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
