Hopefully someone can give some advice on this one…
Presumably, 3dvolreg will fail in correcting motion when large, sudden movements occur. I am analyzing an experiment consisting of several functional runs per subject and would like to exclude runs during which subjects moved too much. The question is, ‘how much is too much?’ The approach taken thus far has been to quantify whole-brain SNR (method of Parrish, TB et al., 2000) for each run and exclude runs failing to reach some criterion. The poor SNR could be due to a number of factors, however, so similarly quantifying motion for each run would be useful. Many strategies are possible, but I’m wondering if anyone has a suggestion for a criterion that has worked well for them in the past or is based on a deeper understanding of the circumstances under which motion correction fails (i.e. X number of movements greater than Ymm/degrees per Z volumes).
Any suggestions would be greatly appreciated.
Thank you,
-joel