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Preventing injuries caused by MRI

MAGNETIC RESONANCE Imaging (MRI) is a uniquely beneficial medical imaging modality. Just as any medical procedure, MRI procedures also have potential for certain hazards. On May 10, 2005, the US Food and Drug Administration issued a public health notification on MRI-caused injuries in patients with implanted neurological stimulators.

The FDA received many reports of serious injuries, which included coma and permanent neurological impairment in patients with implanted neurological stimulators as they underwent MRI procedures.

The FDA noted that these adverse outcomes might be due to the heating of the electrodes at the end of the lead wires, causing injury to the tissues surrounding the electrodes.

The FDA cautioned that besides stimulators for brain and vagus nerve, any type of neurological implant such as stimulators for the spinal cord, peripheral nerve and neuromuscular system could cause injuries.

Precautions needed

A physician who implants or monitors patients with implanted neurological stimulators must explain to the patient what MRI procedures are and stress that they must consult with the monitoring physician before having any MRI procedure to find out whether it can be performed safely.

Specialists who use MRI equipment must carefully screen all patients for any implanted devices prior to carrying out an MRI procedure, even if the device has been turned off.

They should also question the patients about devices that have been removed. Leads or portions of leads may often remain in the body and may act as antennae and get heated.

If the patient has an implanted stimulator, specialists using MRI may consult with the referring physician to discuss other imaging modalities. For some implanted neurological stimulators, MRI procedures are contraindicated and cannot be performed.

Inspired by the reported closed calls within the Veterans Administration Medical Centers, John Gosbee and Joe DeRosier wrote a magnetic resonance imaging hazard primer.

It lists many examples of MRI hazards, describes what makes these hazards tricky and makes a few recommendations. The primer also refers to other groups working in the area.

Five types of hazards

They identified projectile effect, twisting, burns, image artifacts and device malfunction as the five types of MRI hazards. MRI devices make use of magnets of high strength.

Pulling of magnetic material towards the magnet causes projectile effect. The authors cautioned that a hairpin near an MRI magnet can reach speeds of 40 miles per hour!

Intense magnetic field may force magnetic cochlear implants or cerebral aneurism clips to twist in the body.

Magnetic components may rip loose causing device failure or patient injury; tattoos or tattooed eye-liner containing iron oxide have heated to cause minor burns; major burns can result from looped electro cardiogram leads and MRI accessories such as radio frequency coil leads in contact with a sedated patient.

Currently, MRI equipment is rare in our hospitals. But their numbers are increasing. Not many patients with implants may arrive at our hospitals for MRI examinations. This may soon change. Patients and physicians handling MRI equipment should be aware of MRI hazards to derive full benefit from this unique diagnostic tool.

K.S. Parthasarathy

Former Secretary, AERB
ksparth@vsnl.com

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