Fourier Based Field-shift for MRI源码程序 - matlab算法设计

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标题：Fourier Based Field-shift for MRI源码程序
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所属分类: 算法设计资源类型：文件大小: 4.75 KB 上传时间: 2016-01-25 19:41:57 下载次数: 5 资源积分：1分提供者: xiaopeng2 Fourier Based Field-shift for MRI源码程序

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Fourier Based Field-shift for MRI源码程序，程序员在编程的过程中可以参考学习使用，希望对IT程序员有用，此源码程序简单易懂、方便阅读，有很好的学习价值！

%% Fourier Based Field-shift Calculation for MRI

% A test file to demonstrate the feasibility of low resolution

% aliasing subtraction.

%% Written 06-07-2012 by Job Bouwman (jgbouwman@hotmail.com)

% Updated 14-06-13

clear all; close all; clc;

%% creating a numerical phantom:

% - an eccentric sphere (radius of 97.3)

% - with tissue-like susceptibility (dChi = - 9 ppm)

% - within an FOV of (256 x 256 x 256)

N = 192;

radius = round(0.38*N);

dChi = -9e-6;

voxelSize = [1 1 1];

M = round(0.4*N);

Nx = N; Ny = N; Nz = N;

Mx = M; My = M; Mz = M;

FOV = [Ny Nx Nz].*voxelSize;

X_dev = zeros(Ny, Nx, Nz);

X_dev(My,Mx,Mz) = 1;

X_dev = bwdist(X_dev);

X_dev(X_dev<=radius) = dChi;

X_dev(X_dev>radius) = 0;

%% The kernel (Gk):

kxSeries = (-Nx/2:Nx/2-1)/FOV(2);

kySeries = (-Ny/2:Ny/2-1)/FOV(1);

kzSeries = (-Nz/2:Nz/2-1)/FOV(3);

[kx, ky, kz] = meshgrid(kxSeries,kySeries,kzSeries);

k2 = kx.^2 + ky.^2 + kz.^2;

k2(k2==0) = eps;

Gk = 1/3 - kz.^2 ./ k2;

Gk(k2==eps) = 0;

Gk = ifftshift(Gk);

%% Field shift calculations:

% without zero-padding the result would be:

B_dev_aliased = ifftn(fftn(X_dev).*Gk);

% with virtual zero-padding the result is:

B_dev_cleared = calculateFieldShift(X_dev, voxelSize);

% thus the aliasing removed is:

Aliasing = B_dev_aliased - B_dev_cleared;

%% Displaying the results:

% setting a fixed intensity window, for good visual validation:

close all;

intensityWindow = [min(B_dev_cleared(:)), max(B_dev_cleared(:))];

scrsz = get(0,'ScreenSize'); % full screen looks better

figure('Position', scrsz, 'Units', 'normalized');

axes('Position',[0 0 1 1], 'Units','normalized');

% the result without zero-padding

subplot(1,3,1);

imagesc(squeeze(B_dev_aliased(My, :, :))',intensityWindow);axis equal tight

text(Nz*0.95,My,'\rightarrow','HorizontalAlignment','right','fontsize',35)

text(Nz*0.65,My*1.1,'aliasing','HorizontalAlignment',...

'right', 'fontsize', 12)

title('Result without aliasing prevention',...

'fontsize', 12);

xlabel('axis perpendicular to B_0 \rightarrow');

ylabel('B_0 direction \rightarrow');

% the estimated aliasing distribution

subplot(1,3,2);

imagesc(squeeze(Aliasing(My, :, :))',intensityWindow);axis equal tight

text(Nz*0.95,My,'\rightarrow','HorizontalAlignment','right','fontsize',35)

text(Nz*0.65,My*1.1,'correction','HorizontalAlignment',...

'right', 'fontsize', 12)

title(strcat('Estimated aliasing distribution', ...

' (calculated in low-res)'),'fontsize', 12);

xlabel('axis perpendicular to B_0 \rightarrow');

ylabel('B_0 direction \rightarrow');

% the final result of using virtual zero-padding:

subplot(1,3,3);

imagesc(squeeze(B_dev_cleared(My, :, :))',intensityWindow);axis equal tight

text(Nz*0.95,My,'\rightarrow','HorizontalAlignment','right','fontsize',35)

text(Nz*0.65,My*1.1,'result','HorizontalAlignment',...

'right', 'fontsize', 12)

title('Final result of virtual zero-padding','fontsize', 12);

xlabel('axis perpendicular to B_0 \rightarrow');

ylabel('B_0 direction \rightarrow');

文件列表（点击上边下载按钮，如果是垃圾文件请在下面评价差评或者投诉）:

Fourier Based Field-shift for MRI源码程序/
Fourier Based Field-shift for MRI源码程序/CalculateFieldShift/
Fourier Based Field-shift for MRI源码程序/CalculateFieldShift/calculateFieldShift.m
Fourier Based Field-shift for MRI源码程序/CalculateFieldShift/demonstration.m

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