STAI_L11_speckle

Computation of a STAI dataset with Field II and beamforming with USTB
basic constants
field II initialisation
Transducer definition L11-4v, 128-element linear array transducer
pulse definition
aperture objects
phantom of speckle
output data
Compute STA signals
SEQUENCE GENERATION
CHANNEL DATA
SCAN
PIPELINE
Save UFF dataset

Computation of a STAI dataset with Field II and beamforming with USTB

This example shows how to load the data from a Field II simulation into USTB objects, and then beamformt it with the USTB routines. This example uses the L11-4v 128 element Verasonics Transducer The Field II simulation program (field-ii.dk) should be in MATLAB's path.

authors: Alfonso Rodriguez-Molares alfonso.r.molares@ntnu.no Ole Marius Hoel Rindal olemarius@olemarius.net

Last updated: 07.08.2017

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 L11-4v, 128-element linear array transducer

probe = uff.linear_array();
f0                      = 5.1333e+06;      % Transducer center frequency [Hz]
lambda                  = c0/f0;           % Wavelength [m]
probe.element_height    = 5e-3;            % Height of element [m]
probe.pitch             = 0.300e-3;        % probe.pitch [m]
kerf                    = 0.03e-03;        % gap between elements [m]
probe.element_width     = probe.pitch-kerf;% Width of element [m]
lens_el                 = 20e-3;           % position of the elevation focus
probe.N                 = 128;             % Number of elements
pulse_duration          = 2.5;             % pulse duration [cycles]

pulse definition

pulse = uff.pulse();
pulse.center_frequency = f0;
pulse.fractional_bandwidth = 0.65;        % probe bandwidth [1]
t0 = (-1/pulse.fractional_bandwidth/f0): dt : (1/pulse.fractional_bandwidth/f0);
impulse_response = gauspuls(t0, f0, pulse.fractional_bandwidth);
impulse_response = impulse_response-mean(impulse_response); % To get rid of DC

te = (-pulse_duration/2/f0): dt : (pulse_duration/2/f0);
excitation = square(2*pi*f0*te+pi/2);
one_way_ir = conv(impulse_response,excitation);
two_way_ir = conv(one_way_ir,impulse_response);
lag = length(two_way_ir)/2+1;

% show the pulse to check that the lag estimation is on place (and that the pulse is symmetric)
figure;
plot((0:(length(two_way_ir)-1))*dt -lag*dt,two_way_ir); hold on; grid on; axis tight
plot((0:(length(two_way_ir)-1))*dt -lag*dt,abs(hilbert(two_way_ir)),'r')
plot([0 0],[min(two_way_ir) max(two_way_ir)],'g');
legend('2-ways pulse','Envelope','Estimated lag');
title('2-ways impulse response Field II');

aperture objects

definition of the mesh geometry

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]);

% setting excitation, impulse response and baffle
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 of speckle

number_of_scatterers = 100;
xxp_speckle=random('unif',-5e-3,5e-3,number_of_scatterers,1);
zzp_speckle=random('unif',15e-3,20e-3,number_of_scatterers,1);
sca = [xxp_speckle zeros(length(xxp_speckle),1) zzp_speckle];  % list with the scatterers coordinates [m]
amp=randn(length(sca));                   % list with the scatterers amplitudes

output data

cropat=round(1.1*2*sqrt((max(sca(:,1))-min(probe.x))^2+max(sca(:,3))^2)/c0/dt);   % maximum time sample, samples after this will be dumped
STA=zeros(cropat,probe.N,probe.N);    % impulse response channel data

Compute STA signals

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, sca, amp);

    % 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

end
close(wb);

Index exceeds the number of array elements (1).

Error in STAI_L11_speckle (line 88)
disp('Field II: Computing STA dataset');

CHANNEL DATA

channel_data = uff.channel_data();
channel_data.sampling_frequency = fs;
channel_data.sound_speed = c0;
channel_data.initial_time = 0;
channel_data.pulse = pulse;
channel_data.probe = probe;
channel_data.sequence = seq;
channel_data.data = STA*10^29;

SCAN

scan=uff.linear_scan('x_axis',linspace(-5e-3,5e-3,256).', 'z_axis', linspace(15e-3,20e-3,256).');

PIPELINE

pipe=pipeline();
pipe.channel_data=channel_data;
pipe.scan=scan;

% Delay and sum on receive, then coherent compounding
b_data=pipe.go({midprocess.das() postprocess.coherent_compounding()});
% Display image
b_data.plot()

envelope = abs(b_data.data);
envelope = envelope./max(envelope(:));
m = mean(envelope(:));
s = std(envelope(:));

snr_calculated_das = m/s
snr_theoretical = (pi/(4-pi))^(1/2)
b = s/(sqrt((4-pi)/2)); %Scale parameter

% Estimate PDF
x_axis = linspace(0,1,200);
[n,xout] = hist(envelope(:),x_axis);
delta_x = xout(2)-xout(1);
n = n/sum(n)/delta_x;

% Theoretical Raileigh PDF
theoretical_pdf = (x_axis./b^2).*exp(-x_axis.^2/(2.*b^2));

% Plot
color=[0.25 1 0.75]
figure(1);clf;
plot(xout,n,'LineWidth',2,'Color','r','DisplayName','Estimated PDF');hold on;
plot(x_axis,theoretical_pdf,'--','Color',color,'LineWidth',2,'DisplayName','Rayleigh Theoretical PDF');
title('PDF of envelope');
xlabel('Normalized amplitude');
ylabel('Probability')
legend('show');

Save UFF dataset

filename=[ustb_path(),'/data/FieldII_speckle_simulation_v2.uff'];
channel_data.write(filename,'channel_data');
b_data.write(filename,'beamformed_data');

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