Strategies found to halve heart CT radiation dose

* Findings could make heart CT scans safer

* Lower dose CT scanners under development

By Julie Steenhuysen

CHICAGO, June 9 (Reuters) - U.S. researchers have found a way to cut the radiation dose from a heart CT scan by half without sacrificing the quality the scan, a finding that could speed adoption of such tests, they said on Tuesday.

Using computed tomography -- or CT scans -- to find heart disease allows doctors to see diseased arteries without having to do a more invasive angiogram, which involves threading a catheter through heart arteries.

"It's becoming increasingly popular as well as increasingly accurate as they develop better and better machines," said Dr. Gilbert Raff of William Beaumont Hospital in Royal Oak, Michigan, whose study appears in the Journal of the American Medical Association.

"You can actually see the arteries that cause heart attacks," Raff said in a telephone interview.

But recent studies have raised alarm about the scans, which expose patients to double, triple or quadruple the radiation exposure of an angiogram, raising cancer risks.

For people living in the United States, Raff said the normal expected radiation dose from chemicals in the ground or flying in an airplane is 3 milliseverts a year.

"We found the test was delivering on average about 20 millisevert," he said. "That is more than we want and more than we thought you needed for taking these pictures."

Raff and colleagues devised a formula to reduce the exposure by tailoring each scan to a patient's weight and heart rate. They tested it on nearly 5,000 patients undergoing cardiac CT scans at 15 hospital imaging centers.

"The whole thing is in the name of safety," he said.

The strategies included shortening the image they scanned, reducing a patient's heart rate using drugs and adjusting the voltage according to body weight.

Using these techniques, they were able to cut the estimated radiation dose by 53.3 percent.

Raff said the biggest factor affecting radiation dose was a patient's weight. They found you could turn down the voltage and still get good pictures in lighter patients.

"Reducing that voltage by 20 percent reduces the radiation dose by about 40 percent," Raff said.

He said using the strategies allowed physicians and radiology technicians to customize the exams.

The team developed the instructions with help from imaging equipment makers GE Healthcare(GE.N), Siemens (SIEGn.DE), Philips(PHG.AS) and Toshiba Medical Systems (6502.T), who are also working on making lower-radiation CT scanners.

"Doses are now in the 10 range," Raff said. "Within a couple of years, we are going to be seeing a lot of scanners with a dose of 1."

The research was supported by a grant from Blue Cross/Blue Shield of Michigan. Graff has done studies funded by Siemens, and Bayer AG BAYG.DE.

(Editing by Maggie Fox and Bill Trott)