Dear Kohkichi Hosoda
> I'm trying to compare fractional anisotropy map of a patient with
> control database created from 26 normal volunteers to detect lesions
> after normalization and smoothing of all of them. What do you
> recommend in this kind of study (one patient compared with multiple
> controls), use global scaling & grand mean or skip them?
As one rule of thumb, you should not scale images, which are already scaled or where the voxel values are having a specific meaning or, more obvious, a unit; for example, quantified rCBF data from PET.
So, in your case, it depends on the pre-processing of your DTI data, but, I guess, that the voxel values in your anisotropy maps are reflecting the absolute degree of anisotropy, i.e. values between 0 and 1, with 0 = isotropy.
If that is the case, you should not scale individually.
Best regards,
Karsten
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Karsten Specht, PhD
Department of Biological and Medical Psychology
National Competence Centre for functional MR
University of Bergen
Jonas Lies vei 91
5009 Bergen
Norway
Tel.: +47-555-86279
Fax: +47-555-89872
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http://fmri.uib.no/
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