Dear SPM experts
I would like to compute the SNR of two T1-w. MRI scans of the same subject
derived from two different scanners. In the past, I used three VOIs. One VOI
was placed on the head of the caudate nucleus (grey matter mean signal), one
on the splenium of the corpus callosum (white matter mean signal), and the
last VOI was placed outside the brain (standard deviation of noise). This
seems to be the standard procedure to compute SNR.
But, I'am interested in the cortical sheed (neocortex) only. Therefore my
questions:
1. Do the measures of SNR (CNR) in subcortical structures (caudate nucleus
and corpus callosum) is also representative for the cortical sheed?
2. There is a function in SPM (img_snr.m) that computes the SNR voxel-wise
across the whole image. With this function, the standard deviation used to
divide the mean signal is computed across the whole image (brain and
background) and not only across the background.
Does this kind of computing the SNR is also meaningful?
3. Are there better procedures to compute the SNR across the whole brain
such as using a mask for the brain to get the mean signal of tissue and one
mask for the background to get the SD of the noise?
Thanks in advance
Kindly regards
Jürgen
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Juergen Haenggi
Ph.D. (Dr. des.)
Division Neuropsychology
Institute of Psychology
University of Zurich
Binzmuehlestrasse 14, PO Box 25
8050 Zurich, Switzerland
0041 44 635 73 97 (phone office)
0041 76 445 86 84 (phone mobile)
0041 44 635 74 09 (fax office)
BIN 4.D.04 (office room number)
j.haenggi[at]psychologie.uzh.ch (email)
http://www.psychologie.uzh.ch/neuropsy/ (website)
http://www.juergenhaenggi.ch (private website)
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