Dear All,
We are working on atrophy correction based on T1 values of individual voxels This is outside of SPM. We wonder if atrophy correction could be done inside SPM by entering PET/SPECT and T1 MR images without the correction we are working on. The resolution of T1 MRI will be adjusted to the resolution of PET/SPECT images based on point-spread function for individual voxels. Therefore, spatial resolution of PET/SPECT and the resolution-adjusted T1 MRI is the same for individual voxels.
Let's assume that we compare patients and healthy controls. Patients may show decreased uptake of radiotracer but it may be due to the decrease in gray matter volume. We want to separate the source of the decreased uptake. It may be due to the decreased uptake per gray matter volume, decreased gray matter volume without change in the uptake per gray matter volume, or both.
Enter four sets of images, 1. patients' PET/SPECT, 2. controls' PET/SPECT, 3. patients' resolution-adjusted MRI, and 4, controls' resolution-adjusted MRI.
How can we interpret the results by the contrast
-1+1-(-1+1)?
Will this contrast pick up the regions where the decrease in tracer uptake is significantly greater than the decrease in gray matter volume?
However, the noise of the images is of course different. PET/SPECT images are much noisier. We wonder if images with different noise levels could be entered in the same analysis. Or do we need to add noise to the resolution-adjusted T1 MRI?
Another concern is that spatial normalization may partially correct gray matter atrophy. In the nonlinear algorithm, thin gray matter could become thicker? Do we need to partially disable nonlinear algorithm in spatial normalization?
I appreciate your help.
Sincerely,
Masahiro Fujita, MD, PhD
Assistant Professor
Department of Psychiatry
Yale University School of Medicine
VA Connecticut/116A2
950 Campbell Avenue, West Haven
CT 06516, USA
Tel: +1-203-932-5711, x3335
Fax: +1-203-937-3897
E-mail: [log in to unmask]
