bft_user_guide.tex.bak

超声仿真软件

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%%tth:\subsection*{bft\_init}
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\funlnk{bft_init}

Initialize the BeamForming Toolbox. This command must be
    executed first in order to set some parameters and allocate the 
    the necessary memory
    
\begin{tabular}[t]{lp{14cm}}  
USAGE:& {\tt bft\_init}\\
INPUT:& None \\
OUTPUT:& None
\end{tabular}


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\headline{bft\_linear\_array}
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%%tth:\subsection*{bft\_linear\_array}
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\funlnk{bft_linear_array}


 Create a linear array aperture.
 
\begin{tabular}[t]{lp{14cm}}  
 USAGE: & {\tt xdc = bft\_linear\_array(no\_elements, width, kerf)} \\
   &     {\tt xdc = bft\_linear\_array(no\_elements, pitch)} \\
 
 INPUT:& \begin{tabular}[t]{lp{11cm}}  
          {\sl no\_elements} & Number of elelements in the array \\
          {\sl pitch} & Distance between the centers of two elements [m] \\
          {\sl width} & Width in x-direction                         [m]\\
          {\sl kerf}  & Distance between two elements                [m] 
         \end{tabular} \\
          
        & The function assumes that {\sl kerf + width = pitch} \\
 OUTPUT:& {\sl xdc} - Pointer to the allocated aperture.
\end{tabular}

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\headline{bft\_no\_lines}
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%%tth:\subsection*{bft\_no\_lines}
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\funlnk{bft_no_lines}

Set the number of lines that will be beamformed in parallel.
  After calling \hyperlink{bft_init}{bft\_init}, the number of lines 
that are beamformed in   parallel is 1. If the user wants to beamform
a whole image in one  command, he/she must set the number of lines,
and then specify the focal zones for each of the lines.

\begin{tabular}[t]{lp{14cm}}  
 
 USAGE: & {\tt bft\_no\_lines(no\_lines)}\\
 INPUT:& {\sl no\_lines}  ~~Number of lines beamformed in parallel \\
 OUTPUT: & None
\end{tabular}


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\headline{bft\_param}
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%%tth:\subsection*{bft\_param}
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\funlnk{bft_param}

Set a paramater of the BeamForming Toolbox

\begin{tabular}[t]{lp{14cm}}  

 USAGE: & {\tt bft\_param(name, value)}\\
 
 INPUT: & \begin{tabular}[t]{lp{11cm}}  
          {\sl name} & Name of  the parameter (string). Currently supported:\\
        &  \begin{tabular}[t]{c|c|c|c}
           \hline 
            name &        Meaning       & Default value &  Unit \\
            \hline 
                  'c' & Speed of sound.       & 1540         &  m/s \\
                  'fs'& Sampling frequency    & 40,000,000   &  Hz \\
            \hline       
          \end{tabular} \\\\
         
          {\sl value} & New value for the parameter. Must be scalar. 
          \end{tabular} \\
 OUTPUT: & None
\end{tabular}


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\headline{bft\_sub\_image}
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%%tth:\subsection*{bft\_sub\_image}
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\funlnk{bft_sub_image}

Subtract one low-res image from  high-res one.

\begin{tabular}[t]{lp{14cm}}  
 
 USAGE: & {\tt [hi\_res] = bft\_sub\_image(hi\_res, lo\_res, element, start\_time)} \\
 
 INPUT:& \begin{tabular}[t]{lp{11cm}}  
          {\sl hi\_res}  & High resolution RF image. One column per scan line.\\
          {\sl lo\_res}  & Low resolution RF image. One column per scan line.\\
          {\sl element} & Number of element, used to acquire the low resolution
                    image. \\
          {\sl start\_time}    & Arrival time of the first sample of the RF lines.
          \end{tabular} \\
 OUTPUT:& hi\_res - The high resolution image.
\end{tabular}

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\headline{bft\_sum\_apodization}
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%%tth:\subsection*{bft\_sum\_apodization}
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\funlnk{bft_sum_apodization}

