All interpolation methods lose data by effectively smoothing the data because we're asking the computer program to generate data where none existed before. So we're making it up as best as we can using a number of interpolation methods. In most cases, this is normally acceptable as long as it's not done repeatedly. You should examine the data carefully to see the effect of the interpolation. By looking at the differences (or rations) between your original and your doubly translated dataset using 3dcalc might give you a good idea of the magnitudes and locations involved.