Hello,

When using 3dmaskave across different data sets which have the same sized voxels, and no specific threshold, I expected the number of voxels per ROI which survived to be the same, and that isn't turning out to be the case. I'm trying to figure out if this is a systematic problem or not. For example, I created a mask with several ROIs, all the exact same size and on one group of data running 3dmaskave tells me that 19 voxels survive for every ROI, the same number of voxels per ROI, per person. This is what I expected as all ROIs are exactly the same size and there's no specific threshold given, thus I imagine it is just giving me the average time series for every voxel in an ROI of that size. However, when I brought the same mask over to a different data set, it is now giving me, not just different values surviving per ROI than in the previous data set, but also different values surviving within this new data set..for example, ROI 1 has 68 voxels surviving, ROI 2 has 61 voxels surviving..The voxel sizes for both data sets are the same..The only thing that is shifted is the dimension(LPI). I had to shift the mask to be aligned with the new data set..even if that somehow changed the number of voxels which survive, I would still expect it to be consistent(i.e. 68, 68, etc.). This seems like a rather simple issue, I'm not sure what the problem is. I appreciate any help!

Thank you
Sam DeWitt