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User Manual for the DREAM Toolbox Version 2.1.3 An ultrasound

1. db cm MHz is shown in Figure 6 for 10 mm 25 mm and 40 mm respectively Casual Greens Functions for Lossy Media a 1 dB cm MHz Attenuation coefficient 1 dB cm MHz 0 T T T T z 10 mm 2 10 mm 2 25 mm Dn z 25 mm Z 40 mm Ap 1 2 40 mm 06 4 Sots ok Me Rs s oo a 3b s lt s s 4 N z t Me wg E al 3 x J a N 5 k s 6 N sa J s s i 7 X a gt ing en A 4 5 84 ES 4 A l Sy el a N 10 fi i i f a 0 5 10 15 20 25 30 35 40 0 0 5 1 15 25 3 Time us Frequency MHz a Time domain response b Frequency domain response Figure 6 Illustration of the attenuation response at three different depths The attenuation coefficient a was 1 db cm MHz and the attenuation response at 10 mm is the solid line 25 mm is the dashed line and 40 mm is dash dotted line respectively 6 A Quick Start to DREAM Simulations N his section a quick start on how to perform simulations with DREAM is presented Here only a simple example is shown just to illustrate what is needed to simulate an ultrasonic measurement system We will use a circular transducers for this example but more advanced examples can be found on the DREAM web page http www signal uu se Toolbox dream on the Examples page Also more details of the various functions in the DREAM Toolbox can be found in Sections 7 8 and 10 respectively Let us study a the pressure respo
2. The on axis SIR has duration t tz with the constant amplitude cp in the time interval tz lt t lt t 1A DREAM 5 AN INTRODUCTION TO THE IMPULSE RESPONSE METHOD 1800 7 7 7 T 7 1800 1600F J 1600F 7 1400F 4 1400F 7 cy a 1200 J 1200 3 3 3 1000F 13 1000F J J 800 1 g 2 800 lt x lt x oc 600 7 cc 600 J an 19 400 400 200F J 200F 7 0 i i i i 0 i i i i 0 5 10 15 20 25 30 40 45 50 55 60 65 70 t us t us a Spatial impulse response at z 20 mm b Spatial impulse response at z 80 mm Figure 3 On axis spatial impulse responses for a 10 mm disc where the sound speed cp was 1500 m s 5 2 Discrete time Spatial Impulse Responses Before we introduce the discrete representation DR method which the DREAM toolbox transducer functions are based on let us discuss sampling of spatial impulse responses This is of interest since our ultimate goal normally is to model the total sampled imaging system which includes both acoustic propagation effects the SIRs as well as input signals and electro acoustical effects To obtain a discrete model we need a discrete representation of the SIRs That is the analytical expressions for the SIRs discussed in Section 5 1 must be converted to a discrete form in order to be useful for digital signal processing a proper discrete representation of the SIRs is necessary so that when the sampled SIR is convolved with the normal velocity the
3. Transducer type operation DREAM function Linux Mac Windows Strip transducer dreamline_p Yes Yes Yes see Sec 4 2 Rectangular transducer dreamrect_p Yes Yes Yes see Sec 4 2 Focused rectangular transducer dreamrect f p Yes Yes Yes see Sec 4 2 Circular transducer dreamcirc_p Yes Yes Yes see Sec 4 2 Focused circular transducer dreamcirc_f_p Yes Yes Yes see Sec 4 2 Spherical concave transducer dreamsphere_f_p Yes Yes Yes see Sec 4 2 Spherical convex transducer dreamsphere_d_p Yes Yes Yes see Sec 4 2 Cylindrical concave transducer dreamcylind_f_p Yes Yes Yes see Sec 4 2 Cylindrical convex transducer dreamcylind_d_p Yes Yes Yes see Sec 4 2 Array with rectangular elements dream_arr_rect_p Yes Yes Yes see Sec 4 2 Array with circular elements dream _arr_circ p Yes Yes Yes see Sec 4 2 Array with cylindrical concave el dream_arr_cylind_f_p Yes Yes Yes see Sec 4 2 Array with cylindrical convex el dream_arr_cylind_dp Yes Yes Yes see Sec 4 2 Annular array dream_arr_annu_p Yes Yes Yes see Sec 4 2 Time domain convolution conv_p Yes Yes Yes see Sec 4 2 Frequency domain convolution fftconv_p Yes Yes Yes see Sec 4 2 Frequency domain convolution sum_fftconv_p Yes Yes Yes see Sec 4 2 Parallel copy of data copy_p Yes Yes Yes see Sec 4 2 Synthetic aperture focusing technique saft_p Yes Yes Yes see Sec 4 2 Table 2 Functions in the DREAM Toolbox with parallel thre
4. J Acoust Soc America 49 1629 38 1971 K Aki and P Richards Quantitative Seismology W H Freeman San Francisco 1980 J Lockwood and J Willette High speed method for computing the exact solution for the pressure variations in the nearfield of a baffled piston J Acoust Soc America 53 735 741 1973 http www fftw org V A Del Grosso New equation for the speed of sound in natural waters with comparisons to other equations J Acoust Soc America 56 1084 109 1974 P Stepanishen Pulsed transmit receive response of ultrasonic piezoelectric transducers J Acoust Soc America 69 1815 1827 1981 C Wiley Synthetic aperture radars IEEE Trans on Aerosp Electron Syst 21 440 443 1985 C Sherwin J Ruina and R Rawcliffe Some early developments in synthetic aperture radar systems IRE Trans Military Electron 6 111 115 1962 P Gough and D Hawkins Imaging algorithms for strip map synthetic aperture sonar Minimizing the effects of aperure errors and aperture undersampling IEEE Journal of Oceanic Engineering 22 27 39 1997 J Seydel Ultrasonic synthetic aperture focusing techniques in NDT Research Techniques for Nondestructive Testing Academic Press 1982 S Doctor T Hall and L Reid SAFT 4he evolution of a signal processing technology for ultrasonic testing NDT International 19 163 172 1986 C Frazier and J W D O
5. 7 3 6 Spherical Concave Transducer Syntax H dreamsphere_f Ro geom_par s_par delay m_par err_level Geometrical parameters geom_par r R r mm Radius of the transducer R mm Curvature radius of the transducer 7 3 7 Spherical Convex Transducer Syntax H dreamsphere_d Ro geom_par s_par delay m_par Geometrical parameters geom_par r R r mm Radius of the transducer R mm Curvature radius of the transducer 99 The DREAM ios 7 TRANSDUCER FUNCTION REFERENCE 7 3 8 Cylindrical Concave Transducer Syntax H dreamcylind_f Ro geom_par s_par delay m_par err_level Geometrical parameters geom_par a b R a x size of the transducer b y size of the transducer R Radius of the curvature 7 3 9 Cylindrical Convex Transducer Syntax H dreamcylind_d Ro geom_par s_par delay m_par Geometrical parameters geom_par a b R a x size of the transducer b y size of the transducer R Radius of the curvature 7 4 Input Parameters Common to the Array Functions 7 4 1 The Array Grid Matrix The positions of the array transducer elements are determined by the L x 3 grid matrix G The first column contain the center x positions of the elements the second the y positions and the third the z positions L is the number of elements respectively This approach is very flexible and allows for arbitrary array geometries that not is restricted to equally spaced linear or 2D arrays
6. On Windows XP this is done by first right clicking on My Computer and then selecting Properties gt Advanced Environment Variables gt New and sec ond add the MSSdk variable and the path to the Windows SDK that you use you may need to reboot to make the new variable visible On Windows Vista go to the start meny right click on Computer and then select Properties Advanced system settings Environment Variables New and add MSSdk and the path to the Windows SDK 3 Run the m script build_mexfiles_msvc m 4 Copy the files in the gui and help_m_files directories to your DREAM install directory 5 Add your DREAM install directory to your MATLAB path That is add addpath your_installation_dir to your matlab startup m file or use the menu in the MATLAB GUI 6 Copy the files pthreadGC2 d11 and 1ibfftw3 3 d11 to C WINDOWS System32 Method 3 Matlab s build in LCC compiler depreciated 1 Download the DREAM Toolbox full source package and uncompress it 2 Start MATLAB and select compiler with mex setup if you have not already done so Run the m script build_mexfiles_windows m gt au Copy the files in the gui and help_m files directories to your DREAM install directory 5 Add your DREAM install directory to your MATLAB path That is add addpath your_installation_dir to your matlab startup m file or use the menu in the MATLAB GUI Note the LCC compiler at least LCC for M
7. your system installed for Windows see Sections 4 5 4 and 4 5 5 you should be able to install DREAM by 1 Download the special DREAM source code file for the Octave package manager 2 type pkg install dream 2 x x tar gz at the Octave command line You should now be able to see the DREAM packege by typing pkg list at the Octave command line 4 5 Installation from Source To build the DREAM Toolbox from sources you need to have developer tools installed for your system compiler linker etc Start with downloading and uncompressing the full source DREAM 2 x x tgz file This file contains the source code the documentation the user manual and the html code for the web pages The build process is based on Makefiles both for C C code and for building the EXT X user manual and html documentation Therefore to build the documentation you need to have T X PTEX installed and furthermore to build the html documentation you also need the tex4ht and highlight tools 4 5 1 Build DREAM for Linux Unix There are three methods that can be used to build the DREAM Toolbox on unix from sources The first and simplest is to use the m script build_mexfiles_unix m the second is to use the bash script build_dream sh and the third is to manually edit the build configuration file Make inc and then compile the sources Method 1 Using the build_mexfiles_unix m script This is the simplest method but there is no optimization for the
8. 29 29 29 30 30 30 31 32 32 11 4 Model Based Ultrasonic Array Imaging e e e 11 4 1 The Matched Filter cocos ordre ee ededa 11 4 2 The Optimal Linear Estimator o es e ses ccc ssas eter pocoo sadas 12 The Graphical User Interface Matlab only 13 Known Issues Bibliography A Building the Pthreads Library for 32 and 64 bit Windows B Building the FFTW Library for 32 and 64 bit Windows 37 37 39 40 40 DREAM roro 3 SYSTEM REQUIREMENTS 1 Introduction HE DREAM Discrete REpresentation Array Modeling toolbox is an open source software released under the GNU General Public License GPL for both MATLAB and Octave for simulating acoustic fields radiated from common ultrasonic transducer types and arbitrarily complicated ultrasonic transduc ers arrays The DREAM toolbox enables analysis of beam steering beam focusing and apodization for wide band pulse excitation both in near and far fields The toolbox is also provided with a user friendly graphical user interface GUI The toolbox consists of a set of routines for computing discrete spatial impulse response SIRs for various single element transducer geometries as well as multi element transducer arrays Based on linear systems theory these SIR functions can then be convolved with the transducer s electrical impulse response to obtain the acoustic field at an observation point Using the DREAM toolbox one can simulate ultrasonic measurement
