3-D MRA: A safer, less expensive diagnostic
October 1, 1999 3 minutes read
3-D MRA: A safer, less expensive diagnostic
In essence, in about a half an hour, you’re done’
A simple 30-minute test may soon replace more invasive X-ray angiography to diagnose coronary heart disease, researchers report.1
Safer, cheaper, and more convenient, 3-D coronary magnetic resonance angiography (MRA) provides images of the coronary arteries without injection of a dye or exposure to X-ray. The cost of MRA is less than one-quarter that of an X-ray angiogram and causes patients considerably less discomfort and risk than the more traditional approach.
Another advantage of the technique is that the new methodology also can be used to evaluate the anatomy, contractility, perfusion, and valvular function of the heart, providing a comprehensive, noninvasive, cardiac examination.
Old method carries risk of infection
During conventional angiography, patients must lie still while a small tube is placed inside the blood vessels to deliver the dye. After vessels are X-rayed, the patient often must remain in the hospital for a recovery period of four to six hours.
The traditional procedure carries with it risk of infection and bleeding, and in a small fraction of cases, heart attack and stroke, wrote Warren J. Manning, MD, co-director of the Cardiac MRA Center at Beth Israel Deaconess Medical Center in Boston, associate professor of medicine and radiology at Harvard Medical School, and senior author of the study.
"We have multiple methods to try to determine if our patients have coronary heart disease," he wrote. "However, we have no methods to image the coronary arteries themselves that do not require injecting a dye into a blood vessel."
Done in a half hour
With the new MRA technique, sets of images of the blood vessels on each side of the heart are acquired. Each set of images takes 10-15 minutes during which time patients simply need to lie still and breathe normally. Individuals found to have blockages can then be treated with angioplasty or surgery.
"So, in essence, in about a half an hour, you’re done. It is likely that the technique will become the standard approach at many cardiac MRA centers because of its ease of use and high quality," says Manning.
The team first reported that MRA could be used for coronary artery imaging in 1993, Manning says, but the approach at that time required patients to hold their breath 30 to 40 times for about 16 to 20 seconds each time. Most patients could be trained to do that, but the images were not as clear as they could be. With the new MRA methods, patients no longer need to hold their breath, and image quality is improved.
In Manning’s study, eight healthy adults and five patients with confirmed heart disease underwent the new technique. The investigators reported that MRA compared well with conventional X-ray angiograms and, in fact, that there was improved definition of the arteries.
In a related development, the National Institutes of Health (NIH) announced in late June that it is launching a study of whether magnetic resonance imaging (MRI) should be used in emergency departments as a diagnostic tool to evaluate myocardial infarction (MI) and stroke.
This would be the first time that MRI would be part of a protocol to diagnose heart disease upon admission. It is hoped that the NIH study will show whether the technology can more quickly and accurately identify heart attacks and strokes so patients can benefit from earlier treatment. The four-year trial will be conducted at Suburban Hospital in Bethesda, MD, which will be equipped with two MRI scanners.
Patients with unquestionable MI on presentation will receive thrombolytic therapy, angioplasty, or other treatment and will undergo MRI after stabilization. Patients with an uncertain cause of chest pain on presentation will undergo immediate MRI. Patients with suspected stroke will undergo both computed tomography (CT) scans and MRI so that investigators can compare efficacy. If MRI proves to be as good or better than CT for seeing blood, MRI alone will replace both tests as a protocol for most stroke patients.
The new MRIs are more sensitive for detection of blood and can image cells that are ischemic but not yet infarcted. CT cannot do that. A whole MRI takes about 15 minutes, and the results are easier to interpret. CT takes about 10 minutes, but the results are more open to question.
Reference
1. Botnar RM, Stuber M, Danias PG, et al. Improved coronary artery definition with T2-weighted, free-breathing, three-dimensional coronary MRA. Circulation 1999; 99:3,139-3,148.
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