I was hoping someone could help clear up some confusion regarding the jd images produced by the longitudinal toolbox in SPM12.
In spm_pairwise the jacobian difference image is calculated as dat.jac{2} - dat.jac{1})/tdif(i)
Since the Jacobians encode the change from the average time point to time 2 or from average time point to time 1, shouldn't the difference be divided by the time difference from average to time point or tdif(i)/2 to give the rate of change from average to time point? Or is this already accounted for in other processing steps?
Thank you,
Suneth Attygalle
ADNI/Imaging Core Study Coordinator, Memory and Aging Center
University of California, San Francisco
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