MRI Technique Could Predict Heart Attack Risk
It tracks cholesterol-like molecules to show points of artery weakness
WEDNESDAY, March 28, 2007 (HealthDay News) -- An imaging technique based on the natural properties of "good" HDL cholesterol could someday help doctors spot patients at high risk of heart attack or stroke, researchers report.
HDL (high-density lipoprotein) cholesterol is beneficial, because it travels to the plaques that build up in arteries and removes the "bad" LDL cholesterol.
Now, researchers have developed HDL-like molecules that travel to the plaques and show up on MRI, giving doctors clear pictures of which plaques are most likely to rupture.
"Today, clinical diagnosis is really very poor, because our techniques have no way to predict which plaques are bad and which you can live with all your life," said Dr. Zahi A. Fayad, professor of medicine and radiology at Mount Sinai Medical Center in New York City. With the new MRI technology, "We can inject dye that goes to the spot of interest," he said.
The idea came from Dr. Edward A. Fisher of New York University, said David Cormode, a postdoctoral researcher at Mount Sinai who was slated to report on the work Tuesday at the American Chemical Society annual meeting in Chicago.
Efforts to get clear pictures of plaque buildup in arteries have been unsuccessful until now. That's because the contrast medium needed to produce images cannot pass through the lining of blood vessels. But Cormode -- who has a background in organic chemistry -- found a way to construct HDL-like molecules that carry the contrast medium through this lining.
In mouse studies, the team injected the animals with a modified HDL that carried gadolinium, a chemical long used in blood contrast agents. This method produced a 79 percent increase in plaque detection, Cormode reported. The effects of the injection also provided a viewing window of up to 48 hours.
The strength of the imaging signal correlated with the presence of inflammatory macrophage cells, which form centers of cholesterol accumulation.
"We target the inflammatory cells, macrophages," Fayad explained. By doing so, "we get a sense of macrophage density in plaque and can come up with a risk assessment," he said.
The researchers now are planning similar tests in larger animals such as rabbits. Some tinkering with the HDL molecules used in the mouse studies will be necessary, Cormode said.
The ultimate goal, of course, is a human test. Success would mean much better information about the exact degree of cardiovascular risk faced by an individual patient, Fayad said.
"We want to try to detect things much earlier than now and predict which patients require critical treatment," he said. "I'm not saying we would screen the whole population, but people at risk because of family history, age (age is very important), high blood pressure and other risk factors."
"For patients with a heavy plaque burden, we can start aggressive treatment to lower low-density lipoproteins and then do a repeat scan to see if the plaque is regressing," Fisher, who is professor of cardiovascular medicine at NYU, said in a statement.
The technique could also be used to used to follow patients who have heart attacks or strokes to see how well they respond to therapy, the researchers said. According to Fayad, if all goes well, the technique could be ready for use in humans in five years.
Find out more on cholesterol at the American Heart Association.