Delay and Sum beamforming (ultrasound beamforming)
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Hi everyone,
How do I convert the discrete samples in to distance in order to find the Rx_delay of this basic beamformer?
Here is my code. I would appreciated any suggestions.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%
% This function performs DAS beamforming for the RF data reveiced
% from a plane wave transmission without beamsteering (0 degrees).
%
% For each pixel (xj,zj), distances are calculated by summing the
% distance from the transmiter to the point and distance from point
% to the receiving element as follows:
% total distance = TX delay path + RX delay path
% TX_delay = zj
% RX_delay = sqrt(zj^2 + (xj-x)^2)
%
%
% "RF_data128" contains received signal from each channel
% "z_start" is the imaging depth starting point
% "z_stop" is the imaging depth ending point
% "image_width" is the required imaging width
% "delta_x" is the lateral step size between each lines of the image
% "pitch" is the distance between the centres of adjacent elements
% "c" is the sound speed
% "fs" is the sampling frequency
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [Beamformed_DATA, z_axis, x_axis] = Basic_Beamformer(RF_data128, z_start, z_stop, image_width, delta_x, pitch, c, fs)
tic
% Receive data parameters
delta_t = 1/fs; % Sampling interval (time)
delta_d = c * delta_t; % Sampling interval (distance)
receive_depth = size(RF_data128,1); % Receive samples (depth)
N_elements = size(RF_data128,2); % Number of receive channels = Number of elements
% Image data parameters
delta_z = delta_d/2;
x_axis = -image_width/2 : delta_x : image_width/2; % Define image x-axis (lateral)
z_axis = z_start: delta_z : z_stop; % Define image z-axis (axial)
Beamformed_DATA = zeros(length(z_axis), length(x_axis)); % Allocate memeory for the Beamformed Data
% Calculate the diagonal length as the maximum image dimension (in samples)
max_dimension = round(sqrt(image_width^2 + z_stop^2)/(delta_z));
% Zero padding according to the maximum image dimension
RF_data128_padded = [RF_data128; zeros(max_dimension-receive_depth, N_elements)];
% Delay calculations and Beamforming
for channel = 1 : N_elements % Beamform every channel
channel_location = channel*pitch;
for zj = 1 : length(z_axis) % Calculate the beamformed data for each pixel (depth)
TX_delay = zj*delta_z; % Distance from the transmitter to the points
for xj = 1 : length(x_axis) % Calculate the beamformed data for each pixel (lateral)
RX_delay =sqrt(zj^2 + (xj-x)^2)*delta_x ; % Distance from the point to the receiver
RF_address = round((TX_delay + RX_delay)/delta_d);
Beamformed_DATA(zj, xj) = Beamformed_DATA(zj, xj) + RF_data128_padded(RF_address, channel);
end
end
end
toc
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