Hello-
Our group occasionally encounters patients with various syndromes such that 'excessive' head movement is an issue. One solution on which we rely is acquiring an "accelerated" MPRAGE sequences (Siemens GRAPPA) which takes about ½ the time. For those not familiar with this method, the resulting image is noisier and the contrast-to-noise is reduced. Quantitatively, because of the increased noise in the accelerated acquisition, comparisons of the correlation between regional cortical thickness reveals that the covariance is different between data acquired with the accelerated vs. non-accelerated sequences.
If the longitudinal processing stream is used, is the issue of differing covariance between the 2 acquisitions method an issue? If so, does anyone have a suggestion about to deal with this issue?
I should add, there is no systematic issue such as one patient group always requires using the accelerated sequence.
Regards, Wil