A comparison of axial and lateral PSF profiles of Field II against USTB's Fresnel simulator.
_by Alfonso Rodriguez-Molares alfonso.r.molares@ntnu.no, Ole Marius Hoel
Contents
Close old plots
close all;
Basic Constants
c0=1540; % Speed of sound [m/s] fs=100e6; % Sampling frequency [Hz] dt=1/fs; % Sampling step [s]
field II initialisation
field_init(0); set_field('c',c0); % Speed of sound [m/s] set_field('fs',fs); % Sampling frequency [Hz] set_field('use_rectangles',1); % use rectangular elements
*------------------------------------------------------------*
* *
* F I E L D I I *
* *
* Simulator for ultrasound systems *
* *
* Copyright by Joergen Arendt Jensen *
* Version 3.30, April 5, 2021 (Matlab 2021a version) *
* Web-site: field-ii.dk *
* *
* This is citationware. Note the terms and conditions *
* for use on the web-site at: *
* field-ii.dk/?copyright.html *
* It is illegal to use this program, if the rules in the *
* copyright statement is not followed. *
*------------------------------------------------------------*
Warning: Remember to set all pulses in apertures for the new sampling frequency
Transducer definition L9-4/38 Ultrasonix, 128-element linear array transducer
probe = uff.linear_array(); f0 =5e6; % Transducer center frequency [Hz] lambda =c0/f0; % Wavelength [m] probe.element_height =6e-3; % Height of element [m] probe.pitch =0.3048e-3; % probe.pitch [m] kerf =0.035e-3; % gap between elements [m] probe.element_width =probe.pitch-kerf;% Width of element [m] lens_el =19e-3; % position of the elevation focus probe.N =128; % Number of elements
Pulse definition
pulse = uff.pulse(); pulse.center_frequency = f0; pulse.fractional_bandwidth = 0.6; % probe bandwidth [1] t0=(-1.0/pulse.fractional_bandwidth /f0): dt : (1.0/pulse.fractional_bandwidth /f0); excitation=1; impulse_response=gauspuls(t0, f0, pulse.fractional_bandwidth ); two_ways_ir= conv(conv(impulse_response,impulse_response),excitation)./norm(impulse_response).^2; if mod(length(impulse_response),2) lag=(length(two_ways_ir)-1)/2; else lag=(length(two_ways_ir))/2; end fig_handle=figure; plot(((0:(length(two_ways_ir)-1))*dt -lag*dt)*1e6,two_ways_ir); hold on; grid on; axis tight plot(((0:(length(two_ways_ir)-1))*dt -lag*dt)*1e6,abs(hilbert(two_ways_ir)),'r') plot([0 0],[min(two_ways_ir) max(two_ways_ir)],'g'); legend('2-ways pulse','Envelope','Estimated lag'); title('2-ways impulse response Field II'); pulse.plot(fig_handle,'','--');
Aperture Objects
noSubAz=round(probe.element_width/(lambda/8)); % number of subelements in the azimuth direction noSubEl=round(probe.element_height/(lambda/8)); % number of subelements in the elevation direction Th = xdc_linear_array (probe.N, probe.element_width, probe.element_height, kerf, noSubAz, noSubEl, [0 0 Inf]); Rh = xdc_linear_array (probe.N, probe.element_width, probe.element_height, kerf, noSubAz, noSubEl, [0 0 Inf]);
Excitation
xdc_excitation (Th, excitation); xdc_impulse (Th, impulse_response); xdc_baffle(Th, 0); xdc_center_focus(Th,[0 0 0]); xdc_impulse (Rh, impulse_response); xdc_baffle(Rh, 0); xdc_center_focus(Rh,[0 0 0]);
Phantom
pha=uff.phantom(); pha.sound_speed=1540; % speed of sound [m/s] pha.points=[0, 0, 20e-3, 1]; % point scatterer position [m] fig_handle=pha.plot(); cropat=round(1.1*2*sqrt((max(pha.points(:,1))-min(probe.x))^2+max(pha.points(:,3))^2)/c0/dt); % maximum time sample, samples after this will be dumped
Output data
t_out=0:dt:((cropat-1)*dt); % output time vector STA=zeros(cropat,probe.N,probe.N); % impulse response channel data
Compute STA signals using Field II
disp('Field II: Computing STA dataset'); wb = waitbar(0, 'Field II: Computing STA dataset'); for n=1:probe.N waitbar(n/probe.N, wb); % transmit aperture xdc_apodization(Th, 0, [zeros(1,n-1) 1 zeros(1,probe.N-n)]); xdc_focus_times(Th, 0, zeros(1,probe.N)); % receive aperture xdc_apodization(Rh, 0, ones(1,probe.N)); xdc_focus_times(Rh, 0, zeros(1,probe.N)); % do calculation [v,t]=calc_scat_multi(Th, Rh, pha.points(1:3), pha.points(4)); % build the dataset STA(1:size(v,1),:,n)=v; % Sequence generation seq(n)=uff.wave(); seq(n).probe=probe; seq(n).source.xyz=[probe.x(n) probe.y(n) probe.z(n)]; seq(n).sound_speed=c0; seq(n).delay = probe.r(n)/c0 - lag*dt + t; % t0 and center of pulse compensation seq(n).apodization = uff.apodization(); seq(n).apodization.window=uff.window.sta; end close(wb);
Index exceeds the number of array elements (1).
Error in STAI_PSF (line 88)
disp('Field II: Computing STA dataset');
Channel Data
channel_data_field_ii = uff.channel_data(); channel_data_field_ii.sampling_frequency = fs; channel_data_field_ii.sound_speed = c0; channel_data_field_ii.initial_time = 0; channel_data_field_ii.pulse = pulse; channel_data_field_ii.probe = probe; channel_data_field_ii.sequence = seq; channel_data_field_ii.data = STA;
Scan
sca=uff.linear_scan('x_axis',linspace(-20e-3,20e-3,256).','z_axis', linspace(1e-3,40e-3,256).');
Pipeline
das = midprocess.das(); das.dimension = dimension.both; das.channel_data=channel_data_field_ii; das.scan=sca; das.transmit_apodization.window=uff.window.hanning; das.transmit_apodization.f_number=1.7; %das.transmit_apodization.tilt=20*pi/180; %das.transmit_apodization.plot() das.receive_apodization.window=uff.window.hanning; das.receive_apodization.f_number=1.7; das.receive_apodization.tilt=20*pi/180; %das.receive_apodization.probe = probe; %das.receive_apodization.focus = sca; %das.receive_apodization.plot() b_data_field_ii =das.go(); b_data_field_ii.plot([],'Field II Simulation',70) %das.receive_apodization.plot()