VoyForums
[ Show ]
Support VoyForums
[ Shrink ]
VoyForums Announcement: Programming and providing support for this service has been a labor of love since 1997. We are one of the few services online who values our users' privacy, and have never sold your information. We have even fought hard to defend your privacy in legal cases; however, we've done it with almost no financial support -- paying out of pocket to continue providing the service. Due to the issues imposed on us by advertisers, we also stopped hosting most ads on the forums many years ago. We hope you appreciate our efforts.

Show your support by donating any amount. (Note: We are still technically a for-profit company, so your contribution is not tax-deductible.) PayPal Acct: Feedback:

Donate to VoyForums (PayPal):

[ Login ] [ Contact Forum Admin ] [ Main index ] [ Post a new message ] [ Search | Check update time | Archives: 1, [2] ]

[ Next Thread | Previous Thread | Next Message | Previous Message ]

Date Posted: 14:25:00 12/17/02 Tue
Author: Dan Kimberg
Subject: x offset in BOLD data

Hi. I have a question about an issue we've noticed recently with some of our brain images. We've always pretty much assumed that our high-res anatomical images and our EPI BOLD images came out of the scanner roughly aligned, give or take a bit of head movement. Lately (the past year or so), we've been noticing that sometimes our EPIs are shifted a few voxels in x. That is, within each slice, the EPI data are shifted a few voxels over to the right -- data from the outside edge of the left hemisphere, on the right hand side of the image, end up out over the skull, and maybe a bit outside. The same is true for the scout images reconstructed on the scanner and the functional runs recon'ed offline.

The offset is the same across all the data from a single subject session, and the same across all slices. It varies between subject-sessions, however, and for most subjects there's no apparent offset. I would guess it happens about 15% of the time, but I haven't done a survey. The offset is always in x (left-right), and seems to be completely corrected just by shifting the EPIs until they nestle well within the T1s. We've been correcting it by hand, which I think is fine. But it would be nice to be able to calculate the offset from header information if possible, and do it automatically. I've poked around in the GE header a bit, but I don't have any documentation on what's in there, so it's a little hard to decode.

I can't say for sure that this issue is really new, but I don't remember seeing this earlier than about a year and a half ago. I could just be wrong about that. One thing that has changed roughly within this timeframe is that we switched from using "memp" T1s to higher resolution SPGRs. I know some folks at the CCN have had the same problem, but I don't know what they're using for anatomical images.

Obviously, even though we're switching to Siemens soon, it would be good to do the right thing for the GE data we already have. Any help would be greatly appreciated. Thanks,

dan

[ Next Thread | Previous Thread | Next Message | Previous Message ]

Replies:

[ Contact Forum Admin ]

Forum timezone: GMT-5
VF Version: 3.00b, ConfDB:
Before posting please read our privacy policy.
VoyForums(tm) is a Free Service from Voyager Info-Systems.
Copyright © 1998-2019 Voyager Info-Systems. All Rights Reserved.