9. 8 0 8 hehe EN p 1 0 7 0 7 ry L L 0 6 0 6 ae ee i 0 5 0 5 Leido patO I 0 4 0 4 poi PEA 0 3 0 3 0 2 0 2 p 100 0 1 0 1 Po ee d A 85 04 03 02 01 0 01 Normalized width a Triangle 1 0 2 03 04 05 85 04 03 o2 01 0 01 Normalized width b Gaussian al 0 2 03 04 05 0 5 0 4 0 3 0 2 0 1 0 01 0 2 03 04 05 Normalized width c Raised cosine 1 0 9 0 9 0 8 0 8 0 7 y 0 7 0 6 2 0 6 j oap 0 4 J 0 3 0 3 f 0 2 0 2 4 0 1 0 1 A Bs 0 4 0 3 0 2 0 1 0 0 2 0 3 04 05 0 1 Normalized width e Clamped 85 0 4 0 3 0 2 0 1 0 01 02 03 04 05 Normalized width d Simply supported Figure 7 The pre defined apodization window functions in the DREAM toolbox There are three parameters that controls the apodization in the DREAM toolbox apod_met apod and win par The apod met parameter is string variable for selecting apodization method options are off No apodization 95 E oolbox TR N S U ER Fl I I V ud User defined apodization triangle Triangular window gauss Gaussian bell shaped window Taised Raised cosine window simply Simply supported clamped Clamped The second parameter apod is a vector of apodization weights that is used for the ud option Pass an empty matrix if one of the other options are used
10. Brien Synthetic aperture techniques with a virtual source element IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 45 196 207 1998 G S Kino Acoustic Waves Devices Imaging and Analog Signal Processing volume 6 of Prentice Hall Signal Processing Series Prentice Hall 1987 R Stoughton Source imaging with minimum mean squared error jasa 94 827 834 1993 F Lingvall T Olofsson and T Stepinski Synthetic aperture imaging using sources with finite aperture Deconvolution of the spatial impulse response J Acoust Soc America 114 225 234 2003 F Lingvall and T Olofsson On time domain model based ultrasonic array imaging 54 1623 1633 2007 F Lingvall A method of improving overall resolution in ultrasonic array imaging using spatio temporal deconvolution Ultrasonics 42 961 968 2004 20 The DREAM B_ BUILDING THE FFTW LIBRARY FOR 32 AND 64 BIT WINDOWS A Building the Pthreads Library for 32 and 64 bit Windows The DREAM toolbox uses pthreads POSIX threads to run computations in parallel on several cores cpus To run the parallel functions on Windows the Pthreads win32 library is used http sourceware org pthreads win32 The most current version of the Pthreads win32 library which is the one used by DREAM is version 2 8 0 2006 12 22 A 32 bit binary version of the library can be found at ftp sourceware org pub pthreads win32 The Mi
11. The last parameter win_par scalar is used for raised cosine and Gaussian apodization functions See also Section 10 1 7 5 Array Transducers 7 5 1 Array with Rectangular Elements Syntax H dream_arr_rect Ro geom_par G s_par delay m_par foc_met focal steer_met steer_par apod_met apod win_par err_level Geometrical parameters geom_par a b a Element size in x direction b Element size in y direction 7 5 2 Array with Circular Elements Syntax H dream_arr_circ Ro a G s_par delay m_par foc_met focal steer_met steer_par apod_met apod win_par err_level Geometrical parameters r Radius of the transducer elements 7 5 3 Array with Cylindrical Concave Elements Syntax H dream_arr_cylind_f Ro geom_par G s_par delay m_par foc_met focal steer_met steer_par apod_met apod win_par err_level Geometrical parameters geom_par la b r a Element size in x direction b Element size in y direction r Radius y direction DA DREAM n 8 PARALLEL PROCESSING SUPPORT Example linear array gx 10 1 10 gy zeros length gx 1 gz zeros length gx 1 ex gx gy gy gz 8z 0 gx gy gz 7 5 4 Array with Cylindrical Convex Elements Syntax H dream_arr_cylind_d Ro geom_par G s_par delay m_par foc_met focal steer_met steer_par apod_met apod win_par err_level Geometrical parameters geom_par a b r a Element size in x direction b Element size
12. corresponding sampling interval t Ts 2 tk Ts 2 Also as seen from the analytical solutions above the SIRs always have a finite length as the transducer has a finite size The sampled SIRs are therefore naturally represented by finite impulse response filters FIRs 15 DREAM 5 AN INTRODUCTION TO THE IMPULSE RESPONSE METHOD The effect of the sampling scheme 4 is illustrated in Figure 4 for two discs with radii 1 2 and 3 mm respectively where the sampling interval Ts was 0 04us In Figure 4 a the analytic SIR is shorter than e Sampled SIR Analytic SIR al 1600F 4 Sampled SIR 1600 Analytic SIR i 1400F 1400 t o m o o o o T T nN o o 1000 SIR Amplitude m s fos s SIR Amplitude m s 8 I 1 1 Hl 1 1 1 Hl 1 I 1 1 Hl 1 i 1 1 1 i I i i 1 I I I 1 1 i 1 1 I I i i i r i 5 33 5 33 2 5 33 5 600 600 400 400 200 200 3325 333 33 35 33 4 33 4 33 3 33 35 33 4 33 4 t us t us a Continuous and sampled spatial impulse responses of b Continuous and sampled spatial impulse responses of a circular disc with radius r 1 2 mm a circular disc with radius r 3 mm Figure 4 Illustration of sampling spatial impulse responses The continuous and sampled on axis SIRs for two discs with radii 1 2 and 3 mm respectively are shown where the sampling interval Ts was 0 04 us Cp 1500 m
13. in y direction r Radius y direction 7 5 5 Annular Array Syntax H dream_arr_annu Ro G s_par delay m_par foc_met focal apod_met apod win_par err_level Geometrical parameters G Vector of annulus radies The first element in G is the radius of the center element then G has two entries for each annulus the inner and outer radius Hence the length of G must be odd for the annular array The apod_met parameter has the following entries for the annular array function on Focusing on xy see Section 7 1 5 off No focusing ud User defined focusing 8 Parallel Processing Support Since the SIR computation for two different observation points is independent one can easily divide the observation points in sets and let a different process handle each set On a multiprocessor machine where each process or thread can run on a separate CPU simultaneously this will speed up the computations In the DREAM toolbox this is performed using POSIX threads the SIRs for each set is pueda in its own thread The DREAM functions with thread support has an extra parameter n_cpus and a _p in its function name For example to compute SIRs for a rectangular transducer on 2 CPUs use 97 qe E Toolbox DREAM 8 PARALLEL PROCESSING SUPPORT n_cpus 2 H dreamrect_p Ro geom_par s_par delay m_par n_cpus stop where n_cpus is an integer gt 1 To see if the two threads are running using Linux open new
14. matrix for e respectively The estima tor 23 has the property not found for the matched filter or for delay and sum methods namely that any beampattern can be compensated given that the signal to noise ratio is sufficient As a final not on model based imaging is that the matrices involved normally become rather large It is therefore highly recommended to used a tuned linear algebra library such as K Goto s BLAS library or the ATLAS library for example These libraries often have thread support so that all CPUs on the computer can be utilized An example of model based and matrix based delay and sum imaging can be found on the DREAM website see the model_base_example m file on the examples page 2R The DREAM oro 13 KNOWN ISSUES 12 The Graphical User Interface Matlab only To launch the DREAM Toolbox GUI type dream _ gui in the MATLAB Command Window and a graphical user interface will be raised as shown in Figure 9 After activating the user interface users can set F F Figure 9 The graphical user interface parameters compute SIRs and save and process the resulting SIR by using the graphical controls For setting of geometry parameters please also refer to the schematic diagram of transducer displayed in the center of the graphic interface After setting all the parameters clicking on the Compute button starts to compute SIR In addition the DREAM GUI provides several post processing operat
15. resulting waveform can faithfully represent the sampled measured waveform The analytical SIRs have an infinite bandwidth due to the abrupt amplitude changes that for example could be seen in the line and disc solutions above In some situations the duration of a SIR may even be shorter than the sampling interval T and it is therefore not sufficient to simply sample the analytical SIRs by simply taking the amplitude at the sampling instants since the SIR may actually be zero those time instants The SIRs are however convolved with a band limited normal velocity signal hence the resulting pressure waveform must also be band limited cf 2 Consequently we only need to sample the SIR in such way that the band limited received A scans are properly modeled In a sampled system the impulse responses are given at discrete time instants t given by the sampling period T and to faithfully represent the SIRs we need to collect all contributions from the continuous time SIRs in the corresponding sampling interval ty T 2 t Ts 2 A discrete version of the a time continuous SIR is then obtained by summing all contributions from the SIR in the actual sampling interval That is the sampled SIR is defined as 1 tk Ts 2 h r tk zj oa h r t dt 4 S k s The division by T retains the same unit m s of the sampled SIR as the continuous one The amplitude of the sampled SIR at time tg is then the mean value of the continuous SIR in the
16. systems for many configurations including phased arrays and measurements performed in lossy media The DREAM toolbox uses a numerical procedure based on based on the discrete representation DR computational concept 1 2 which is a method based on the general approach of the spatial impulse responses 3 4 2 Copyright HE DREAM toolbox is an open source software and the source code for the toolbox is freely re distributable under the terms of the GNU General Public License GPL as published by the Free Software Foundation http www gnu org See also the file COPYING which is distributed with the DREAM Toolbox The DREAM Toolbox can be downloaded at http www signal uu se Toolbox dream At this website you can also find information how to contact the authors and report bugs etc 2 1 Disclaimer The DREAM toolbox is distributed in the hope that it will be useful but WITHOUT ANY WARRANTY More specifically THE PROGRAM IS PROVIDED AS IS WITHOUT WARRANTY OF ANY KIND EITHER EXPRESS OR IMPLIED INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OR CONDITIONS OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE IN NO EVENT SHALL ANY OF THE AUTHORS OF THE DREAM TOOLBOX AND OR THE DEPARTMENT OF ENGINEERING SCIENCES AT UPPSALA UNIVERSITY SWEDEN OR THE INSTITUT D ELECTRONIQUE ET DE MICRU ELECTRONIQUE DU NORD IEMN DOAE UMR CNRS 9929 ECOLE CENTRALE DE LILLE FRANCE BE LIABLE FOR ANY SPECIAL INCIDENTAL INDIRECT OR CONSEQU
