use "nearest neighbour" interpolation?
Or since your dataset is only translations, you could use 3drefit to change the coordinates of your dataset.
e.g. if you want to move the ROI 3 mm left and 2 mm superior, if your dataset is RAI, then
3dcopy myROI+orig myROI-translated
3drefit -dxorigin -3 -dzorigin -2 myROI-translated
check the sign of those dx's and such though...
Drew