Hello,
We are investigating the effects of FAST on our fMRI BOLD data. Our paradigm is deep phenotyping of many (10+) scans per subject, collected at a TR of 0.46 with a multiband factor of 8 on a 3T Siemens PRISMA machine. We believe that accounting for autocorrelation is important under such circumstances but were wondering if SPM FAST is applied properly. We are concerned that the W matrices (whitening) produced by FAST produces extreme edge effects in the time-series data that do not look intended.
Attached is a figure showing the W matrices, and another figure illustrating the effect of W x g (session-level grand-mean scaling) on the time series data, summarized by the dot-product of a multi-voxel neural pattern of interest (Neural Pain signature). Notice that in the orange line, the beginning and the end of the data become extreme relative to the original data. Run-3 also exhibits a very strange oscillatory pattern that was not present in the original data.
Can someone help us shed light on this issue? Thank you very much.