17. terminal window and use the command top You should see something like 17 10 15 up 62 days 21 18 4 users load average 0 77 0 26 0 16 80 processes 77 sleeping 3 running O zombie O stopped CPUO states 100 0 user 0 0 system 0 0 nice 0 0 iowait CPU1 states 100 0 user 0 0 system 0 0 nice 0 0 iowait Mem 6211732k av 5835092k used 376640k free Ok shrd 1280556k active 4156076k inactive Swap 4096496k av 420k used 4096076k free 0 0 idle 0 0 idle 284960k buff 5000568k cached PID USER PRI NI SIZE RSS SHARE STAT LC CPU MEM TIME COMMAND 29403 f1 25 O 75916 74M 11820 R 099 9 1 2 0 11 matlab 29404 f1 25 O 75916 74M 11820 R 199 9 1 2 0 11 matlab 29395 f1 15 0 1304 1304 968 R 2 0 3 0 0 0 00 top 1 root 15 O 472 460 4245 2 0 0 0 0 0 49 init 2 root RT 0 0 0 O SW 0 0 0 0 0 0 00 migration_CPUO 3 root RT 0 0 0 O SW 1 0 0 0 0 0 00 migration_CPU1 As one can see there are two MATLAB processes running on 99 9 instead on just one Note that there is an overhead when creating and running new threads If the distributed computations are very short the computations may not be faster for the parallel algorithm than the serial On uni processor computers the thread enabled functions may be slower than the non threaded functions due to this overhead if the hardware and software do not support hyper threading The functions currently available with parallel thread support is shown in Table 2
18. we need to consider both the forward process and the backward process As discussed in Section 5 1 Eq 2 the forward response can be divided in three parts the input signal u t the forward electro acoustical response h f t and the forward SIR h r t The backward response can similarly be divided in two parts the backward acousto electrical impulse response h t and the backward SIR h gt r Now consider an array with K transmit elements and L receive elements and contributions from a single observation point r z y a where 7 denotes the transpose operator The received signal y r t from the th receive element can be expressed Forward impulse response f K 1 yi r t Y OS ut o r s k 0 Backward impulse response b 17 a Oo hp r t APE elt h r t hp r t o r e t h r t o r e t where x denotes temporal convolution and e t is the noise for the lth receive element Note that the total forward impulse response is a superposition of the forward impulse responses corresponding to all transmit elements The object function o r is the scattering strength at the observation point r h t is the forward electrical impulse response for the kth transmit element he t the backward electrical impulse response for the lth receive element and u t is the input signal for the kth transmit element A discrete time version of 15 is obtained by sampling the impulse responses and by usi
19. 1 SIGNAL PROCESSING EXAMPLES T Temperture in degrees Celsius P Pressure optional unit Text string defining the pressure unit of arg 2 Pa bar at atm mmHg or psi optional S Salinity in parts per thousand optional 11 Signal Processing Examples 11 1 Double path Modeling Double path responses can be modeled as convolutions between the forward and backward responses 9 This operation can be time consuming when the number of observation points is large The DREAM toolbox has the threaded functions conv_p and fftconv_p that can be used to speed up this operation A typical example is H fftconv_p H_t H_r n_cpus Double path P fftconv_p H h_e n_cpus Electrical impulse response where we first compute the double path SIRs and then add convolve the double path electrical impulse response to get the double path propagation response matrix P 11 2 Synthetic Aperture Imaging The Synthetic Aperture Focusing Tech nique Synthetic aperture imaging SAI was developed to improve resolution in the along track direction for side looking radar The idea was to record data from a sequence of pulses from a single moving real aperture and then with suitable computation combine the signals so the output can be treated as a much larger aperture The first synthetic aperture radar SAR systems appeared in the beginning of the 1950 s 10 11 Later on the method has c
20. 7 4 2 Array Focusing The array focusing has an extra option ud compared to the focusing methods described in Sec tion 7 1 5 off focusing not used gt x see Section 7 1 5 y see Section 7 1 5 xy see Section 7 1 5 x y see Section 7 1 5 ud user defined focusing When user defined focusing is used the focal parameter is a vector of focusing delays in us Each element in focal then delays the signal to the corresponding element in the array given by the grid matrix DA DREAM roro 7 TRANSDUCER FUNCTION REFERENCE 7 4 3 Beam Steering Parameters The beam steering in the DREAM toolbox is controlled by the two parameters steer_met and steer_par The steer met is a text string with four alternatives off x y and xy The steer par is a two element vector steer_par theta phi where theta deg is the x direction steer angle and phi deg the y direction steer angle 7 4 4 Apodization Parameters The DREAM toolbox has five pre defined apodization windows that can be used for the array functions Wtriangle 1 LL E 10 Wgauss T p exp pr T vax 11 Wraised T p p cos r7 Tmax 12 Wsimply r 1 a 13 Welampead T 1 17 riax 14 Additionally to the pre defined apodizations one can have a user defined apodization weights Figure 7 show some examples of these function 1 SSS 0 9 na A 012 I 0
21. ENTIAL DAM AGES OF ANY KIND OR DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE DATA OR PROFITS WHETHER OR NOT THE AUTHORS OF THE DREAM TOOLBOX HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES AND OR ON ANY THEORY OF LIABILITY ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE 3 System Requirements 1 MATLAB gt 7 1 or 2 Octave gt 2 9 12 gt 3 0 0 recommended lThe graphics routines have been in under heavy development in recent versions of Octave The plotting and image routines in Octave 3 0 0 and above are therefore much more compatible with Matlab now then it used to be The example DREAM 0 4 INSTALLATION 3 FETW gt 3 0 1 optional 4 Pthread 4 Installation HE DREAM Toolbox can be installed both using pre compiled binaries and from source code Bi naries are currently available for Linux x86 x86_64 Windows x86 and for Intel Macs Mac OS X The binaries are compiled using generic compiler flags and without support for the fftw library for the transducer functions and should therefore run on most setups If you want higher performance then it is recommended that you compile DREAM from source There is a bash script and m files included in the source distribution to facilitate building the toolbox and furthermore the Makefiles used in build process can easily be edited for further fine tuning of the performance 4 1 Binary Installation Matlab only 1 Dow
22. J surface elements ASo AS AS 1 Second let w denote an aperture weight and Rj r r the distance from the jth surface element to the observation point The discrete SIR can now be approximated by J 1 E eee eee h r tk on y J R p J AS j 0 II J 1 Y 945 te Ri cp dy j 0 1R DREAM xr 5 AN INTRODUCTION TO THE IMPULSE RESPONSE METHOD Observation point Figure 5 Geometry and notations for the discrete representation method where d is a user defined focusing delay and tk kT for k 0 1 K 1 The scaling factor wjAS 2n R 6 Qj in 5 represents the amplitude of the impulse response for an elementary surface at r excited by a Dirac pulse Hence the total response at time tz is a sum of contributions from those elementary surface elements AS whose response arrive in the time interval tg Ts 2 tk T 2 The accuracy of the method depends on the size of the discretization surfaces AS It should however be noted that high frequency numerical noise due to the surface discretization is in practice not critical since the transducer s electrical impulse response has a bandwidth in the low frequency range for a further discussion see 2 Also these errors are small if the elementary surfaces AS are small The DR method is very flexible in the sense that beam steering focusing apodization and non uniform surface velocity can easily be included in the
23. User Manual for the DREAM Toolbox Version 2 1 3 An ultrasound simulation software for use with MATLAB and GNU OCTAVE Fredrik Lingvall November 13 2009 E mail Fredrik Lingvall ifi uio no Contents 1 Introduction 5 2 Copyright 5 Td Derio ca er rra aa as AA a ri Od 3 System Requirements 5 4 Installation 41 Binary Installation Matlab only oo oras ri a eee ee 4 2 Windows Specific Installation Notes o 002 e o 4 3 MacOS X Specific Installation Notes 4 4 4 Octave Specific Installation Notes o e 4 5 Installation from S0urte 4 0665 bbe da ee ee eae ee a 491 Build DREAM for Linux Unix 2 642 Fa ba REE KARR RR ee 4 5 2 Build the DREAM mex files for MacOS X Intel Macs 4 5 3 Build the DREAM Matlab 32 bit mex files for Windows 4 5 4 Build the DREAM Octave 32 bit oct files for Windows using the MinGW Compiler 10 4 5 5 Build the DREAM 32 bit Octave oct files for Windows using the MSVC compiler depreciated 11 OO ON NNN DD SF 4 5 6 Build the DREAM matlab mex files for 64 bit Windows 11 4 5 7 Build the DREAM Octave oct files for 64 bit Windows 12 4 5 8 Compile with FFTW support for the Attenuation Code 12 5 An Introduction to The Impulse Response Method 12 5 1 The Baffled Piston Model and the Rayleigh integral o o 13 5 2 Discrete time Spatial Imp
