Novel X rays highlight clogging arteries.

Though doctors can gauge the degree to which a buildup of plaque is restricting blood flow, they would rather find incipient plaque long before these fatty deposits narrow vessels and cause angina and other symptoms of atherosclerosis. Scientists now announce a nuclear medicine technique that can do just that, quickly and inexpensively.

If the method works in people as well as it did in studies on rabbits, says David R. Elmaleh of Harvard Medical School in Boston, it could become a routine diagnostic exam for people at risk of atherosclerosis, much as a mammogram or dental X ray is for people at risk of breast cancer or tooth decay.

Elmaleh chemically linked technetium-99m--a short-lived, radioactive isotope--to a compound known as [Ap.sub.4]A which readily binds to purine receptors. Tissues in which plaque is developing contain copious amounts of these receptors. When [AP.sub.4]A was injected into rabbits whose arteries had been damaged to provoke atherosclerosis, more than seven times as much of the compound homed in on plaque as on healthy artery surfaces.

In X rays taken 15 minutes after the injection, Elmaleh's team pinpointed the plaque via its radioactive tag. The group reports its findings in the Jan. 20 Proceedings of the National Academy of Sciences.

What makes this technique "very, very interesting and promising," says H. William Strauss, chief of nuclear medicine at Stanford University Medical Center, is that it can pick up symptomless disease "when it may still be treatable, such as with diet or cholesterol-lowering drugs." It may also help identify "unstable plaque--the type that is able to rupture suddenly, causing a stroke or sudden cardiac death."

Moreover, because active plaque tends to attract the isotope-tagged compound, Strauss says, X rays of it would permit doctors to scout for recurrent disease in people who have undergone angioplasty or bypass surgery. This use "could be equally as important" as initial diagnosis of latent disease, he says.

Elmaleh's team has licensed the technology to Imaging Biopharmaceuticals of Cambridge, Mass., for development. Testing on people could begin in a year, says Elmaleh, the company's acting chief scientific officer.