I want to remove null (inactive) voxels from my analysis. I have an ROI mask. I want to restrict my analysis to the top 70% of active voxels within the mask. I have figured out how to use 3dBrickStat to get the numerical value of the 70th percentile of my data. However, I am stuck on how to mask by that. It looks like 3dmerge allows you to use a mask but not to specify a value (mrange) within that mask...
If there is a more efficient/straightforward way to accomplish this, that would be fine too.