Hi all, heat kernel smoothing and diffusion smoothing are supposed to give the same solution to an isotropic heat equation on the cortex. the difference is that heat kernel smoothing is simpler and there is no need to worry about the convergence. in diffusion smoothing, there might be a ringing effect (divergence) on smoothed data if "delta t" is not small enough. to avoid this problem, you may want to implement backward Euler scheme in solving the diffusion equation, which i haven't done. to avoid this instability problem, i developed the heat kernel smoothing. i feel heat kernel smoothing is far simpler and better approach than diffusion smoothing.
SUMA pacakage (AFNI add on) uses diffusion smoothing ported from my original MATLAB code but they are trying to replace with heat kernel smoothing soon. :) i am sorry i will fix the link on diffusion smoothing soon. moo. On 6/29/05, Doug Greve <[EMAIL PROTECTED]> wrote: > Hi Moo, > > I actually implemented your diffusion smoother but could not quite get it to > work. It might have been related to the delta t parameter. Can you give some > guidance as to how to set it? What's the difference between heat kernel > smoothing and diffusion smoothing? btw, the link to the "Diffusion smoothing > on cortex" software on your web page is broken. > > thanks > > doug > > > > > > > > > > Moo K. Chung wrote: > Dear Dr. Park, I guess you are asking about freesurfer related surface > smoothing. Although I am not exactly sure how FreeSurfer is implmenting > surface smoothing, the general theory of suface-based smoothing and FWHM > can be found in two of my previous publications: Chung, M.K., Worsley, K.J. > , Paus, T., Cherif, C., Giedd, J.N., Rapoport, J.L, Evans, A.C. 2001. A > Unified Statistical Approach to Deformation-Based Morphometry, NeuroImage > 14:595-606. http://www.math.mcgill.ca/chung/deformation/ni_deformation.pdf Chung, > M.K., Robbins,S., Dalton, K.M., Davidson, Alexander, A.L., R.J., Evans, A.C. > 2005. Cortical thickness analysis in autism via heat kernel smoothing. > NeuroImage > 25:1256-1265. http://www.stat.wisc.edu/~mchung/papers/ni_heatkernel.pdf These > softwares implemented in MATLAB can be found in my > webpage http://www.stat.wisc.edu/~mchung/softwares/sotfwares.html for > other type of triangular meshes. Moo. On 6/27/05, Hae-Jeong Park, PhD > <[EMAIL PROTECTED]> wrote: > Hi, I would like to know the relationship between number of iteration in > surface smoothing and Gaussian kernel size in FWHM. Would you give me some > information on this? Thank you in advance. Hae-Jeong -- Hae-Jeong Park, > PhD Assistant Professor, Department of Diagnostic Radiology, Yonsei > University, College of Medicine and Division of Nuclear Medicine, Severance > Hospital Director, Laboratory of Molecular Neuroimging > Technology http://neuroimage.yonsei.ac.kr Tel) 82-2-2228-2363, Fax) > 82-2-393-3035 Cellur) 82-10-4220-1003 > _______________________________________________ Freesurfer > mailing > list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > > -- Douglas N. Greve, Ph.D. MGH-NMR Center [EMAIL PROTECTED] Phone > Number: 617-724-2358 Fax: 617-726-7422 > -- Moo Chung http://www.stat.wisc.edu/~mchung Assistant Professor Department of Statistics University of Wisconsin-Madison _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
