Exclusions and Contraindications Patients and volunteers will generally be excluded if any of the following contraindications are present:

1. MRI Contraindications or Relative Contraindications:
1. Brain Aneurysm Clip
2. Implanted neural stimulator
3. Implanted cardiac pacemaker or defibrillator
4. Cochlear implant
5. Ocular foreign body (e.g. metal shavings)
6. Other implanted medical devices: (e.g. Swan Ganz catheter)
7. Insulin pump
8. Metal shrapnel or bullet.

2. In addition the following patient groups will be excluded unless specifically recruited into an NIH protocol:
1. Pregnant women (Patients who are uncertain as to whether they are pregnant will be required to have a screening urine or blood pregnancy test)
2. Patients with surgery of uncertain type where the presence of metal clips or wires cannot be excluded.
3. Patients with unstable angina or New York Heart Association functional class IV heart failure

3. Furthermore, the following patient groups will be excluded from studies involving the administration of MRI contrast agents:
1. lactating women
2. patients with hemoglobinopathies
3. renal disease (CrCl < 20 ml/min)

Note: These criteria are more rigid than standard clinical practice because we hope to avoid any complications in research subjects. General clinical criteria for MRI safety are available on the internet and in textbooks.