MRI test for coronary artery disease could replace invasive, costly angiograms
Wednesday, December 26th 2001, 12:00 am
By: News On 6
A new type of imaging technique using an MRI device can detect most diseased coronary arteries, potentially sparing many heart patients a more invasive, expensive and uncomfortable test, researchers say.
MRI, or magnetic resonance imaging, has been used for the past 10 years to study very large blood vessels such as the aorta. Patients must lie inside the MRI machine, a giant electromagnet that yields 3-D images of the body.
Now doctors at Beth Israel Deaconess Medical Center in Boston have adapted the technology to produce a series of high-resolution images of the relatively small coronary arteries.
Two smaller studies found the system could spot arteries blocked or narrowed by plaque in patients already diagnosed with coronary artery disease by the current ``gold standard'' test _ the X-ray-based angiogram.
A new study _ the first to try the system at several hospitals and on previously untested patients _ found it detected every diseased coronary artery in 75 percent of the patients and found the most life-threatening blockages in 89 percent.
The MRI technique is still not as thorough as an angiogram, but it is less invasive.
``This technique is a significant advance,'' said Dr. Valentin Fuster, director of the Cardiovascular Institute at New York's Mount Sinai Medical Center and past president of the American Heart Association. ``In five years, I think it's going to overtake the conventional angiogram.''
By then, Fuster expects advances will bring sharper images, allowing doctors to spot even tiny lesions that could eventually lead to heart attacks.
In an angiogram, a catheter is threaded from a groin or arm artery up to the heart. The catheter then injects a dye that can be seen on a ``movie'' X-ray, helping doctors spot blockages.
Angiograms produce very clear pictures but cause complications in about 1 percent of the 1.2 million patients getting the test each year, including a slight chance of artery damage or a heart attack. So researchers have been seeking a way to get similar results without the risks or other drawbacks.
The research on the MRI technique was reported in Thursday's New England Journal of Medicine. It was led by Dr. Warren J. Manning, head of noninvasive cardiac imaging at Beth Israel Deaconess.
The study involved 109 patients at Beth Israel and six other U.S. and European sites where staff had little experience with the new MRI system. Each patient first had the MRI test, followed by an angiogram.
The researchers got clear images of only 84 percent of the artery segments with the MRI test, compared with 100 percent for the angiograms, noted Dr. Rohit Arora, chief of cardiology and cardiac catheterization at University of Medicine and Dentistry of New Jersey in Newark.
``Blockages are still being missed'' by the MRI, he said.
The four main coronary arteries, with an inside diameter of only one-eighth of an inch, wrap around the outside of the heart and supply the muscle with blood. The arteries' small size and constant motion make it hard to capture images of them.
Overall, about 40 percent of patients who get an angiogram _ because a cardiac stress test indicated they might have coronary artery disease _ turn out not to have such disease, meaning they did not need the $5,000 test.
In those patients, doing just the MRI test would be sufficient and would cost only about $1,000, Manning said.
Still, the MRI test has drawbacks, such as requiring patients to lie inside the device for an hour, about three times longer than an angiogram takes.
Another type of heart imaging technology, called an ultrafast CT scan, is sometimes used in this country to detect calcium deposits in coronary arteries. With more refinements, however, the MRI technique could prove more useful by distinguishing between calcium deposits and more worrisome fatty build-ups, Fuster said. That, in turn, could help doctors spot patients in danger of a heart attack and start treatment promptly.