| Safer MRI Scans - Science Insider
Reported November 2007
BACKGROUND: Researchers at Johns Hopkins University have figured out how to safely perform magnetic resonance imaging (MRI) scans on people who have any one of 24 modern types of implanted defibrillators and pacemakers. They use a combination of methods to reduce the risk of life-threatening meltdowns and complications posed by MRI machines designed to charge and manipulate the electrical properties of cells in order to produce real-time images from inside the body.x
SAFETY TWEAKS: 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, thus preventing misfires. The researchers also turn off the defibrillators’ shocking function for the brief duration of the MRI scan, about 30 to 60 minutes. In addition, they changed the amount of electrical energy used at peak scanning in MRI: they reduced the strength of the electromagnetic field by half from as much as 4 watts per kilogram per patient. The lower-energy scan still provides images of sufficient quality to make an accurate diagnosis in more than 90 percent of the cases tested.
HOW MRI WORKS: Magnetic resonance imaging uses radiofrequency waves and a strong magnetic field instead of X-rays to provide clear and detailed pictures of internal organs and tissues. These radio waves are directed at protons in hydrogen atoms -- one of the most abundant atoms in the human body, because of the body's high water content. The waves "excite" the protons, and when they "relax," they emit strong radio signals. A computer can turn those signals into a high-contrast image showing differences in the water content and distribution in various bodily tissues.
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The American Association of Physicists in Medicine contributed to the information contained in the TV portion of this report.
If you would like more information, please contact:
David March, Public Affairs
Johns Hopkins School of Medicine
(410) 955-1534
dmarch1@jhmi.edu
Martha Heil
American Institute of Physics
for the American Association of Physicists in
Medicine
(301) 209-3088
mheil@aip.org
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