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Radioactive imaging: snapshots of the heart.

Getting a precise idea of what's going on inside a living, beating heart without stopping it or removing a slice has long challenged cardiologists, who have come up with a variety of ways to go about it. At the recent American Heart Association meeting in Washington, D.C., researchers discussed two new methods that they say offer benefits over other techniques. One method shows atherosclerosis in its earliest stages, and the other outlines the exact portion of heart muscle injured in a heart attack.

The atherosclerosis imaging is done with low-density lipoprotein (LDL), one of the proteins that carry cholesterol in the blood. Robert S. Lees of the Massachusetts Institute of Technology and his colleagues from two Boston hospitals have devised a way to purify LDL from a person's blood, tag it with a radioactive substance and inject it back into that person.

Some of this "hot" LDL, like normal LDL, gets taken up by newly forming atherosclerotic plaques. Within a day of injection, the patient is "photographed" with a gamma radiation counter; the resulting picture shows the location of radioactive LDL, and thus where plaque is forming.

Lees and his colleagues have so far looked at 15 patients, who ranged from severely atherosclerotic to disease-free. The researchers have seen no adverse reactions to the regimen, possibly because use of the patient's own LDL keeps the body from mounting an immune response.

Lees hopes the technique will prove useful both as a way to find atherosclerosis before it becomes life-threatening and in monitoring the efficacy of anti-atherosclerotic treatments such as drugs or diet change. The process offers advantages of over other ways of detecting early atherosclerosis: It is safer than X-ray dye studies and more precise than ultrasound, Lees says.

Atherosclerosis can lead to a heart attack, and heart attacks present imaging problems of their own. Determining the extent of injury to the heart muscle is important because it lets doctors know how aggressively to treat a patient.

Dead heart cells release a protein, myosin. Ban-an Khaw, Edgar Haber and their colleagues at the Massachusetts General Hospital in Boston and at the biotechnology firm Centocor in Malvern, Pa., have developed a radioactively labeled antibody to myosin, which can be used to evaluate the extent of a heart attack.

The radioactive antibody is injected into a patient following a heart attack, and concentrates itself wherever there is extracellular myosin. Within about a day the radioactivity is checked on a gamma camera.

While curent imaging processes depict blood flow through the heart muscle, they don't necessarily differentiate dead tissue from tissue that is still alive but receiving little blood, notes H. William Strauss of Mass. General, who has been involved in the development of both the radioactive LDL and myosin antibody.

antimyosin is currently under evaluation at four U.S. institutions, and trials are scheduled to begin soon in Europe. Harvey Berger, who is using it at Emory University in Atlanta, has so far imaged about a dozen patients. He says he has seen no side effects, including no reaction against the antibody. But whether the process can be repeated on a patient, or whether the patient will eventually mount an immune reaction against the antibody, remains to be seen.
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Title Annotation:two new methods of heart imaging
Author:Silberner, Joanne
Publication:Science News
Date:Nov 30, 1985
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