Dear Darren and others
Do any of you have experience with the Siemens Moco images for ASL, as these
are already 'motion corrected' would you recommend an additional image
realignment?
Also, I would be very grateful if you could send your matlab function for
tag to tag and control to control realignment that you mention.
Regards
Khalid
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Clinical Research Fellow,Department of Clinical and Experimental Epilepsy,
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-----Original Message-----
From: Darren Gitelman [mailto:[log in to unmask]]
Sent: 13 July 2005 15:56
Subject: Re: Perfusion MRI processing
my quick answer as I dash to rounds is that i think there are differences.
I can send a matlab function that realigns tags to tags and controls to
controls later today.
ciao.
darren
At 09:50 AM 7/13/2005, Geoffrey K Aguirre wrote:
>On Jul 13, 2005, at 1:03 PM, Ze Wang wrote:
>
>> For ASL images, I always realign them before subtraction, and
>>for realignment, I just follow the general procedure, although
>>Geoffrey
>>Aguirre recommends the separate realignment.
>
> Because the label and control images have systematically
>different image intensities, it seems wise to realign them back to
>separate label and control initial images. I have, however, never
>tested to see if this makes any substantive difference.
>
>>According to
>>JJ Wang's paper, spatial smoothing is very important for ASL images.
>
> The concept here is that whereas spatial smoothing of BOLD data
>is associated with some deleterious effects upon the intrinsic
>temporal noise structure, this unwanted effect is absent for ASL
>data. In other words, spatial smoothing of ASL data provides the full
>benefit that would be expected. There is no necessary incentive to
>smooth ASL data, however, beyond what would be desired to maximize
>detection of spatially extended signal changes.
>
> For those interested in the technical details: BOLD fMRI data
>have enhanced noise at low temporal frequencies. These low-frequency
>temporal fluctuations tend to share phase across space, so spatial
>smoothing of BOLD data acts to enhance the noise present at low
>temporal frequencies.
>
>Geoff
>
>--
>
>Geoffrey Karl Aguirre, M.D., Ph.D.
>[log in to unmask]
>Assistant Professor of Neurology
>Hospital of the University of Pennsylvania
>Center for Cognitive Neuroscience
>Philadelphia, PA
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Darren R. Gitelman, M.D.
Cognitive Neurology and Alzheimer¹s Disease Center
Northwestern Univ., 320 E. Superior St., Searle 11-470, Chicago, IL 60611
Voice: (312) 908-9023 Fax: (312) 908-8789
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