The only correction for this problem is the change in hardware. The idea was
to recognize this artifact early on and request Siemens to do the fix. But
this obviously won't help with the data that was already collected.
peter
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
Of Katie Karlsgodt
Sent: Friday, March 25, 2011 12:53 PM
To: [log in to unmask]
Subject: Re: [FSL] Siemen's vibration artifact and Gallichan correction
Hi Darren,
I have tried a few approaches, which haven't been successful on our 64
direction data. Some of the things that don't work:
1. taking the signal within the region of the artifact, and covarying for
that signal in the fdt analysis (just got rid of most of the signal)
2. taking out the affected directions- for us, those seem to be any with x >
.6 or < -.6, and left us with 42 directions. this got rid of the artifact,
but decreased FA in the x direction fibers an average of 9% (tested in
subjects without the artifact). In some people it ranged up to almost 25%
signal loss.
3. we tried a version of the Gallichan correction but I'm not sure if it was
quite right as it didn't fix the issue- it sounds the same as what you
mentioned, subjects still had regions of artifact, although they seemed
smaller.
I'd also be very interested in hearing ways in which people have been able
to successfully implement a fix for this!
best,
Katie
On Mar 25, 2011, at 8:30 AM, Darren G wrote:
> Dear FSL
>
> Has anyone implemented the Gallichan correction for the Siemens vibration
artifact, and would you be willing to share your methods / scripts? We have
tried the implementation and had some success, but our data is only 35
directions, and I think the correction is not as robust with fewer
directions. Thus, we end up with some areas uncorrected; so we are
particularly interested if you have applied the method to data with a
similar number of directions.
>
> Thanks,
> Darren
_________________________________________
Katherine H. Karlsgodt, Ph.D.
Center for Cognitive Neuroscience
Department of Psychiatry
University of California, Los Angeles
email: [log in to unmask]
phone: 310-206-3019
fax: 310-794-9740
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