Hello folks,
(Sorry for the delay, for some reason the message did not post when I wrote it a few days ago.)
As Nick said, there can be many reasons for the discrepancy and in some cases the error will depend on the shape of the ROI.
If you to measure the volume attributed to a surface patch, the best estimate is obtained with SurfPatch. Example 1 in that program's output shows how the volume is computed.
cheers,
Ziad
Edited 1 time(s). Last edit at 05/20/2013 09:11AM by ziad.