Hi Freesurfer Experts,

Just as a followup through my reading i've come across posts which use qcache, mris_fwhm, mri_surf2surf or mris_smooth for smoothing. For my cortical thickness analysis I would like to smooth all of my rh/lh.thickness.fsaverage.mgh files for each subject in order to run a group analysis. After finding regions of difference, I would then like to use the ROI to extract each individual's mean thickness in the ROI in order to run a correlation with other measures. Based on this, I assume it would make sense to use smoothed data to identify the ROI and then use unsmoothed data for extracting actual thickness measures (does lh.thickness.fsaverage contain the original thickness or warped thickness values).

I am unsure which smoothing is the most accurate or preferred. In using qcache the smoothness of the images do not seem to reach the filter level (based on the earlier email) so I am not sure if there is a freesurfer tool to check the smoothness level or if the qcache smoothness levels make sense for cortical thickness.

Thanks,

Ajay

On Wed, May 4, 2016 at 5:41 PM, Ajay Kurani <dr.ajay.kurani@gmail.com> wrote:

Hi Freesurfer Experts,
I am trying to understand the difference between qcache option and mris_fwhm and which is appropriate for a cortical thickness analysis. I processed my files with qcache and have lh.thickness.fsaverage.fwhm15.gii (converted) files. I used an afni tool SurfFWHM to estimate the smoothness of a subject at when looking at the fwhm0 image it iwas 5.5 and for 10, 15 and 20mm it was approximately 9.3-9.9 smoothness level.

I also used mris_fwhm --hemi lh --s fsaverage --smooth-only --i lh.thickness.fsaverage.mgz --fwhm 15 --cortex --o test_15.gii and when using SurfFWHM on the smae subject the smoothness was estimated at 11.25.

1) I am not sure if the qcache or the mris_fwhm file is more appropriate to use for a cortical thickness analysis.

2) For qdec if I select the 15mm option does it assume the smoothness is 15mm when calculating monte carlo corrections? Would there be a different way to estimate this since my smoothness at 15mm is closer to 10mm?

Thanks,
Ajay