Hi - yes you can think of a PVE image as telling you the estimate of the
fraction of a voxel's volume occupied by that tissue type.
Your second question raises some of the philosophical issues relating to
VBM, but I think the simplest answer is that yes it is doing what you
think it is doing.
Cheers.
On Fri, 28 Nov 2003, Mike Milham wrote:
> Hi! I have been using FSL's tools for VBM analyses and have the following
> question - I'm sorry if this may seem obvious, but I wanted to be sure on
> this one - If I understand the pve maps in FSL correctly, they appear to
> be equivalent to the modulated data that is becoming increasingly common in
> the SPM world - as they both appear to be able to provide voxel-wise volume
> measurements? Am I correct about this or am I misinterpreting something?
>
> If so, then if I run through a vbm-like path using the PVE's and toss in
> total gray matter as a covariate in my model (to correct for diffs
> resulting from differences in intra-cranial volume and/or those introduced
> by normalization), then am I correct in assuming that my differences can be
> legitimately interpreted as differences in voxel-wise volume?
>
> Thanks
> Mike
>
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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