Dear FreeSurfers,
My apologies if this is mentioned in the release notes, but I couldn't find it with a quick search.
I'm using the following command to smooth some data:
mri_surf2surf --hemi rh --s average --sval in.mgh --fwhm 20 --tval out.mgh
Under FreeSurfer version 4.0.3, part of the output is: Reading in average area average/surf/rh.white.avg.area.mgh Approximating gaussian smoothing of target with fwhm = 20.000000, std = 8.493218, with 379 iterations of nearest-neighbor smoothing
Whereas under FreeSurfer version 4.1.0, I see: Reading in average area average/surf/rh.white.avg.area.mgh INFO: fwhm2niters: Fixing group surface area Approximating gaussian smoothing of target with fwhm = 20.000000, std = 8.493218, with 290 iterations of nearest-neighbor smoothing
It seems that there is less actual smoothing occurring for the same requested FWHM (unless the altered surface area estimate cancels out somewhere else?), is that correct?
Since the 20mm itself was fairly arbitrarily chosen in my lab, I'm wondering whether it would make sense to increase this to get the same number of iterations (on the same data) with the newer version, so that results are smoothed by the same amount. Is there a way of adjusting the FWHM to undo the effect of the above fwhm2niters fix?
Thanks, Ged
P.S. I realise that 4.1.0 is not exactly "new" itself... I'd also be interested to know whether this has changed again in more recent versions. Thanks!