Cath Lab Digest - December 2007 - (Page 4) 4 CLINICAL EDITOR’S CORNER DECEMBER 2007 EDITORIAL Which Devices are Safe for Magnetic Resonance Imaging? MORTON KERN, MD Clinical Editor Clinical Professor of Medicine Associate Chief Cardiology University of California Irvine Orange, California LAURIE GUSTAFSON Executive Editor Y our patient just had an left anterior descending (LAD) coronary stent implanted last week and calls the cath lab to ask when he can have a magnetic resonance imaging (MRI) examination so his knee surgery can proceed. Do you know which metallic implanted devices are safe for MRI imaging? REBECCA KAPUR Managing Editor ELIZABETH MCTAMNEY Layout/Production Manager MORTON KERN, MD Clinical Editor Clinical Professor of Medicine Associate Chief Cardiology University of California Irvine Orange, California mortonkern005@hotmail.com Any magnetic component within an implanted device may move toward the magnet and thus change the activity of that device (e.g., pacemakers). We well know that many metallic devices implanted in the heart may create problems in the very intense magnetic field of MR imaging. From several excellent reviews,1,2 we can better appreciate the interaction of magnetic resonance imaging and the metallic devices we implant in patients. It is important to recognize that there are three mechanisms of strong magnetic fields which may produce risk to patients. These are: 1. The attraction effect of a static magnetic field. 2. The electric current generation effect of a gradient magnetic field. 3. The heating effect of focused radiofrequency energy emitted by the MRI scanner. The static magnetic field of most MRI scanners (independent of MRI activation) ranges from 1.5 to 3.0 Tesla. The magnetic strength of these devices (which are always on) is 25-75,000 times the strength of the magnetic field of the earth. The risk from a static magnetic field is the attraction of a ferromagnetic object into the scanner with rapid acceleration, making the object a projectile. The attractive effect may also cause an implanted device to be moved, dislodged, or travel toward the magnet. Similarly, any magnetic component within an implanted device may move toward the magnet and thus change the activity of that device (e.g., pacemakers). The responses of metals vary with higher magnetic field strengths. Some devices which will not be affected by 1.5 Tesla may be greatly affected by a 3.0 Tesla. A gradient magnetic field is used to produce an image from the MR scanner by changing the magnetism (i.e., the intensity of the Tesla) quickly over each second of the measurement period. Recall that electricity can be produced by spinning a magnet inside tightly coiled wires. Thus, the rapidly changing magnetic gradient fields may induce an electrical field within metallic conductive wires and leads, which may then cause arrhythmias. However, this is a relatively uncommon event given the strengths of most MR magnets. Gradient fields may produce microvoltages that can produce ECG aberrations and alter the appearance of the electrocardiogram. Occasionally, inappropriate inhibition of pacemaker function or creation of an arrhythmic artifact on loop recorders may occur in large gradient fields. The third effect of MRI is the generation of radiofrequency energy (RF). During MR imaging, RF energy is pulsed into the body to alter cellular magnetic fields and generate the MR image. The RF energy is pulsed in, and the resultant energy PAUL MACKLER President/CEO PETER NORRIS Executive Vice President/General Manager JEFFREY MARTIN Vice President/Group Publisher Cardiology Division ALEX SLONIM Vice President/Associate Publisher of Cardiology CARSON MCGARRITY Senior Account Director NICK OTRANTO Account Manager LUCINDA BESKA Classified Advertising Sales Manager FRED KLUMPP Manager of Information Systems KATHY MURPHY Production Director STEFANIE TULEYA RENEE OLSZEWSKI Special Projects Editors KIMBERLY B. CHESKY Production Director, Special Projects PATRICIA LEVY Director of NACCME CIRCULATION: Bonnie Shannon Tel: (800) 237-7285, ext. 246 or (610) 560-0500 ext. 246 E-mail: BShannon@ hmpcommunications.com SUBSCRIPTION INFORMATION CATH LAB DIGEST is sent to all nonphysician cath lab personnel working in the United States (international subscription is $60 for 1 year). 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