I'm curious. Can a person who has perhaps a metal plate in their head or metal hardware to repair a broken arm/leg get an MRI? My gut says no.
I am extremely cautious and will not scan someone if there is any doubt about an implant.
Metal can cause distortion or signal loss. Sometimes even a small bit of metal will ruin a scan. (I've attached an example -- A tiny bit of Aluminum in a mask noseband caused loss of signal - the front of the head is gone)
Most orthopaedic implants like pins and screws are either MRI safe or MR Conditional. MR Conditional can be scanned if you follow manufacturer guidance. Either they aren't ferromagnetic or they aren't going anywhere once the bone has healed.
Aneurism clips are a NO SCAN. They don't have to be ferromagnetic. Moving around in a high magnetic field can induce a torque which can be catastrophic.
Along with the static field there are also rapidly changing magnetic gradients. The gradients can induce a torque. They can also induce a current in implants which can cause heating. Something to consider if someone ticks a yes box on the safety screening form.
A scanner uses brief RF pulses ~10kW (127.74MHz for a 3T scanner) There is a danger of RF burns if you happen to have a conductive loop that is close to resonance.
Source:
http://www.mrisafety.com/TMDL_list.php?mastertable=SafetyInformation&masterkey1=189