- Contraindications to MRI, including: subjects with intrathecal pumps, stimulators, pacemakers, aneurysm clips, non-removable hearing aids, or metal fragments in the eyes. Other exclusion criteria include the inability to lie flat on the back for 40 minutes at a time or a self-reported history of claustrophobia. Subjects with a history of hip replacement and those with well-documented, verifiable, MRI-safe cardiac stents will not be excluded from the study.