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| |  DG DISPATCH - RSNA: Imaging The Heart At Work: The Real-Time MRI Stress Test By W. A. Thomasson, PhD Special to DG News
CHICAGO, IL -- November 27, 2000 -- A technique that provides magnetic resonance (MR) images of the heart when it’s working its hardest can be completed within 30 seconds after completion of maximum exercise. From these images it is possible to measure such indicators of cardiac function as ejection fraction, ejection rate and percent systolic wall thickening. The technique thus provides an exercise stress test in which cardiac function is measured directly. The technique’s success was discussed by J. F. London, MD, and colleagues from the US National Institutes of Health, Bethesda, Maryland, and the University of Virginia Hospitals, Charlottesville, Virginia, at the annual meeting of the Radiological Society of North American, being held this week in Chicago, Illinois. As Dr. London mentioned, previous MR techniques have provided clinically useful images of the beating heart and allowed measurement of cardiac function. These techniques, however, called for the patient to hold his or her breath while the image was acquired. This ruled out images during or immediately following exercise, and meant that only pharmacologically induced ischemic stress could be studied. With the new technique, based on electrocardiograph-gated real-time cine MR imaging, the subject enters the imaging machine immediately following maximally tolerated exercise and imaging is completed within seconds while subjects continue to breath at will. Breathing causes the portion of the heart imaged by any given slice to change continually, but does not affect image quality or the ability to measure cardiac function. All measurements to date have been on healthy volunteers. A physician in the audience asked whether the apparent up-and-down motion of the heart would make it impossible to follow specific regions and, therefore, to see the regional effects of ischemia that are so important in the cardiac patient. Dr. London anticipates that the potential difficulty can be overcome by increasing the scanning time per slice and possibly by adjusting the reconstruction to hold diaphragm position constant.
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