Create a summation apodization time line.
    This function is used in the case that the individual low
    resolution images must be weighted during the summation

\begin{tabular}[t]{lp{14cm}}  
 
  USAGE: & {\tt  bft\_sum\_apodization(xdc, times, values, line\_no)} \\
 
  INPUT: & \begin{tabular}[t]{lp{14cm}}  
          {\sl xdc} & Pointer to a transducer aperture.\\
          {\sl times} & Timea after which the associated apodization is valid.\\
          {\sl values} & Apodization values. Matrix with one row for each
                   time value and a number of columns equal to the 
                   number of physical elements in the aperture. \\
          {\sl line\_no} & Number of line. If skipped, {\sl line\_no} is assumed
                    to be equal to '1'.
         \end{tabular}\\
  OUTPUT: & None         
\end{tabular}


\headline{bft\_sum\_images}
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%%tth:\subsection*{bft\_sum\_images}
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\funlnk{bft_sum_images}

 Sum 2 low resolution images in 1 high resolution.

\begin{tabular}[t]{lp{14cm}}  
 
 USAGE  : {\tt [hi\_res] = bft\_sum\_images(image1, ele1, image2, ele2, time) }\\
 
 INPUT  : \begin{tabular}[t]{lp{141cm}}  
          {\sl image1} & Matrix with the RF data for the image. The number
                   of columns corresponds to the number of lines \\
          {\sl ele1}   & Number of emitting element used to obtain the image.\\ 
          {\sl image2} & Matrix with the RF data for the image. The number
                   of columns corresponding to the number of lines \\
          {\sl ele2}   & Number of emitting element used to obtain the image.\\
          {\sl time}   &  The arrival time of the first samples. The two images
                    must be aligned in time 
          \end{tabular}
 OUTPUT : hi\_res - Higher resolution image
\end{tabular}

\headline{bft\_transducer}
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%%tth:\subsection*{bft\_transducer}
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\funlnk{bft_transducer}
 
 Create a new transducer definition. 
    The transducer definition is necessary for the calculation of 
    the delays.

\begin{tabular}[t]{lp{14cm}}  
 
 USAGE: &  {\tt xdc = bft\_transducer(centers)}\\
 
 INPUT: & \begin{tabular}[t]{lp{11cm}}  
            {\sl centers} & Matrix with the coordinates of the centers of 
                   the elements. It has 3 columns (x,y,z) and a
                   number of rows equal to the number of elements.
                   The coordinates are specified in [m]
         \end{tabular}\\ 
 OUTPUT: & \begin{tabular}[t]{lp{11cm}}  
          xdc & Pointer to the memory location with the transducer 
               definition. Do not alter this value !!!
          \end{tabular}
\end{tabular}

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\chapter{Examples}
\label{chap_examples}
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\section{Using Field II simulations}

\headline{Phased array B-mode image}
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%%tth:\subsection*{phased array B-mode image}
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\funlnk{phased_bmode}

{\footnotesize
\begin{verbatim}
%PHASED_IMAGE Create phased array B-mode image with BFT.
%    This script creates a B-mode PSF line by line. Each line is 
%    calculated using CALC_SCAT and CALC_SCAT_MULTY. The rf_data
%    from CALC_SCAT_MULTI is passed to  the beamforming toolbox,
%    and in the end the results are compared.
%
%    The function calls XDC_FOCUS, and BFT_FOCUS in order to set the
%    the delays. 

% VERSION 1.0, 29 Feb. 2000, Svetoslav Nikolov

f0 = 4e6;              %  Central frequency                       [Hz]
fs = 100e6;            %  Sampling frequency                      [Hz]
c = 1540;              %  Speed of sound                          [m/s]
no_elements = 64;      %  Number of elements in the transducer

lambda = c / f0;       % Wavelength                               [m]
pitch = lambda / 2;    % Pitch - center-to-center                 [m]
width = .95*pitch;     % Width of the element                     [m]
kerf = pitch - width;  % Inter-element spacing                    [m]
height = 10/1000;      % Size in the Y direction                  [m]
 
 
%  Define the impulse response of the transducer
impulse_response = sin(2*pi*f0*(0:1/fs:2/f0));
impulse_response = impulse_response.*hanning(length(impulse_response))';
excitation = impulse_response;

