[Mristudio-users] b-matrix from dicom header and from techs

[Jeff Sadino]

Hi Venkat,

We had the same question on our Siemens VA25A DTIs.  The Siemen's tech
support recommended a program called MRIConvert (
http://lcni.uoregon.edu/~jolinda/MRIConvert/) to extract the gradients.  I
don't have our tables in front of me, but the .8, 0, and .4 values seem
pretty close to what I remember.  Siemens said that they suspected the 1, 0,
.5 values were in the scanner direction and the .8, 0, .4 values were in the
patient direction, since I think Siemens automatically adjusts for that.
Just be careful when using the MRIConvert program to extract gradients,
since it flips the y sign for FSL purposes.

Cheers,
Jeff

On Fri, Jul 9, 2010 at 9:33 AM, Rajagopalan, Venkateswaran <rajagov2 at ccf.org
> wrote:

>
> Dear All,
>
> we collect our data from Siemens scanner. I got b-matrix from our MR techs
> for software version VA25A b matrix is as follows
>
>  0: 0.000, 0.000, 0.000
>  1: 1.000, 0.000, 0.500
>  2: 0.000, 0.500, 1.000
>  3: 0.500, 1.000, 0.000
>  4: 1.000, 0.500, 0.000
>  5: 0.000, 1.000, 0.500
>  6: 0.500, 0.000, 1.000
>  7: 1.000, 0.000, -0.500
>  8: 0.000, -0.500, 1.000
>  9: -0.500, 1.000, 0.000
>  10: 1.000, -0.500, 0.000
>  11: 0.000, 1.000, -0.500
>  12: -0.500, 0.000, 1.000
>
> I used dcm2nii software (to convert hem into nifti file for soem other
> purpose  i also gives me bvec and bval files) which gives me the following
> matrix from the dicom header file
>
> 0       0       0
> 0.89    0       -0.45
> 0       0.45    -0.89
> 0.45    0.89    0
> 0.89    0.45    0
> 0       0.89    -0.45
> 0.45    0       -0.89
> 0.89    0       0.45
> 0       -0.45   -0.89
> -0.45   0.89    0
> 0.89    -0.45   0
> 0       0.89    0.45
> -0.45   0       -0.89
>
> Since not only the values are different but +/- signs are also different in
> DW directions. So I am wondering whether any one could tell me which is the
> correct table to go with.
>
> Thanks
>
> Venkat
>
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