Hi Sven,
if you do have M0 calibration scans you >could< try to calculate absolute
perfusion values, merge these across sessions / subjects and use these as
a 4D confound.
However, usually the z-coverage of ASL is below that of the BOLD
acquisitions, i.e. you may need to cut down your analysis to the partial
volume of the ASL. Furthermore, if you don't have the calibration scans
you are lost.
You may consider to extract some reference ratios but I'm afraid there is
no region where you could safely assume that caffeine has no effect upon
it.
Hth,
Andreas
Am 19.03.12 11:56 schrieb "HALLER Sven" unter <[log in to unmask]>:
>Dear FSL expert
>
>I have a study aiming to assess the effect of caffeine on working memory
>
>I have a 2back working memory task. In a repeated measures design, each
>subject performs 2 days (one with placebo, one with caffeine), and 2
>2back tasks each day (total of 2x2 fMRI EPI BOLD runs per subject).
>
>The problem is that caffeine has a direct vascular effect. To capture
>this, each subject additionally has an ASL on each day. The idea is to
>assess the global CBF changes in ASL, and to eliminate this effect from
>the fMRI EPI BOLD analysis.
>
>I looked into the FEAT analysis, and there is in fact a perfusion
>analysis. Yet if I understood correctly, this analysis is rather intended
>for fMRI-like analysis of ASL instead of EPI data.
>
>Are there any suggestions how I could use the ASL data to extract
>medication-related changes in CBF from the fMRI tasks??
>
>Your help is highly appreciated
>
>Sven
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