24. _files directories to your DREAM install directory 6 Add your DREAM install directory to your MATLAB path That is add addpath your_installation_dir to your matlab startup m file or use the menu in the MATLAB GUI 4 5 3 Build the DREAM Matlab 32 bit mex files for Windows Method 1 Using the MinGW Gnumex Tools 1 Download the DREAM Toolbox full source package and uncompress it 2 Install MinGW and the Gnumex tools see http www mingw org and http gnumex sourceforge net 3 Gnumex is normally setup by running the gnumex m script which is located in the main Gnumex directory from the Matlab promt which generates a mexopts bat file for the Matlab mex command The windows mexopts directory contains three pre build bat files for MinGW 3 4 5 and Gnumex 2 1 0 which is used to build the toolbox and link with the fftw and Pthread Win32 libs You need to edit the mexopts_mingw bat mexopts_pthread_mingw bat and mexopts_pthread fftw_mingw bat files for your installation that is set paths to your DREAM source directory MinGW directories and Gnumex directories respectively The lines you need to make changes in are indicated with numbers 1 7 in the respective bat file 4 Start MATLAB and run the m script build_mexfiles_mingw m in the main DREAM source direc tory 5 Copy the files in the gui and help_m_files directory to your DREAM install directory 6 Add your DREAM install directory to your MATLAB path That i
25. ad support IR DREAM motor 10 MISC FUNCTIONS 9 Analytic Transducer Functions The DREAM Toolbox has two new time continous analytic functions and one sampled analytic function for circular and a rectangular transducers respectively 4 6 The parameters for the functions Y circ_sir Ro geom_par delay s_par m_par Y rect_sir Ro geom_par delay s_par m_par Y scirc_sir Ro geom_par delay s_par m_par n_int are similar to the other DR based transducer functions except for the sampled analytic circular function scirc_sir which has a parameter n_int that determines the number of points to use in the numerical temporal integration for each sampling interval cf Eq 4 10 Misc Functions 10 1 Apodization Windows The DREAM toolbox includes function w dream_apodwin apod_met a win_par that can be used to compute apodization weights using the methods described is Section 7 4 4 The input parameters are apod met Text string for selecting apodization method options are off ud triangle gauss raised simply and clamped a Is the number of points of the apodization window win par Scalar parameter for raised cosine and Gaussian apodization functions 10 2 Attenuation Response The function H dream_att Ro s_par delay m_par can be used to compute only the impulse response s that is due to attenuation The input parameters for dream_att a
26. ager is not thread safe at least not R2007b and older The functions that use the fftw library may therefore crash if n_cpus gt 1 A workaround is to set the env variable MATLAB_MEM MGR system i e export MATLAB_MEM MGR system e The file mex_sum_fftconv_p c do not compile unless MATLAB gt R2006b is installed The problem is that mwSize must be defined in matlab extern include matrix h sum_fftconv_p compiles for Octave e The computation of responses for lossy media is rather time consuming the computation time can be as large as a factor of 1000 times longer than for loss less media This due to the fact that the frequency domain attenuation response is computed and an inverse FFT is performed for every surface element dxxdy of the transducer surface IQR DREAM roro REFERENCES References 1 B Piwakowski and B Delannoy Method for computing spatial pulse response Time domain ap 2 13 14 15 16 17 18 19 20 proach J Acoust Soc America 86 2422 32 1989 B Piwakowski and K Sbai A new approach to calculate the field radiated from arbitrarily struc tured transducer arrays IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 46 422 40 1999 G E Tupholme Generation of acoustic pulses by baffled plane pistons Mathematika 16 209 224 1969 P Stepanishen Transient radiation fom pistons in an infinite planar baffle
27. arried over to ultrasound imaging in areas such as synthetic aperture sonar SAS 12 medical imaging and nondestructive testing 13 14 where the method is often called the synthetic aperture focusing technique SAFT The conventional time domain SAFT algorithm performs synthetic focusing by means of coherent summations of responses from point scatterers along hyperbolas These hyperbolas simply express the distances or time delays from transducer positions in the synthetic aperture to the observation points see illustration in Figure 8 More specifically to achieve focus at an observation point A 2m the SAFT algorithm time shifts and performs a summation of the received signals y x t measured at transducer positions x for all n in the synthetic aperture The time shifts which aim to compensate for differences in pulse traveling time are simply calculated using the Pythagorean theorem and the operation is commonly expressed in the continuous time form 15 2 hy em n ns n 24 2 16 o U Zm ee y x z T Un Zin 16 where o 2 Zm is the beamformed image The DREAM Toolbox has two functions saft and saft_p respectively that performs the SAFT operation with linear interpolation Y Y saft B To delay s_par m_par Ro a saft_p B To delay s_par m_par Ro a n_cpus lOLinear scanning of the transducer is assumed here 292 DREAM wo 11 SIGNAL PROCESSING EXAMPLES Scanning XQ direct
28. atlab R2007b cannot build the parallel mex functions since the compiler cannot parse the Pthread Win32 header files All parallel functions will therefore be unavailable if you are using the LCC compiler 4 5 4 Build the DREAM Octave 32 bit oct files for Windows using the MinGW Compiler The pkg source can be build also on Windows with resent versions of Octave tested with Octave 3 2 3 MinGW 4 4 0 To do this using the native Windows Octave from octave forge you only need to install Octave since fftw the MinGW compiler and the pthread libs are included in the Octave package 1 Download the DREAM Toolbox pkg source package i e the file dream 2 x x tar gz 2 Download the Windows Octave installer 3 Install Octave in C Octave do not install in C Program Files Octave since the mkoctfile script that is used to compile the C code in the DREAM toolbox do work well with white spaces in the path the default install location should be OK 4 Build and install the DREAM Toolbox with pkg install dream 2 x x tar gz DREAM roro 4 INSTALLATION 4 5 5 Build the DREAM 32 bit Octave oct files for Windows using the MSVC compiler depreciated This section describes how to build the DREAM oct files for Windows using the MSVC compiler But note that as of spring 2009 Octave binaries build with the MSVC compiler are no longer available at octave forge due to license issues It is therefore recomended that the MinGW compiler is
29. b Octave do not make a copy of a matrix unless it is changed after X Y assignment 10 3 3 Computing Array Responses for Arbitrary Input Signals The pressure response at an observation point r can be computed by super imposing the responses from the individual array elements Assume that we have an array with K transmit elements The pressure response p r t is then given by KE p r t hESE r t REE ult 15 k 0 BR where h SIR r t is the forward SIR for the kth transmit element h f t is the forward electro acoustical impulse response and u t is the kth input signal The DREAM Toolbox has a function sum_fftconv_p to facilitate computation of discrete array responses with arbitrary input signals Similar to the fftconv_p function the sum_fftconv_p function uses a FFT based algorithm to compute the convolutions The sum_fftconv_p function performs an operation similar to the code YF zeros M K 1 N for 1 1 L for n 1 N YF n YF n f t A n 1 M K 1 fft B 1 M K 1 end end Y real ifft Y where A is a 3D matrix Y Y sum_fftconv_p A B n_cpus sum_fftconv_p A B n_cpus wisdom_str sum_fftconv_p A B n_cpus Y sum_fftconv_p A B n_cpus Y wisdom_str 27 DREAM coves 10 MISC FUNCTIONS Input parameters A An M x N x L three dimensional matrix BA K x L matrix n_cpus Number of threads to use where n_cpus must be greater or equal to 1 wisdom_str Optional parameter see Sec
30. b files These lib files can be generated using the windows bat files found in the windows d11 and windows d11_64 folders respectively B Building the FFTW Library for 32 and 64 bit Windows For conveniance we have also included the sources for the FFTW library and two scripts to build the library for both 32 and 64 bit Windows The bash scripts uses MinGW w32 and MinGW w64 cross compiler tool chains respectively Change directory to the windows folder and run BUILD MINGW FFTW sh to build for 32 bit Windows or BUILD MINGW_64 FFTW sh for 64 bit Windows The two build scripts are based on the corresponding ones at the FFTW site adapted for building DREAM on Windows The scripts install the libraries in the windows d11 and windows d11_64 folders respectively Similary to the Pthreads win32 lib you need to build the 1ib files if you intend to use these libs with one of the MSVC compilers These lib files can be generated using the corresponding windows bat files found in the windows d11 and windows d11_64 folders respectively AN
31. cer e 7 4 Input Parameters Common to the Array Functions 2000 741 The Array Gid Matrix oo mece os RA Re ee we ee E TA PE FOCUSING 0 ad o a Bee AA ae Se ee Ee a a 7 4 3 Beam Steering Parameters ee 7 4 4 Apodization Parameters tacaud a paeta kaa ee To Array Transducers gt or aa da E A A a a 7 5 1 Array with Rectangular Elements aoao a e 7 5 2 Array with Circular Elements a e ss urarea ea rewan ie 7 5 3 Array with Cylindrical Concave Elements o a 7 5 4 Array with Cylindrical Convex Elements o oaoa a a T50 Aula Anmgy oler read a Parallel Processing Support Analytic Transducer Functions 10 Misc Functions 10 1 Apodization Windows s sd 0 680484 bb bee OEE REE e a a 10 2 Attenuation Response soosoo 10 3 One Dimensional Matrix Convolution Functions e a 10 3 1 Using Pre computed FFTW Plans 2 0 eo osi a lt lt de 10 32 Using the In place Mode 2 co aegea a e ee a a ga 10 3 3 Computing Array Responses for Arbitrary Input Signals 10 4 Parallel Metrix CORF o c po d we oi doana i a e GH 10 5 The Speed of Sound in Water 11 Signal Processing Examples 11 1 Dewblepath Modeling osas 206 pn eoe EA e OE ie Se a wR eS 11 2 Synthetic Aperture Imaging The Synthetic Aperture Focusing Technique 11 3 Delay aia sum Image 6 kee ee ee ee ek ee a ee eS Ee 27 29
