Dr. Ashburner and SPMers:
Two more questions arise while making a template using the standard VBM
protocol of Goode et al:
1.) When setting the normalization defaults, the program asks whether to
mask the template brain with a "default" or "specified" brain mask. I
have been selecting the default brain mask, but would prefer to use a
study-specific mask. Similarly, when selecting the images for
normaliization, the program asks to "select an object masking image". I
have been selecting the very same image that I am normalizing, reasoning
that the most specific mask for an image is itself. Is this a good approach
to finding an appropriate
brain mask ?
2.) The second question relates to how to select images from the whole
sample to use in the template. Goode et al chose 60 males and 60
females, matched on age and handedness, and then matched these to the entire
study group, also on age and
handedness.
I have selected 11 of 21 subjects for the template, whose age and
handedness do not differ statistically from the total group or the
other 10 subjects not used in the template. However, with such a
small sample, couldn't I make a study specific template using
all 21 subjects? Are there any methodological problems tto this
approach?
Regards,
Rob McClure
|