Dear list,
I just realized that there was an error in the SVC smoothness correction
formula I've posted a few months ago (see below). The correct formula is
FWHM = (V / RESELs)^(1/3)
Sorry for the confusion.
-Satoru
Satoru Hayasaka ==============================================
Post-Doctoral Fellow, MR Unit, UCSF / VA Medical Center
Email: shayasak_at_itsa_dot_ucsf_dot_edu Phone:(415) 221-4810 x4237
Homepage: http://www.sph.umich.edu/~hayasaka
==============================================================
At 09:37 AM 2/23/2005 -0800, Satoru Hayasaka wrote:
>Dear Elena & SPMers,
>
>At 11:00 AM 2/23/2005 +0000, Elena Antonova wrote:
>>How does one correct for smoothness in ROI? I was simply comparing the
>>smoothness (number of resels per voxels in the search volume) in the ROI
>>relative to the average smoothness of the whole image. Is there a
>>statistical procedure in SPM99 that allows correcting for smoothness in ROI
>>during SVC? Sorry, i'm not an expert, so would really appreciate your help.
>
>First you might want to find the smoothness within your ROI. If you have a
>binary mask for the ROI, then first you mask the RPV image and calculate
>the sum of all the RPV voxels in the ROI. This should give you the number
>of RESELs in your ROI. Then based on the RESELs, you can calculate FWHM as
>
>FWHM = V / (RESELs)^(1/3)
>
>where V is the number of voxels in the ROI.
>
>Once the smoothness is found, then you can change the smoothness for your
>SVC. In SPM2, this can be done by changing xSPM.FWHM variable with FWHM *
>[1 1 1] (FWHM in voxels). In SPM99, I think the name of the variable is
>VOL.FWHM. I haven't used SPM99 for a while...
>
>Hope this helps!
>-Satoru
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