32. ctave path s That is add addpath your_installation_dir to your matlab startup m file and or octaverc file Method 3 Manual configuration I 2 Copy Make default to Make inc and open the Make inc file with a text editor Change the paths for Matlab and or Octave in Make inc to fit your installation Change INSTALL_DIR MEX_EXT if you use MATLAB CFLAGS and OCTVER if you use Octave in Make inc to fit your architecture If you don t have both Matlab and Octave then open the Makefile and remove the corresponding software on the line all matlab octave doc that you don t use Type make Add your DREAM install dir to the MATLAB Octave path s That is add addpath your_installation_dir to your matlab startup m file and or octaverc file 4 5 2 Build the DREAM mex files for MacOS X Intel Macs There is currently only one method to build the DREAM mex files for MacOS X and that is to use the build mexfiles_unix m script the Makefiles do not currently work under Mac OS X 1 2 Install fftw if it is not already installed Start MATLAB and select compiler gcc is recommended with mex setup if you have not already done so DREAM roro 4 INSTALLATION 3 Remove the ansi flag from your matlab R200Xx mexopts sh file the DREAM sources contain C style comments which will not compile with ansi 4 Run the m script build_mexfiles_unix 5 Copy the files in the gui and help_m
33. ctions in Appendix A The fftconv_p and sum_fftconv_p use the FFTW3 library see Section 10 3 A Windows version of this library can be found at http www fftw org install windows html but it is now also available scripts in the DREAM toolbox now uses these new features in Octave and it is therefore recommended to install a recent version of Octave However the transducer functions in DREAM will probably also work with older versions of Octave 2The attenuation code in DREAM makes heavily use of FFTs If the optimized FFTW is installed then DREAM can be configured to use this lib 3If you want to use the parallel threaded DREAM functions in Windows you need to install the Pthreads Win32 library DREAM varo 4 INSTALLATION on the DREAM web page Copy the 1ibfftw3 3 d11 file to C WINDOWS System32 If you want to build the FFTW library for Windows from source then you can find instructions in Appendix B To install DREAM for Octave on Windows see Sections 4 5 4 and 4 5 5 4 3 MacOS X Specific Installation Notes The fftconv_p and sum_fftconv_p functions use the FFTW3 library see Section 10 3 Instructions for installing fftw on MacOS X can be found at http www fftw org install mac html 4 4 Octave Specific Installation Notes As mentioned above the DREAM Toolbox must be installed from sources for Octave Recent versions of Octave have a package manager tool pkg for that purpose Given that you have the developer tools for
34. dows version of fftconv_p is linked to the FFTW lib which as previously described can be found at ftp ftp fftw org pub fftw fftw3win32mingw zip 10 3 1 Using Pre computed FF TW Plans To speed up computation of repeated fftconv_p operations of the same size one can use pre computed fftw plans First compute the plan for the corresponding vector length tmp wisdom_string fftconv_p A 1 B 1 n_cpus then use the plan in consecutive computations of the same size for n 1 N Compute new A and B here Y fftconv_p A B n_cpus wisdom_string end The time consuming call to fftw plan functions is then avoided at each call to fftconv_p inside the loop 10 3 2 Using the In place Mode If the involved matrices are large then memory allocation can be time consuming To alleviate this problem both conv_p fftconv_p and sum_fftconv_p see Section 10 3 3 have an in place mode that ay DREAM recive 10 MISC FUNCTIONS uses a pre allocated output matrix hence memory allocation for the large output matrix Y is avoided For the conv_p and fftconv_p functions the in place operation has three modes and respectively The default mode Y fftconv_p H u n_cpus for n 2 N Compute new H and u here fftconv_p H u n_cpus Y end Note the in place mode have the side effect that in the code X Y fftconv_p H u n_cpus Y both X and Y will be altered since Mala
35. e medium m s alfa Attenuation coefficient dB cm MHz Note if alfa 4 0 then the SIRs are compensated for attenuation Note that the attenuation calculation involves a computation of an inverse discrete Fourier transform of length nt for every surface element dxxdy 2 This results in a longer computation time compared to when alfa 0 See also Section 10 2 7 1 5 Focusing parameters The focusing in the DREAM toolbox is controlled with the two parameters foc_met and focal The foc_met parameters is a text string that selects the focusing method options are off focusing not used x focus in z only x 23 cp gt y focus in y only yu 23 Cp xy focus in both x and y oF ye a 23 Cp x y focus in 1 y yP 23 Cp This type of focusing is used for the two single transducer functions dreamrect_f and dreamcirc_f see Section 7 3 and for the array functions Section 7 5 The spherical and cylindrical transducer functions also use focusing but there focusing is controlled by a single parameter R see Sections 7 3 6 7 3 7 7 3 8 and 7 3 9 7 1 6 Error Handling There are three levels of error reporting for the transducer functions An error typically occur when the SIR do not fit within the time window defined by the delay sampling period and length parameters The levels are controlled by the optional err_level parameter which is a text string with the following alternatives 1 i
36. gnore Here an error is silently ignored 2 warn An error message is printed but computation is not stopped 3 stop An error message is printed and the computation is stopped The error message contains a number that tells how many samples outside the time window the SIR is The default error level is stop if the err_level is omitted 7 2 Output Parameters Common to all Transducer Functions 7 2 1 The SIR Output Argument The first output argument of transducer functions H is a matrix or vector containing the spatial impulse response s H dreamx xx Each column H contain the SIR for the corresponding entry in the observation point input matrix Ro see Section 7 1 1 ey The DREAM io 7 TRANSDUCER FUNCTION REFERENCE 7 2 2 The Error Output Argument The second optional output argument err is negative if an error has occurred and 0 otherwise H err dream If for example err_level ignore then no error message will be printed but err will be negative if an error occurred so the error can be detected This is useful for displaying error dialog boxes in GUIs for example 7 3 Single Element Transducers As mentioned above all single element transducers are centered at r 0 0 0 There is however no loss in generality since the response at other transducer positions can simply be obtained by offsetting the coordinate system after computation 7 3 1 Line strip Tran
37. id baffle as illustrated in Figure 1 then the baffle S will not contribute to the field The pressure at an observation point r is then described by the Rayleigh integral 0000 tt Eolas ato Sr 85 2r r ro f t to r ro cp o valto f AZ dSpdto a p valto e t to dto p ont x hk r t to where it is where we for simplicity have assumed that the normal velocity v r9 t vn t is uniform on the transducer s surface Sh The Rayleigh integral formula 1 simply states that the acoustic field at an observation point is the sum of the contributions from all points of the active area of the transducer The impulse response Af r t in Eq 1 is usually referred to as the forward spatial impulse response SIR The normal velocity vn t depends on both the input signal u t and the electro acoustical properties of the transducer which can be described with the forward electrical impulse response h t Thus the pressure at r can be expressed by the convolutions of the input signal and the two forward impulse responses according to p r t h r t x h t x u t 2 Double path pulse echo responses can be treated in a similar way by convolving the forward response 2 with the backward electrical acousto electrical response and the backward SIR for a point source at r Analytical solutions to SIRs exist for a few geometries but one must in general resort to numerica
38. ion Tn TL 1 Th Zm Figure 8 Typical measurement setup for a SAFT experiment The transducer is mechanically scanned along the z axis and at each sampling position n n 0 1 L 1 a data vector A scan of length K is recorded The distance between the transducer at n z 0 and the observation point vA 2m is given by R Input parameters B KxL Ultrasonic B scan data matrix To A matrix of the form xol yol zo2 xo2 yo2 zo2 xoL yoL zoL where L is the number of transducer positions delay A scalar or vector of starting point s of the A scans in B n_cpus Number of threads to use n_cpus must be greater or equal to 1 11 3 Delay and sum Imaging The SAFT method described in Section 11 2 is a special case of methods based on so called delay and sum imaging DAS The simple idea is just to compensate for the double path propagation delay from each transmitter receiver to each observation point and then perform a coherent summation This operation is essentially based on an geometrical optics approach and is analogous to the operation of an acoustical lens 16 The DREAM Toolbox has two functions to facilitate matrix based delay and sum processing The two DAS functions das and das_arr is similar to the transducer functions in the sense that they return a matrix with responses corresponding to each observation point The difference from the transducer functions is that only the time dela
39. ions to process the SIRs including computing pressure response computing the spectrum of the SIR and convolving the SIR with an excitation signal Notice that if users tick the checkbox of pressure response the spectrum and convolution operations will be performed on the pressure instead of on the SIR The parameters and resulting SIR can be stored in an mat file by clicking on the button of Save The parameters settings can then be restored by loading the file using the Load button 13 Known Issues e On Windows platforms the MEX files can not be aborted by pressing CTRL C since Windows lacks real asynchronous signals see http www mathworks com support solutions data 1 188VX html Therefore when CTRL C is pressed using Windows the operation is interrupted after the MEX file has finished e On Linux x86 platforms the MATLAB release 14 library matlab sys os glnx86 libgcc_s so seems to be buggy causing MATLAB to abort when a mexErrMsg call is done within a MEX file The threaded functions uses the mexErrMsg function when CTRL C is pressed A work around is to set the environment variable LD_PRELOAD to point to a working library If you for example are using gir DREAM coves 13 KNOWN ISSUES gcc 3 4 4 then you can set export LD_PRELOAD usr 1ib gcc i686 pc linux gnu 3 4 4 libgcc_s so or rename matlab sys os glnx86 libgcc_s so and copy or link a working libgcc_s so to the matlab sys os glnx86 directory e Matlab s memory man
