Hi Christina,

You just need to calculate the fa parameter for each column of the DT.mat matrix and then reconstruct the image. One potential solution if you have MATLAB is to download spm8 and then run the script below. Alternatively, you may reconstruct the diffusion tensor for each voxel; dt = [DT(1,i) DT(4,i) DT(5,i);DT(4,i) DT(2,i) DT(6,i);DT(5,i) DT(6,i) DT(3,i)];, and then get the eigenvalues and solve the conventional equation. Hope that helps...

Best,

Russell

%fn_img: file path 'template' image (.nii) (eg b0 3D or 4D)
%fn_dt: file path to DT.mat (.mat)
%fn_fa: file path to new fa image to write (.nii)

hdr = spm_vol(fn_img);
load(fn_dt)
idx = sqrt(sum(DT.^2))>0;
fa = zeros(1,prod(hdr(1).dim(1:3)));
fa(idx) = sqrt(3.*sum([DT(1:3,idx)-repmat(sum(DT(1:3,idx))./3,3,1);repmat(DT(4:6,idx),2,1)].^2)./...
sum([DT(1:3,idx);repmat(DT(4:6,idx),2,1)].^2)./2);
hdr(1).fname = fn_fa;
hdr(1).dt = [16 0];
spm_write_vol(hdr(1),reshape(fa,hdr(1).dim(1:3)));