Hi: I was using SPM2 to compare the PET images of a family of patients
against normal subjects but am having trouble with the results. Wonder if
anyone may have some input and wisdom on what I have done wrong. Thank you
much in advance. Here is what I have done thus far:
1. Coregister each patient's/normal PET with his/her MRI
2. Spatially normalize patient's MRI with the normal template in SPM2
3. Write the transformation back to the PET images.
4. Express the values of PET SUV value as a ratio of basal ganglia (I
used PMOD to do this).
5. Using SPM2 --> PET --> Two sample T test
6. Compare a single patient against 9 normal subjects
7. Setting: No global normalization, no mean scaling, threshold absolute at
0.4 (and I tried from 0.3 to 0.8).
9. Define t-contrast [-1 1 0] as I want to see which parts of the patient's
brain has lower uptake than normal.
10. Set FDR p<0.05, Thresholds I tried from 0 to 200.
11. Save the overlay image --> Overlay with MRI.
As the attached jpeg image shows, the result is strange that it does not
follow any anatomic structure, but rather outlines the brain. I expect
difference between the patient and the normal in large areas (e.g., the
entire temporal lobe or more). I am quite puzzled... particularly I might
have missed something quite fundamental. Anyone has any idea?
Just FYI: some of my patients have cortical atrophy and venticular
dilatation. Would this affect the calculation?