40. l methods Also these time continuous solutions are normally not practical since all acquired signals the data are normally sampled and time discrete models are therefore needed sampling of time continous SIRs is discussed in Section 5 2 Before we discuss sampled SIRs and the particular method use by the DREAM Toolbox let us consider a case where there exist an analytical solution Example 1 The SIR for a Circular Disc The SIR of a circular disc see illustration in Figure 2 has an analytical solution 4 which can be divided in two cases i when the observation point is inside 12 DREAM 5 AN INTRODUCTION TO THE IMPULSE RESPONSE METHOD Y Figure 2 Geometry of a a circular disc source the aperture of the disc x y lt a where a is the transducer radius and ii when the observation point is outside the aperture The disc is assumed to be located in the x y plane centered at x y 0 If we let r denote the distance in the x y plane from the center axis of the disc to the observation point r yz y then the circular disc SIR is given by forr lt a 0 t lt t Cp t lt t lt ti h r t c g t ttt a c cos Oo fae y ti lt t lt ta 0 t gt to 3 forr gt a 0 t lt t Je 1 at tittp a cp h r t 4 2 cos ee i ty lt t lt ta 0 t gt t where t z cp is the earliest time that the wave reaches the observation point r when r lt a tr r cp and tio tz4 1 2 are the
41. l bat C Octave bin octave 3 0 1 exe to the file change the path to the actual version of Octave that you use Start Octave by running the bat file created above Build and install the DREAM Toolbox with pkg verbose install dream 2 x x tar gz Get the pthreadGC2 d11 file from http sourceware org pthreads win32 version 2 8 0 or from the DREAM web page and copy it to C WINDOWS System32 4 5 6 Build the DREAM matlab mex files for 64 bit Windows If you have an older 64 bit Matlab installation eg 2007x then follow these steps 1 2 Install MSVC 2008 Express Edition SP1 Install the Windows SDK The current version is Windows SDK for Windows Server 2008 and NET Framework 3 5 Remember to select the X64 Compilers and Tools when installing the SDK 11 DREAM 5 AN INTRODUCTION TO THE IMPULSE RESPONSE METHOD 3 If you are using a different Windows SDK version than 6 1 then you need to set the correct path in the bat file windows mexopts mexopts _msvc_64 bat 4 Get the 64 bit versions of fftw and Pthread win32 from http sourceforge net projects mingw w64 and http www fftw org respectively or from the DREAM web page and copy them to C WINDOWS System32 If you have Matlab 2008b or above then read and follow the instructions in Mathworks FAQ http www mathworks fr support solutions en data 1 6IJJ3L index html solution 1 6IJJ3L Then run the build_mexfiles_windows m script 4 5 7 B
42. nGW w64 project has a patch to build the Pthreads win32 lib for 64 bit Windows and there are some more 64 bit patches at http www cadforte com wiki index php Pthreads To facilite building the lib we have included our own experimental patch which is a combination of the patches above with some minor changes and the source code for the Pthreads win32 lib in the source code packge of the DREAM toolbox There are also two bash build scripts which can be used for building the 32 bit and 64 bit libs respectively This is tested using the MinGW w32 and MinGW w64 cross compiler tool chains on Linux After uncompressing the DREAM source code packge you can find these files in the windows folder Given that you have installed the MinGW w32 cross compiler you can build the 32 bit Pthreads win32 with build_pthreads_win32 sh This will build the pthreadGC2 d11 file and copy it the pthread def file and the header files pthread h sched h and semaphore h to the windows d11 folder For 64 bit windows you first need to install the MinGW w64 cross compiler and then the script build_pthreads_win64 sh will copy the Pthreads win32 sources patch them for 64 bits support and build the lib The 64 bit lib the pthread def file and the header files pthread h sched h and semaphore h will be installed in the windows d11_64 folder Note if you intend to use these libs with one of the MSVC compilers then you also need the corre sponding li
43. ng discrete time convolutions If we consider N observation points then the received discrete waveform from a target at the nth observation point rn n Yn Zn can be expressed as y h 0 ter 18 where the column vector hi is the discrete system impulse response for the lth receive element The vector o represents the N scattering amplitudes in the region of interest and the notation n denotes the nth element in o 1 To obtain the received signal for all observation points we need to perform a summation over n which equivalently can be expressed as a matrix vector multiplication according to y de h 0 n e n EN hy REN ie o e 19 P o amp ll Here all vectors are by convention column vectors 2The vector o can easily be rearrange to form an image when two dimensional imaging is considered 20 25 DREAM roro 11 SIGNAL PROCESSING EXAMPLES which gives us a liner model for the data for one receive element To obtain a model for all elements we can append all L receive signals y into a single vector y and we finally have linear model for the total array setup Yo Po eo yi P el y o 20 YL 1 Pr i e L 1 Po e for the total array imaging system 20 The propagation matrix P in 20 now describes both the transmission and the reception process for an arbitrary focused array Note that the position of the observation points and the corresponding scattering amplitudes re
44. nload the dream xxx 2 x x tgz file or dream xxx 2 x x zip file using your favorite browser where xxx replaced by the hardware architecture unix 32 64 win or maci and the 2 x x is replaced by the actual version number of the toolbox 2 Copy the file to a suitable directory on your disk and uncompress the file Windows Use Winzip or Winrar Linux Type tar xvzf dream xxx 2 x x tgz or gunzip dream xxx 2 x x zip 3 Add the new directory into the MATLABpath This can be performed by choosing the Set Path command from the File menu MATLAB only or using the addpath command On Linux you can add the line addpath your_installation_dir to your startup m file Note since the oct API often changes between releases of Octave the binaries will probably only work for the version of Octave that they were compiled for For this reason binaries for Octave are no longer available and you need to install the toolbox from source which easily can be done with the Octave pkg command see Section 4 4 4 2 Windows Specific Installation Notes If you want to use the parallel threaded DREAM functions you need to install the Pthreads Win32 library Download the library from http sourceware org pthreads win32 and put the pthreadGC2 dll file in a suitable directory such as C WINDOWS System32 this file is now also available on the DREAM web page If you want to build the Pthreads library for Windows from source then you can find instru
45. nse for a circular transducer using water as the propagation medium with a sound speed c 1500 m s We start by setting the sampling frequency and defining the points of interest the so called observation points The observation points are located on a line at z 10 mm from 1 50 mm with 1 mm between them Fs Ts 10 Sampling freq in MHz 1 Fs Observation point s Depth z 10 mm Points along x axis d 1 mm xo 0 d 50 0 50 mm yo zeros length xo 1 zo z xones length xo 1 Ro xo yo zo Then we need to define the discretization parameters for both the transducer surface and the temporal sampling 12 The DREAM roro 7 TRANSDUCER FUNCTION REFERENCE Descretization parameters dx 0 03 Umm dy 0 03 mm dt Ts us nt 400 Length of spatial impulse response vector s_par dx dy dt nt We must also define the sound speed of the medium normal velocity and attenuation Here we choose an attenuation free medium a 0 and a unit normal velocity Material parameters v 1 0 Normal velocity cp 1500 Sound speed alfa 0 Absorbtion dB cm MHz m_par v cp alfa The size of the transducer must also be defined here we use a circular transducer with a 5 mm radius Geometrical parameters r 5 Radius mm geom_par r Finally we set the start point of the SIR and call the DREAM function dreamcirc t
46. o compute the discrete SIRs Delay t_z z 1e3 cp delay 0 Start at 0 us delay t_z Start at t z us H dreamcirc Ro geom_par s_par delay m_par stop 7 Transducer Function Reference HE transducer functions are implemented as MATLAB mex functions and Octave oct functions a mex oct function is pre compiled code that is dynamically linked to MATLAB Octave at run time This greatly increases the computation speed compared to using ordinary m files since the DR concept see 2 uses for and while loops extensively An overview of the transducer functions can be found in Table 1 By convention a transducer function name ending with _ is a focused transducer or has focused transducer elements and a transducer function name ending with _d is defocused convex transducer The transducer functions can be divided in two groups single transducer functions and array func tions The names of both groups starts with dream and the array functions are distinguished from single transducer functions by _arr_ Note that arbitrary arrays with mixed forms of transducer elements can be modeled using the single transducer functions and then adding their corresponding responses 7 1 Input Parameters Common to all Transducer Functions 7 1 1 Observation Point s Parameter The transducer functions can compute SIRs for multiple observation points The observation points are given by a N x3 matrix Ro we
47. presented by the vector o is not restricted to a regular two dimensional grid which is often used in ultrasonic imaging Furthermore the array elements can in fact similar to the observation points be positioned at arbitrary locations in tree dimensional space space Thus the model 20 can also be used to model two dimensional arrays as well as to model array responses in tree dimensional space Also note that the noise vector e describes the uncertainty of the model 20 The noise e does not only model the measurement noise but also all other errors that we may have such as multiple scattering effects cross talk between array elements non uniform sound speed in the media etc 11 4 1 The Matched Filter The matched filter has the property of maximizing the signal to noise ratio at a single point The matched filter for each observation point is given by 18 6 P y 21 Note that the structure of the matched filter is similar to delay and sum processing which also can be expressed as a matrix vector multiplication see the model_based_example m on the DREAM website 6 D y 22 where the delay matrix D has ones in the positions corresponding the the propagation delays and zeros otherwise 11 4 2 The Optimal Linear Estimator The optimal linear estimator or the Wiener filter is given by 17 19 C P PC P C ly 23 P Or P O I POr y where C is the covariance matrix for o and Ce is the covariance
