Basically, MRI’s are contraindicated for certain persons:
- Aneurysm clips (unless known definitely to be non-magnetic)
- Pacemakers / Cardioverters (device malfunction)
- Bullets, shrapnel, etc. (damage from metal moving)
- Ever worked in a metal shop where workers cut / hammered steel
The latter is because high-velocity tiny chips of metal can penetrate the sclera, which subsequently seals over & the person continues about their life, completely asymptomatic with normal vision. However, should they be exposed to an all-powerful magnet, that tiny metal fragment will be whipped back & forth throughout the eye [ugh]. Such persons can be screened by CT of the orbits, which will detect any potentially catastrophic shards. [I’ve always wondered if this complication had gotten thought out ahead of time, or got realized after a few bad outcomes].
Patients on dialysis can experience severe kidney damage from gadolinium contrast media, so most radiology departments won’t inject anyone with any degree of abnormal renal function.
Claustrophobic persons may require sedation, or imaging with an open MRI. Other unstable patients may not tolerate the procedure adequately for satisfactory results. The extremely obese or large may require an open MRI.