Hallo,
I perfomed VBM on 59 subjects in SPM8 using New Segment and DARTEL. Statistics (regression analyses according to 3 groups with
different musical expertise: non musicians, amateur pianists and experts pianists) yielded plausible and nice results.
However, I was surprised not to find differences in the motor areas. I then discovered that gray matter density values
on top of the head are really low (mean around 0.2, for the rest of the head> 0.7)..
During the MPRAGE on a Siemens 3-T we corrected automatically for regularization bias:
MPRAGE resolution> filter: prescan normalize activated. Furthermore, in New Segment I did a bias correction
(very light regularisation (0.0001), 60mm cutoff), I saved the Bias Corrected, and compared the bias corrected images
to the original, that improved slightly, and seemed to have relatively good overall intensities.
I have 2 questions:
- How to explain that the VBM values are so low on top of the brain
- What is a reasonable relative mask value to use for the statistics
Best, Clara James
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Dr. Clara JAMES
Faculty of Psychology and Educational Sciences
Geneva Neuroscience Center
University of Geneva
Uni Mail, 40 Bd du Pont-d'Arve
1205 Geneva, Switzerland
Tel. : 022-3799264
Fax : 022-3799229
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