Different cost functions, different minimization methods, and various sampling, smoothing, and
editing strategies were compared. Internal consistency measures were used to place limits on
registration accuracy for MRI data, and absolute accuracy was measured using a brain phantom
for PET data. All strategies were consistent with subvoxel accuracy for intrasubject, intramodality
registration. Estimated accuracy of registration of structural MRI images was in the 75 to 150 μm
range. Sparse data sampling strategies reduced registration times to minutes with only modest
loss of accuracy.