48. propagation times corresponding to the edges of the disc that are closest and furthermost away from r respectively Noticeable is that the pulse amplitude of the on axis SIR is constant regardless of the distance to the observation point The duration of the on axis SIR is given by t a cp at z 0 As the distance increases the duration t tz of the SIR becomes shorter and for large z it approaches to the delta function The transducer size effects are therefore most pronounced in the near field This is illustrated in Figure 3 where the on axis SIRs at z 20 and z 80 mm respectively are shown The duration at z 20 is longer than that of z 80 and if the distance z increases then the on axis SIR will approach to a delta function cf Figures 3 a and b As mentioned above there exist no analytical analytical solutions for many transducer geometries and in such situations numerical methods must be used The DREAM Toolbox uses a method based on the discrete representation DR computational concept 1 2 The DR method is very flexible in the sense that complex transducer shapes as well as arbitrary focusing methods easily can be modeled Another benefit of the DR method is that the SIRs are directly computed in a discrete form which is convenient since this directly allows for digital signal processing The DR method is described in Section 5 3 below but first we will discuss sampling of spatial impulse responses
49. re Ro See Section 7 1 1 s_par dt nt See Section 7 1 2 delay See Section 7 1 3 m_par cp alfa See Section 7 1 4 20 DREAM roro 10 MISC FUNCTIONS 10 3 One Dimensional Matrix Convolution Functions The conv_p and fftconv_p functions computes the one dimensional convolution of the columns in a matrix A and matrix or vector B using one or more threads These functions are typically used to compute single path or double path pulse echo responses for a large number of observation points and thus avoiding a slow for loop using the conv function that only takes vector arguments Syntax Y conv_p A B n_cpus conv_p A B n_cpus Y conv_p A B n_cpus Y mode_string and Y fftconv_p A B n_cpus Y wisdom_stringl fftconv_p A B n_cpus Y fftconv_p A B n_cpus wisdom_string fftconv_p A B n_cpus Y wisdom_string fftconv_p A B n_cpus Y mode_string fftconv_p A B n_cpus Y wisdom_string mode_string where A is an M x N matrix B is a K x N matrix or a K length vector If B is a vector then each column in A is convolved with B The parameter n_cpus is the number of threads to use which must be greater or equal to 1 and Y is the M K 1 x N output matrix The fftconv_p performs the convolutions in the frequency domain using the FFTW library 7 which is significantly faster than the time domain implementation conv_p for long vectors To use the fftconv p the FFTW3 lib must be available The win
50. re the first column contains the z coordinates the second the y coordinates and the third the z coordinates respectively NV is the number of observation points The single element transducers are by convention all centered at r 0 0 0 and the SIRs are computed relative to this center point The array functions uses a grid matrix G to define the positions 10 The DREAM ios 7 TRANSDUCER FUNCTION REFERENCE Transducer type DREAM function Strip transducer dreamline Rectangular transducer dreamrect Focused rectangular transducer dreamrect_f Circular transducer dreamcirc Focused circular transducer dreamcirc_f Spherical concave transducer focused dreamsphere_f Spherical convex transducer defocused dreamsphere_d Cylindrical concave transducer focused dreamcylind f Cylindrical convex transducer defocused dreamcylind d Array with rectangular elements dream_arr_rect Array with circular elements dream_arr_circ Array with cylindrical concave elements focused dream_arr_cylind_f Array with cylindrical convex elements defocused dream_arr_cylind_d Annular array dream_arr_annu Table 1 Overview of the DREAM toolbox transducer functions of the array elements see Section 7 4 The SIRs are therefore computed relative the positions given by the grid matrix for the arrays 7 1 2 Sampling Parameters The four element vector spar dx dy dt nt determines the spatial discretization and the
51. s the sampling interval T4 The max amplitude of the discrete SIR is therefore lower than then the max amplitude of the continuous SIR If the duration of the analytic SIR is longer than the sampling interval as for the 3 mm disc shown in Figure 4 b then the max amplitudes of the on axis sampled and analytic disc SIRs will be the same 5 3 The Discrete Representation DR Computational Concept As mentioned in previous in Section 5 1 the analytical spatial impulse responses are only available for a few simple transducer geometries Therefore for a transducer with an arbitrary geometry a numerical method must be used The numerical method used in this toolbox is based on the discrete representation DR method which is based on a discretization of the Rayleigh integral formula 1 In the DR method the radiating surface is divided into a set of small surface elements see illustration in Figure 5 and the surface integral in the Rayleigh formula is replaced by a summation The DR method facilitates computation of SIRs for non uniform excitation apodization of the aperture and arbitrary focusing laws since each surface element can be assigned a different normal velocity apdodization or time delay The DR computational concept can therefore be used for computing SIRs for an arbitrary transducer shape or array layout 1 2 A discrete SIR computed using the DR method can be found by first dividing the total transducer surface into a set of
52. s add addpath your_installation_dir to your matlab startup m file or use the menu in the MATLAB GUI 7 Copy the files pthreadGC2 d11 for gcc and 1ibfftw3 3 d11 to C WINDOWS System32 Method 2 Using the MSVC 2008 Express Edition 1 Download the DREAM Toolbox full source package and uncompress it SIf you are using an older version of Gnumex you may get an error that libmex def is missing happens for Matlab R2007a and above then the files libmx def libmat def and libmex def are missing in the MATLAB extern include di rectory They can however be created from the corresponding d11 files in MATLAB bin win32 directory with the pexports tool which can be found at http www emmestech com software pexports 0 43 download_pexports html Type pexports exe libmx dll gt libmx def etc in a cmd shell and copy the files to the MATLAB extern include directory This is not needed in newer versions of Gnumex which automatically build the def files if they are missing DREAM torrox 4 INSTALLATION 2 Start MATLAB and select compiler with mex setup if you have not already done so If Matlab cannot find the MSVC 2008 compiler then read this page http www mathworks com matlabcentral fileexchange loadFile do objectId 18508 Then after you have installed the bat files in their corresponding directories you need to set the env vari able MSSdk for the Windows SDK to for example C Program Files Microsoft SDKs Windows v6 1
53. s for the electro acoustical effects These two parts are then convolved to obtain a model for the total imaging system The impulse response method is very flexible since i by linearity the response from multi element transducers such as array transducers can be obtained be means of super position and ii arbitrary input signals can be treated by simply convolving the electro acoustical impulse response with the input The sources for Pthread win32 and fftw is now also included in the DREAM source package There are also scripts and patches for genrerating 64 bit versions of these libs using the MinGW w64 cross compiler tool chain on Linux see Appendix A and B 8The method described above for Matlab 2007x may work for Matlab 2008b or above too 19 DREAM 5 AN INTRODUCTION TO THE IMPULSE RESPONSE METHOD Transducer Figure 1 Illustration of a baffled transducer signal In this section we will present a short introduction to the impulse response method and in particular discuss how to use the method for discrete time modeling 5 1 The Baffled Piston Model and the Rayleigh integral The impulse response method is based on the assumption that the transducer can be treated as a baffled piston This assumption implies that we only need to consider the active area of the transducer when modeling the wave propagation That is if the source the transducer is located in the rigid plane often referred to as the rig
54. sducer The line or strip transducer has a length a and a small thickness equal to dy in s_par Syntax H dreamline Ro geom_par s_par delay m_par err_level Geometrical parameters geom_par la a mm length of the strip in x direction 7 3 2 Rectangular Transducer The size of the rectangular transducer is determined by a and b Syntax H dreamrect Ro geom_par s_par delay m_par err_level Geometrical parameters geom_par a b a mm x size b mm y size 7 3 3 Rectangular Focused Transducer The size of the rectangular focused transducer is determined by a and b and the focusing is described in Section 7 1 5 Syntax H dreamrect_f Ro geom_par s_par delay m_par foc_met focal err_level Geometrical parameters geom_par a b a mm x size b mm y size 99 The N DREAM ro 7 TRANSDUCER FUNCTION REFERENCE 7 3 4 Circular Transducer The size of the circular transducer is determined by the single parameter r Syntax h dreamcirc Ro geom_par s_par delay m_par err_level Geometrical parameters geom_par r r Radius of the transducer 7 3 5 Focused Circular Transducer The size of the focused circular transducer is determined by the parameter r and the focusing is described in Section 7 1 5 Syntax h dreamcirc_f Ro geom_par s_par delay m_par foc_met focal err_level Geometrical parameters geom_par r r Radius of the transducer
