A woman with a history of obesity suffered burns on her breast during an MRI exam at Unity Hospital in Fridley last year, apparently when her skin came too close to the inner wall of the device, a state investigation has found.

The Minnesota Department of Health concluded that the hospital staff could have prevented the injury by taking extra precautions, such as adding protective padding, before the procedure.

A hospital spokesman said Monday that Unity regretted the incident, which was disclosed Monday in a report by the Office of Health Facility Complaints. The hospital has since taken steps to prevent it from occurring again, the agency said.

"Burns are a known risk of MRI procedures, especially among larger patients," said David Kanihan, a spokesman for Allina Hospitals and Clinics, which owns Unity. The magnetic devices can cause burns if a body part comes too close to the inner walls. Typically, patients lie on a table encircled by the device, and experts have warned that the procedure can be particularly dangerous for large individuals.

In this case, the unidentified patient, who was scheduled for weight-loss surgery, went to Unity in March 2008 and had an MRI scan for back and hip pain. A day later, a blister appeared on her left breast. During a follow-up scan several days later, a technician covered her with extra padding "to prevent burns," the report said.

But within a week, the blister had become infected and required wound care. The patient was later discharged to a nursing home, and had follow-up treatment at another hospital. A photo taken a month after the first MRI showed a "large, black and red burn" on the underside of her breast, the report said.

The Health Department cited the hospital for violating federal Medicare rules in connection with the incident. It said extra precautions, such as additional padding, could have prevented the burn.

But the hospital will not face any penalties because it has since taken corrective action, said Stella French, director of the Office of Health Facility Complaints. Among other things, the hospital provided mandatory safety training to MRI technicians. It also replaced the old MRI device with a new, larger unit. A hospital spokesman said manufacturers are making larger devices because of the growing rate of obesity.

Maura Lerner • 612-673-7384