Researchers at Johns Hopkins have painstakingly figured out how to safely perform magnetic resonance imaging (MRI) scans on men and women who have any one of 24 modern types of implanted defibrillators and pacemakers.

Henry Halperin, M.D., and his team have developed a combination of methods that reduce the risk of life-threatening meltdowns and other complications posed by MRI's ability to charge and manipulate the electrical properties of cells to produce real-time images from inside the body.

"We have turned a once exceptional procedure into one that is now a routine at Hopkins," Halperin says.

Among other things, the Hopkins group reprograms the devices, fixing them to a specific sequence. This makes the implanted devices "blind" to their external environment, reducing the potential for their electronics to confuse the radiofrequency generated by the MRI with an irregular heartbeat and preventing misfires. They also turn off the defibrillators' shocking function for the brief duration of the MRI scan, about 30 to 60 minutes.

Also changed is the amount of electrical energy used at peak scanning in MRI. The Hopkins team reduced the strength of the electromagnetic field by half, from as much as 4 watts per kilogram to 2 watts per kilogram per patient.

"This lower-energy scan still provided images of sufficient quality to make an accurate diagnosis in more than 90 percent of cases tested," Halperin said in an article published in the Sept. 18 issue of the journal Circulation, reporting on 55 of more than 100 patients scanned at Hopkins so far.

Their report comes just two years after the same journal published the team's initial, positive findings in animals, stirring fierce debate at several international conferences as to whether or not MRI could truly be made safe.

Since 2004, the Hopkins team says its expanded use of MRI has made more than a dozen potentially life-saving diagnos
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Contact: David March
dmarch1@jhmi.edu
410-955-1534
Johns Hopkins Medical Institutions
18-Sep-2006