55. simulation 5 4 Lossy Media The computational procedure for an attenuation free medium implies a Dirac type Green s function 1 The discrete approach in the DREAM toolbox above is however also applicable to the problems char acterized by an arbitrarily shaped causal Green s function In such a case a Dirac function is simply replaced by a sampled version of this function This characteristic extends the field of applications and allows for example the computations for lossy media For such a case the free space Green s function 6 t rs ro c Am rs ro placed by its causal counterpart ga t rs ro related to the medium with absorption The solution for lossy media used in the DREAM toolbox for ga has the following frequency domain form 1 5 where rsis a point in the transducer surface and rois the observation point should be re 1 Tree ae Ga jw rs Fol er e s To wt 7 1 k th SP in 2 oof 8 C T AW a 7 0 95 and aola ggggsqor The time domain transfer function is then obtained by means of the inverse Fourier transform where Ja t rs rol P Gale rs Tol 9 TF DREAM rono 6 A QUICK START TO DREAM SIMULATIONS In the DREAM toolbox this computation is performed by a discrete Fourier transform for each surface element dxxdy An illustration of the effects due to lossy media for an attenuation of coefficient a of 1
56. temporal sampling properties The spatial discretization of the transducer surface is given by dxxdy small values of dx and dy results in a finer mesh and a higher numerical accuracy compared to larger ones The temporal sampling interval At or T is given by dt and the length of the SIR vector is determined by nt If nt is chosen too low so that any non zero component of the SIR is not within the time window defined by delay dt nt 1 delay an error message will be printed See Section 7 1 3 for a description of the delay parameter and Section 7 1 6 for a description of the error handling in the DREAM toolbox dx Spatial discretization size in x direction mm dy Spatial discretization size in y direction mm dt Temporal discretization size us Ts At 1 sampling freq nt Length of spatial impulse response vector 7 1 3 The Delay Parameter The starting point of the SIR vector s is given by the delay parameter delay js The delay parameter can either be a scalar then all SIRs will have the same starting point or it can be a vector with a length that must be equal to the number of observation points In the latter case each observation point has a SIR with a different starting point 7 1 4 Material Parameters The material parameters are given by the three element vector m_par v cp alfa v Normal velocity of the transducer surface m s gA The DREAM oro 7 TRANSDUCER FUNCTION REFERENCE cp Sound velocity of th
57. tion 10 3 and the output parameter Y is an M K 1 x N matrix A typical usage is Compute a new fftw wisdom string tmp wisdom_str fftconv_p A 1 1 B 1 n_cpus for i 1 N Do some stuff here Y sum_fftconv_p A B n_cpus wisdom_str end where the overhead of calling fftw plan functions is now avoided inside the for loop 10 4 Parallel Matrix Copy The impulse response matrices can often become rather large and the time taken to copy data between matrices can therefore be considerable The DREAM Toolbox comes with a threaded function copy_p to speed up data copy In place threaded copy of data into a matrix copy_p B row_idx col_idx A n_cpus Input parameters B Pre allocated Output matrix of size gt r2 r1 x c2 c1 row_idx ri r2 Two element vector defining rows in B where the data is copied col_idx c1 c2 Two element vector defining columns in B where the data is copied B Input matrix of size r2 r1 x c2 c1 n_cpus Number of threads to use n_cpus must be greater or equal to 1 10 5 The Speed of Sound in Water The SIRs are a function of the sound speed in the propagation medium which often is water The DREAM toolbox comes with a function h20_soundspeed based on a method by V A Del Grosso 8 to facilitate computation of the water sound speed as function of temperature pressure and salinity cp h2o_soundspeed T P unit S Input parameters 29 DREAM circ 1
58. uild the DREAM Octave oct files for 64 bit Windows Currently there is no support for building 64 bit oct files since there is no 64 bit version of Octave for Windows available yet 4 5 8 Compile with FFTW support for the Attenuation Code The attenuation code in the DREAM Toolbox uses FFTs extensively To speed up the FFT computations by 10 to 50 one can compile The DREAM Toolbox with FFTW support for the attenuation code To do this you need to compile all functions with the flag DUSE_FFTW and link with 1fftw3 This can be accomplished by changing ATT_FFTW FFW_LIB to ATT_FFTW DUSE_FFTW FFW_LIB lfftw3 in the file Make default before compiling the toolbox if you are using Method 3 described in Section 4 5 1 the build_dream sh uses fftw by default 5 An Introduction to The Impulse Response Method HE impulse response method is an approach based on linear systems theory to model acoustic fields from ultrasonic transducers the method was introduced by Tupholme and Stepanishen in the late 60 s early 70 s 3 4 The impulse response method is based on linear acoustics and can be used to model acoustic fields and double path responses for both single transducer setups and for array imaging The idea is to divide the imaging system in two parts the first one accounts for acoustical wave propagation effects i e the diffraction effects from the transducer surface to the observation point and the second one account
59. ulse Responses o e o e 15 5 3 The Discrete Representation DR Computational Concept 16 Ga Loss Media cc ey hha ae ee EA AS SMR Me Gea ob Oe Ea 17 6 A Quick Start to DREAM Simulations 18 7 Transducer Function Reference 19 7 1 Input Parameters Common to all Transducer Functions s o aoo 19 7 1 1 Observation Point s Parameter o eee ee eee 19 Falo Sampling Porameler s coc es a RH SRA oe Bok Oe Ew 20 TLS Tie Delos Paraiieter oo eeu EE a Shar e BES SE GS 20 TLA Material Parameters coce so cor ca ee ee RE ee a ee 8 20 Gio Focusing parameters c cae samasa aa adaa OR GR A D 21 LIO Eror Handing oeoo e a ba a oo ee ee e ee eS ee a 21 7 2 Output Parameters Common to all Transducer Functions 21 7 2 1 TheSIR Output Argument 2 2 ee ER RED 21 8 9 7 2 2 The Error Output Argument occ os rss ss to Single Element Transducers ss o o lt oo o ye ye Tal Line strip Transducer socorrer a A e RA Tal Retangular Transdicer s ci iro 6 eR a e Re oo Rectangular Focused Transducer s coros we ee Gee ee ee E 134 Liecular Transducer oa coros ke ee Pe A a ee ee eS Tao Focused Circular Transducer cocos Pee RE Ee DA 1306 Spherical Concave Transduc r o o coc s mie OR ee ae oe ee a a 73 7 Spherical Convex Transducer 2 saaa eee aa r edk iei 7 3 8 Cylindrical Concave Transducer e 7 3 9 Cylindrical Convex Transdu
60. used architecture and the attenuation code is build without fftw support see Section 4 5 8 This will also only build the mex files not the oct files 4Note this will not build the documentation 5The build of the documentation has only been tested on Linux based systems DREAM roro 4 INSTALLATION Install fftw if it is not already installed Start MATLAB and select compiler gcc is recommended with mex setup if you have not already done so Remove the ansi flag from your matlab R200Xx mexopts sh file the DREAM sources contain C style comments and they will not compile with ansi Run the m script build mexfiles_unix Copy the files in the gui and help m files directories to your DREAM install directory Add your DREAM install directory to the MATLAB path That is add addpath your_installation_dir to your matlab startup m file Method 2 Using the build_dream sh bash script The bash script build_dream sh will probe the machine for cpu architecture 32 or 64 bits and then use a pre defined set of compiler flags for the machine currently only x86 is supported This script will both build the mex oct interfaces and the documentation for DREAM It is assumed that MATLAB is installed in usr local matlab If you have installed MATLAB somewhere else then you can create a symbolic link to the usr local matlab dir Usage build_dream sh Then add your DREAM install directory to the MATLAB O
61. used instead as described in Section 4 5 4 To use MSVC one therefore needs an older MSVC build binary of Octave or one has to build Octave and all its dependencies using the MSVC compiler and then follow the procedure below il 2 10 11 Download the DREAM Toolbox pkg source package and uncompress it Download the MSVC version of Octave build with the Microsoft Visual C 2008 Express Edition compiler Install Octave in C Qctave do not install in C Program FileslOctave since the mkoctfile script that is used to compile the C code in the DREAM toolbox do work well with white spaces in the path Install Microsoft Visual C 2008 Express Edition Get the fftw3 h file for version 3 2 2 from http www fftw org or from DREAM web page and copy it to C Octave include you don t need to install the fftw3 d11 file since it is already included in the MSVC version of Octave Get the phread h shed h and semaphore h files from http sourceware org pthreads win32 version 2 8 0 or from the DREAM web page and copy them to C Qctave include Get the phreadGC2 1ib file from http sourceware org pthreads win32 or from the DREAM web page copy it to C Octave lib and rename it to phread lib the Unix style Makefile which is used to build the toolbox expects this name of the lib file Create a new bat file and add the lines echo off call C Program Files Microsoft Visual Studio 9 0 VC vcvarsal
62. y is computed which is represented with a 1 at the corresponding index The das function is for single transducers and the das_arr function is for arrays The input parame ters D err das Ro s_par delay m_par err_level D err das_arr Ro G s_par delay m_par foc_met focal steer_met steer_par apod_met apod win_par err_level are similar to the ones used in the transducer functions previously described 24 DREAM roro 11 SIGNAL PROCESSING EXAMPLES 11 4 Model Based Ultrasonic Array Imaging In this section a short introduction to model based ultrasonic imaging is presented Model based ultrasonic array imaging 17 19 is different from delay and sum imaging in the sense that is based on optimal information processing whereas delay and sum imaging is based on geometrical focusing The idea is to use a linear model taking into account the diffraction effects associated with each transmitter receiver the electrical characteristics for each transmitter receiver as well as the used input signal s and then estimate the parameters the scattering strengths of the model based on both data and prior information The DREAM toolbox can be used in this process for computing the SIRs for the model which can then be convolved with measured electrical impulse responses to obtain a model for a real measurement setup or using only simulated impulse responses to evaluate different array designs for example To obtain a linear mode

User Manual for the DREAM Toolbox Version 2.1.3 An ultrasound

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