Hello SPMers-
I am trying to figure out a reasonable heuristic for determining lower
limits for the size in terms of resels of a structure analyzed by Small
Volume Correction. In a recent helpful reply from a colleague in the SPM
group (http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0112&L=spm&P=R5690),
it was suggested that "it depends on the structure - I have recently used
five resels in the thalamus and lentiform and ten resels in cortical
regions." What are the qualitative and/or quantitative factors that would
determine these resel limitations for these structures?
Also, in second level (random effects) analyses, to what extent, if any,
could one relax the resel limit per SVC analysis? Particularly in second
level interactions (basic models, 2-sample t-tests on first level
contrasts) the SPM generated masks are messy and much more restrictive in
volume analyzed than simple second level comparisons (basic models,
single-sample t-tests on first level contrasts), resulting in widely
varying resel size. What is the tradeoff between resel size and resel
limit per analysis, particularly SVC analyses?
Thank you.
Brandall Y. Suyenobu, Ph.D.
Staff Research Associate
Brain Imaging Group
UCLA/CURE Neuroenteric Disease Program
Veterans Administration Greater Los Angeles Healthcare System
11301 Wilshire Boulevard
Building 115, Room 223
Los Angeles, California 90073
Tel: (310) 478-3711 ext. 40580
Fax: (310) 794-2864
http://www.med.ucla.edu/Cure
http://ibs.med.ucla.edu
http://mindbody.med.ucla.edu
|