Hi Carole,
So for each voxel in the brain, you want the correlation
with each of the 503 voxels in an ROI? That would be a
503 x 100000 element matrix, say. Is that right?
If so, then maybe 3dAutoTcorrelate will do that, where
the 503 voxel mask might be provided via -mask, and the
brain mask might be provided via -mask_source. Note that
the output would be a 530 'time point (voxel index)'
brain-masked dataset.
Please see the -help output for details. The 'Example'
there might match what you are doing.
- rick