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MRIs Can Detect Blocked Arteries

4/9/2004      

FRIDAY, April 9 (HealthDayNews) -- A new way of using magnetic resonance imaging (MRI) allows doctors to see blood flowing in arteries and might one day replace invasive techniques to check for blockages, a new study suggests.

Now, if your doctor wants to see whether you have a blocked artery, he has to do a procedure called an X-ray angiogram. This involves using a "contrast agent," which is injected into the bloodstream to highlight the artery for the X-ray.

Then a series of X-rays are taken and the images are assembled by computer into a short movie that shows the doctor where the blockage is located.

While an angiogram is safe and effective, it's an invasive procedure and does involve radiation. In addition, contrast agents can sometimes have unpleasant or unwanted side effects, including kidney damage, according to the study authors from Duke University.

In contrast, MRI use harmless magnetic fields and radio frequency signals to image body tissues, the researchers said.

Using this new technique, "you can get images that look like those from an X-ray angiogram, but you can do it with noninvasive MRI," said lead study author Robert M. Judd, an associate professor of radiology and co-director of the Duke Cardiovascular Magnetic Resonance Center at Duke University.

Judd's team reports its findings in the April issue of Nature Medicine.

In their new approach, Judd and his colleagues have created a way to use MRI scanning to "excite" protons in blood cells as they flow in blood vessels. The scanner then detects that signal, which shows blood flowing through blood vessels.

"The technique is still new and there are technical issues that need to be sorted out," Judd said. "But the principle appears to be correct."

Using this technique, doctors should be able to locate a blockage in a blood vessel, and also any partial blockage by measuring the amount of blood flow above and below the blocked portion of the vessel, Judd said.

Judd said that hospitals would not need new MRIs to use this new technique. All that would be needed is an upgrade in software, he said.

Right now, however, the technique works only in large vessels, such as the aorta in the heart and the renal arteries that carry blood to the kidneys.

"Ultimately, you would like to be able to look at vessels in the heart and head, and that's one of the things we will work on over the next few years," Judd said.

Dr. Tony Fuisz, director of cardiac MRI at Washington Hospital Center in Washington, D.C., called the new research interesting. However, he said, "a new way to image segments of the aorta, renal arteries, and other large vessels is like an answer to a question no one is asking. The real Holy Grail is coronary [heart arteries] imaging."

According to Fuisz, there are a number of potential obstacles to using the new technique for coronary arteries. "Some of these obstacles involve fundamental physical limitations and as such may not be able to be overcome," he added.

"Most likely this technique will become a complementary method used in concert with other established techniques. I wouldn't scrap the X-ray angiogram suite just yet," Fuisz said.

Dr. Christopher Kramer, director of cardiac MRI at the University of Virginia Health System, agreed. "This is a very exciting new technique, but its ultimate clinical application needs further evaluation," he said.

Right now, one limitation to the technique is that you can only see a small part of any vessel at one time. Another is that it can only be used in large arteries, Kramer added.

The technique needs to be used in real clinical situations before its value can be determined, he said.

More information

The Rochester Institute of Technology can tell you more about MRIs, and the National Library of Medicine has information about angiograms.

SOURCES: Robert M. Judd, Ph.D., associate professor of radiology, co-director, Duke Cardiovascular Magnetic Resonance Center, Duke University, Durham, N.C.; Tony Fuisz, M.D., director cardiac MRI, Washington Hospital Center, Washington, D.C.; Christopher Kramer, M.D., associate professor of radiology and internal medicine, director of cardiac MRI, University of Virginia Health System, Charlottesville; April 2004, Nature Medicine

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