Researchers have used a specialized type of MRI to detect 88 percent of cases of coronary artery disease in a group of patients with chest pain. The results suggest that the imaging technique can detect heart disease as accurately as conventional methods, but with much less risk.
Coronary artery disease is the most common form of heart disease and the leading cause of death in the United States. It occurs when fat and calcium accumulate in the arteries that supply blood to the heart. Over time, less blood reaches the heart and heart muscle dies. If the plaque blocks the arteries completely, a heart attack occurs.
Currently, the best way to detect the disease is coronary angiography. A physician threads a tube into the heart, releases a dye, and uses X-ray images to look for decreased blood flow. But there’s a small risk in this procedure that the tube will pierce an artery, resulting in bleeding, or else scrape plaque from artery walls, which, once the chunks of plaque are in the blood stream, can lead to heart attack or stroke. Other, noninvasive tests such as cardiac ultrasound are less risky, but not as accurate. Ultrasound images can be poor in patients with other conditions such as obesity, requiring doctors to resort to invasive tests.
While MRI allows doctors to image the body using magnets and radio waves, until recently it could not produce clear images of moving objects, such as a beating heart. In the past two years, though, stronger magnets, more powerful computers, and new software have improved MRI. “Recent developments allow us to acquire images of the heart in motion,” says Ricardo Cury, director of clinical cardiac MRI at Massachusetts General Hospital in Boston and leader of the study. Doctors can now watch the heart beating in real-time. And the images are now sharp.
“It’s like opening up the heart and looking at it directly,” says Renato Santos, a cardiologist at Wake Forest University Baptist Medical Center (who was not involved in the research). “Until recently, MRI was a research tool,” says Santos. “Now it’s real a clinical tool…ready for prime time.”
Cury combined two cardiac MRI tests to improve the technique’s ability to diagnose coronary artery disease. In his study, published in the July issue of Radiology, researchers at MGH, Harvard Medical School, and Beneficencia Portuguesa Hospital in Sao Paulo, Brazil, examined 46 patients. They began with an MRI stress test, injecting a harmless dye and medicine that stresses the heart. As the heart pumped, they used MRI to look for decreased blood flow or evidence that the heart was working abnormally. Next, they examined still MRI images of the heart for damaged areas or evidence of prior heart attack. If patients were abnormal in one or both tests, the doctors deduced blocked arteries.
Cury’s results reinforce those of an earlier, unrelated study (abstract), in which researchers at Duke University used the same techniques to successfully diagnose coronary artery disease in 100 patients.
The results are good news for patients. The MRI exam is short and painless. By using it to triage people who have chest pain but may not have the disease, physicians might save some patients from unnecessary invasive procedures. In cases where the heart disease is evident, MRI can help doctors decide what to do next – for instance, whether surgery to clear or bypass a blocked artery is necessary. After surgery, doctors can use MRI to monitor arteries for future blockages non-invasively.
Cury says that the 12 percent of cases misdiagnosed in his study are less than other noninvasive tests, and in some cases artifacts of the study’s design. He adds that MRI’s accuracy will increase as doctors learn to make better diagnoses from MRI images.
“Obviously 100 percent [accuracy] is ideal,” says Santos. “I think MRI is going to get us closer to that than our traditional methods.”