MRI cannot be used in the following circumstances:

In patients with:

• a heart pacemaker
• a metallic foreign body in the eye
• metallic vascular aneurysm clips
• a cochlear implant
• on life support systems which use ferromagnetic materials

The safety of MRI in pregnancy has not been determined and so MRI should be avoided in pregnant patients.

Surgical staples, plates, pins or screws, intrauterine device (?the coil') pose no risk during MRI if they have been in place for more than 4-6 weeks.

Tooth fillings are not affected by the scan, although their presence may distort MRI images of the facial area, so you should alert your radiologist if a head scan is being performed.

Alert: http://www.fda.gov/cdrh/safety/neurostim.html