[Mrtrix-discussion] Question about the gradient direction table used in Mrtrix

[smxie_nlpr]

Hi,

I have a question about the gradient direction table used in Mrtrix. The gradient direction table achieved from the DICOM images with dcm2nii is different from the table achieved with the command 'mrinfo DICOMDIR -grad encoding.b'. I checked the source code of Mrtrix and found the following codes '
if(rotate_DW_scheme)
{
G(n,0) = image_transform(0,0) * d[0] + image_transform(0,1) * d[1] - image_transform(0,2) * d[2];
G(n,1) = image_transform(1,0) * d[0] + image_transform(1,1) * d[1] - image_transform(1,2) * d[2];
G(n,2) = image_transform(2,0) * d[0] + image_transform(2,1) * d[1] - image_transform(2,2) * d[2];
}' in image.cpp.
I transformed the original gradient table with similar code in Matlab, but the result is not equal to the table achieved with mrinfo. So I want to know the procedure of transforming the original gradients to the gradients achieved with mrinfo. And why is it 'G(n,0) = image_transform(0,0) * d[0] + image_transform(0,1) * d[1] - image_transform(0,2) * d[2];' rather than 'G(n,0) = image_transform(0,0) * d[0] + image_transform(0,1) * d[1] + image_transform(0,2) * d[2];' ?

Thanks.

Sangma Xie



Sangma Xie , Master  
Brainnetome Center 
National Laboratory of Pattern Recognition (NLPR)
Institute of Automation, Chinese Academy of Sciences (CASIA)
95 Zhong Guan Cun East Road, Hai Dian District, Beijing 100190, P.R.China
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