I am also confusing on this issue. According to Jonathan Farrell's website (
http://godzilla.kennedykrieger.org/~jfarrell/software_web.htm), the DTI
gradient tables are same for all subjects regardless of the slice
angulations if using "No Overplus" option. He also said " The V4.1 par files
list the diffusion weighting directions. HOWEVER, these directions are not
in pixel space. Specifically, in the case of gradient overplus = YES
tables, the directions need to be rotated and corrected for slice
angulation." My scans are using "No Overplus" option, If I am going to use
the gradient table listed in the PAR file, should I correct it for the FOV
or not?
So for the Philips 3T scanner, if using "No overplus" option, the gradient
tables are same for all subjects because they have been corrected already on
the scanner for the FOV. For my case, the bvec files used in FDT are same.
Am I right?
I haven't reached Jonathan Farrell. I would appreciate if anyone can confirm
on this issue.
Regards,
Wayne
On 05/05/09 7:03 AM, "Matt Glasser" <[log in to unmask]> wrote:
> Well, regardless of what option you select in the scanner, the gradients
> outputted by DICOM to NIFTI conversion programs like MRIConvert or MRICron's
> converter may vary from subject to subject if you have rotated the FOV. The
> gradients applied by the scanner are the same; they are just corrected for
> these rotations.
>
> Peace,
>
> Matt.
>
> -----Original Message-----
> From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
> Of Yuzheng HU
> Sent: Monday, May 04, 2009 11:36 PM
> To: [log in to unmask]
> Subject: Re: [FSL] gradient table for Philips 3T scanner
>
> Hi,
> Thanks for answer.
>
> I was told that '... if all subjects use same protocal, the gradients sould
> be
> same. however,for Philips, if you select "Overplus" option during scanning
> the
> gradients will be changed dynamically accordin to the tilt-angles...'
> The gradients I have might be in such cases.
>
> Best!
>
>
> Yuzheng
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