Dear John,
> A quick, simple question: in the gray/white matter segmentation maps the
> voxels value range from 0 to 1. What do these value mean? For example, if in
> a gray matter map I get a voxel with value 0.8, does it mean that this voxel
> is a gray matter voxel with probability of 0.8, or it contains 80% of gray
> matter volume, or something else?
The values that you get during segmentation are the probability that a
voxel belongs to a tissue class, based on its intensity and the prior
probability of a voxel at that location belonging to a particular
tissue class. But remember that many voxels will contain more than
one tissue class (i.e. "partial volume effects"); so a voxel that
contains 80% gray matter and 20% white matter will have a different
intensity than one that contains 50% gray matter and 50% white matter.
Thus, the probability can also be thought of as a volume of a tissue
type (or more accurately, proportional to the volume, which can be
calculated by multiplying the probability by the voxel volume).
Hope this helps!
Best regards,
Jonathan
--
Dr. Jonathan Peelle
Department of Neurology
University of Pennsylvania
3 West Gates
3400 Spruce Street
Philadelphia, PA 19104
USA
http://jonathanpeelle.net/
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