afni.nimh.nih.gov

siemenstoafni is Fred Tam's program. The last I had heard of it was almost 10 years ago, so I can't offer too much advice here other than to contact him (fred.tam @ sri.utoronto.ca ). Dimon, to3d (both in AFNI), dcm2niix (provided by Chris Rorden) and mri_convert (by Doug Greve with the FreeSurfer package) are all good alternatives.