You'll need to account for scanner as a covariate. Hopefully, each scanner had subjects from all patient and control groups.

There are likely other differences as well between scanners (e.g. FOV, matrix size, TR, TE, etc.).

Images do not have pixels (picture elements), they have voxels (volume elements). The voxel size is determined by: (1) slice thickness; (2) matrix size; and (3) Field of View (FOV). The slice thickness gives you 1 dimension and FOV/matrix gives you the other two dimensions.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Mon, Feb 3, 2014 at 6:32 AM, Emma Burton <[log in to unmask]> wrote:

Dear List members

I am looking to process data using VBM, however the images (diseased groups) have been acquired on different scanners (all 1.5 Tesla) and at different centres. The images are all T1-weighted but the pixel dimensions differ.....

My concerns are is it possible to perform VBM analysis if I were to account for scanner site in the design matrix and get sensible results? also what is the potential impact (if any) of using data with different pixel dimensions. Are there any other things I should consider?

I would be grateful for any comments, sugggestions or tips regarding such analysis.

Kind regards

Emma