%  Define the phantom

pht_pos = [0 0 20;
           0 0 30;
           0 0 40;
           0 0 50;
           0 0 60;
           0 0 70;
           0 0 80;
           0 0 90;
           ] / 1000;         %  The position of the phantom
pht_amp = 20*ones(8,1);      %  The amplitude of the back-scatter



%  Define the focus 
focus_r = [20;30;40;50;60;70;80;90] / 1000;
T = (focus_r-5/1000)/c *2;


%  Initialize the program
field_init(0);
bft_init;


%  Set some paramters
set_field('c', c);
bft_param('c', c);

set_field('fs', fs);
bft_param('fs', fs);



% Create some apertures.

xmt = xdc_linear_array(no_elements,width,height,kerf,1,1,[0 0 0]);
rcv = xdc_linear_array(no_elements,width,height,kerf,1,1,[0 0 0]);

xdc = bft_linear_array(no_elements, width, kerf);


% Set the impulse responses
xdc_impulse(rcv, impulse_response);
xdc_impulse(xmt, impulse_response);

xdc_excitation(xmt, excitation);



%  Define and create the image
sector = 30 * pi / 180;
no_lines = 32;
d_theta = sector / (no_lines-1);
theta = -(no_lines-1) / 2 * d_theta;

Rmax = max(sqrt(pht_pos(:,1).^2 + pht_pos(:,2).^2  + pht_pos(:,3).^2)) + 15/1000;

no_rf_samples = ceil(2*Rmax/c * fs);
rf_line = zeros(no_rf_samples, 1);
bf_line = zeros(no_rf_samples, 1);

env_line = zeros(no_rf_samples, no_lines);
env_bf =  zeros(no_rf_samples, no_lines);


xmt_r = (max(focus_r) + min(focus_r) )/2;

for i = 1 : no_lines
  rf_line(:) = 0;  
  disp(['Line no ' num2str(i)])
  
  focus = [sin(theta)*focus_r, zeros(length(focus_r),1), cos(theta)*focus_r];
  xmt_f = [sin(theta)*xmt_r, zeros(length(xmt_r),1), cos(theta)*xmt_r];
  xdc_center_focus(xmt,[0 0 0])
  xdc_center_focus(rcv,[0 0 0])
  bft_center_focus([0 0 0]);
  
  xdc_focus(xmt, 0, xmt_f);
  xdc_focus(rcv, T, focus);
  bft_focus(xdc, T, focus);
  
  %  Beamform with Field II
  [rf_temp, t(i)] = calc_scat(xmt,rcv, pht_pos, pht_amp);
  
  %  Beamform with BFT
  xdc_focus_times(rcv, 0, zeros(1,no_elements));
  [rf_data, start_t] = calc_scat_multi(xmt,rcv, pht_pos, pht_amp);
  rf_data = [zeros(300,no_elements); rf_data; zeros(300,no_elements)];

  start_t = start_t - 300  / fs;
  bf_temp = bft_beamform(start_t, rf_data);
  
  start_sample = t(i)*fs; no_temp_samples = length(rf_temp);
  
  rf_line(start_sample:start_sample+no_temp_samples-1) = rf_temp(1:no_temp_samples);
  env_line(:,i) = abs(hilbert(rf_line(:)));

  start_sample = floor(start_t*fs); no_temp_samples = length(bf_temp);
  bf_line(start_sample:start_sample+no_temp_samples-1) = bf_temp(1:no_temp_samples);
  env_bf(:,i) = abs(hilbert(bf_line(:)));
  theta = theta + d_theta;

end

%  Release the allocated memory

field_end
bft_end

env_line = env_line / max(max(abs(env_line)));
env_bf = env_bf / max(max(abs(env_bf)));

figure;
subplot(1,2,1)
imagesc([-sector/2 sector/2]*180/pi,[0 Rmax]*1000,20*log10(env_line + 0.001))
axis('image')
xlabel('Angle [deg]');
ylabel('Axial distance [mm]')
title('Beamformed by Field II ');