Yes they should be opposite.

Peace,

Matt.

From: Qiuting Wen <[log in to unmask]>
Reply-To: FSL - FMRIB's Software Library <[log in to unmask]>
Date: Wednesday, July 2, 2014 at 4:21 PM
To: <[log in to unmask]>
Subject: Re: [FSL] Anyone make EDDY work with GE diffusion data?

The bvecs files are identical, but the eddy current distortions are in the same direction too... Are they supposed to go in opposite direction? If the diffusion gradients are the same, isn't it that the eddy current should be in the same direction?

Thanks,

Qiuting



On Wed, Jul 2, 2014 at 1:28 PM, Harms, Michael <[log in to unmask]> wrote:

Hi,
Have you confirmed that the bvecs you get are identical for the opposite PE acquisition, but that the eddy current distortions in the actual images clearly go in the opposite direction?

cheers,
-MH
-- 
Michael Harms, Ph.D.
-----------------------------------------------------------
Conte Center for the Neuroscience of Mental Disorders
Washington University School of Medicine
Department of Psychiatry, Box 8134
660 South Euclid Ave. Tel: 314-747-6173
St. Louis, MO  63110 Email: [log in to unmask]

From: Qiuting Wen <[log in to unmask]>
Reply-To: FSL - FMRIB's Software Library <[log in to unmask]>
Date: Wednesday, July 2, 2014 3:10 PM

To: FSL - FMRIB's Software Library <[log in to unmask]>
Subject: Re: [FSL] Anyone make EDDY work with GE diffusion data?

I tried acquiring only one b0 with opposite phase encoding gradient, as well as acquiring the whole diffusion data set with opposite phase encoding gradient. In either case it doesn't seem to work...

Qiuting


On Wed, Jul 2, 2014 at 12:42 PM, Matt Glasser <[log in to unmask]> wrote:
Did you acquire opposite phase encoding directions?  Usually people use eddy with that kind of data.

Peace,

Matt.

From: Qiuting Wen <[log in to unmask]>
Reply-To: FSL - FMRIB's Software Library <[log in to unmask]>
Date: Wednesday, July 2, 2014 at 2:15 PM
To: <[log in to unmask]>
Subject: [FSL] Anyone make EDDY work with GE diffusion data?

Dear all,

I've tested TOPUP with data from GE scanner and got very good and stable results. However, when I continue with EDDY it doesn't seem correct the eddy current distortion at all. However, I've heard a lot of good words about EDDY from people who use Siemens data. So I want to know if anyone in the forum ever made it work with GE diffusion data. 

I checked the diffusion directions and it does span the whole (not the half) sphere, and Jesper (from FSL) also helped me check I was using the correct command line and setup.

Thank you!

Qiuting

 

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