 1998 27 ver 2 1 ULTRASIM USER S MANUAL Apodization Azimuth Elevation lets you choose between the following apodization weighting functions in the azimuth and elevation directions No Apodization Hamming Hanning Kaiser Bessel User Defined To get an idea of the nature of the above apodizing functions select an apodizing function in the Beamforming submenu and look at the resulting weighting by choosing Apodization in the View menu cf subsection 5 6 Note that when the Transducer Geometry flag is set to Annular Array the 2 options Apodization azimuth elevation are replaced by a single option for choosing apodization Also the Kaiser Bessel Apodization will not work for annular transducers Speed of Sound refers to the value used in the focusing algorithm which calculates the electronic time delays for focusing to a point 8 This value for the speed of sound should not be confused with the value set in the Medium submenu which is the actual sound velo
71. ulation and can be used to optimize weights for sparse perturbed and non equally spaced array as well as equi spaced array 10 The current version is user interrupt able in every iteration The x key should be pushed when asked to strike a key This has been useful with arrays that converge slowly because a more dense sampling then might help The sampling density is determined by the Grid spacing variable which has 16 as the default value It has been observed that in some cases a less dense sampling is more efficient The input format is l s do K Here do is the cut angle for the mainlobe in degrees 6 is the angle where one wants the equiripple sidelobe level to be reached db is the upper limit for the optimization region and K is the approximation error weight value in most cases 10 The brackets must also be entered 4 9 List The last item in the Configuration menu List lists all the parameters set in the submenus treated above You may choose to list the parameters to the screen or to a text file April 8 1998 35 ver 2 1 ULTRASIM USER S MANUAL April 8 1998 36 ver 2 1 ULTRASIM USER S MANUAL 5 VIEW The View menu is useful for verifying that your choice of parameters in the Configuration menu is sensible If you are new to UltraSim you are adviced to verify changes to the configuration by selecting the appropriate item in the View menu Below all the menu items are described br
72. xceptions to the last statement First the beam from a linear array may be steared off the z axis This will not change the position of the transducer Secondly the annular transducer may be tilted relative to the z axis if you are planning on using simulation option Layers and comments to Rotation angle in subsection 4 3 1 Note that when using the simulation option Layers only two dimensions are used and that the coordinate system coincides with the xz plane of fig 2 Note also that the z axis is the abscissa and the x axis the ordinate of this 2D coordinate system A standard rectangular transducer has its elements distributed along the x axis Standard azimuth beamprofiles are obtained by setting 0 0 and vary Data fixed value of r April 8 1998 11 ver 2 1 ULTRASIM USER S MANUAL April 8 1998 12 ver 2 1 ULTRASIM USER S MANUAL 2 TUTORIAL Go through these examples first to familiarize yurself with the basic features of Ultrasim Each example is loaded by entering File Load 2 Ultrasim examples The transducer geometry can be viewed by View Transducer 2D plots and the parameters can be inspected by going through all the submenus in the Configuration menu 2 1 Example 1 Beam pattern in focus Load el bpfoc cnf and compute by Calculations Beam Pattern Peak Calculation or Calculations Beam Pattern Energy Calculation to get the beam pattern for an annular array from 50 to 50 degrees in focus ran

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