ATLANTA (AP) — A long-awaited federal study of an X-ray alternative to the dreaded colonoscopy confirms its effectiveness at spotting most cancers, although it was far from perfect.

Medicare is already considering paying for this cheaper, less intrusive option that could persuade more people to get screened for colon cancer. And some experts believe the new method may boost the 50 percent screening rate for a cancer that is the country’s second biggest killer.

“We’re talking about for the first time really screening the population,” said Dr. Carl Jaffe, an imaging expert at the National Cancer Institute who was not involved in the research.

In the new study, the largest of its kind, the so-called “virtual colonoscopy” identified nine out of 10 people who had cancers and large growths seen by regular colonoscopies.

But there were flaws, too. Among them: The radiologists sometimes misread the X-ray, leading them to spot polyps that weren’t there. That led to unnecessary follow-up testing.