As deputy chief medical officer of the American Cancer Society, Lichtenfeld knew the tiny nodule probably wasn't dangerous and that new research has documented an increased risk of cancer from CT scans.

"The reality is, I thought the radiation dose from those follow-up scans represented more of a threat than the nodule," he said.

As physicians find new ways to use diagnostic imaging to discover and deal with disease, concern is growing about Americans' increased exposure to potentially cancer-causing radiation. Annual radiation doses from medical imaging have soared sevenfold since the early 1980s, according to a report last year from the National Council on Radiation Protection and Measurements.

Meanwhile, as many as 14,500 people may end up dying annually from radiation-induced cancers caused by CT scans, new research suggests.

Late last month, Congress held hearings on the subject, and medical equipment makers announced changes designed to help prevent patients from getting overly high radiation doses. A few weeks earlier, the Food and Drug Administration launched an effort to reduce unnecessary exposure to radiation from medical tests.

Scrutiny is focusing primarily on more than 70 million computerized tomography scans performed in the U.S. every year, up from 3 million in the early 1980s. The scans help doctors identify brain tumors, kidney stones, and obstructed bowels and have revolutionized medicine, virtually eliminating exploratory surgery and aiding millions of patients.

People often ask for the tests, and for some doctors they've become an important source of income. For most, they're an essential medical tool. "You can run a patient through in just a few minutes, get amazing information about what's going on inside their body, and they don't glow green — so why not?" said Dr. Steven Birnbaum, staff radiologist at Southern New Hampshire Medical Center.

Ionizing radiation is the reason; CT scans shower patients with far more of it than other diagnostic tests. For example, a routine head CT produces the same dose as 400 dental X-rays while the dose from a chest CT equals to more than 100 X-rays. That radiation can wreak havoc at the cellular level, breaking or altering DNA strands and causing mutations that spin out of control, generating cancers many years later.

Yet patients' exposure to radiation from diagnostic imaging exams isn't regulated, with the exception of mammography. By contrast, regulations limit U.S. workers to no more than 50 millisieverts of radiation a year from nuclear materials. Someone who gets multiple medical scans can easily exceed that level, said Fred Mettler, a professor of radiology at the University of New Mexico.

The risks were highlighted in a recent study in the Archives of Internal Medicine warning that 29,000 radiation-induced cancers — half of them deadly — could result from the CT scans performed in 2007 alone.

Two years earlier, Columbia University researchers suggested that up to 2 percent of new cancers in the coming decades could be attributable to radiation exposure from CT imaging.

These conclusions are far from universally accepted, however, as no study has directly shown that CT scans cause cancer. Instead, scientific understanding of the link between radiation and cancer is drawn largely from studies of survivors of the atomic bombs dropped in Japan, as well as studies on workplace exposure.

"All the numbers are based on models," said Dr. James Thrall, radiology chairman at Massachusetts General Hospital.

In a landmark 2005 review of the data, the National Academy of Sciences concluded that even "the smallest dose has the potential to cause a small increase in (cancer) risk to humans." But many experts insist that risks from individual imaging studies are exceedingly small and shouldn't frighten people away from necessary tests.

"The risk of death by drowning is greater than the risk of death from a cardiac or body CT exam," noted Cynthia McCollough, professor of radiological physics at the Mayo Clinic, in testimony before Congress.

The biggest problem, McCollough said, is that operators of CT machines often don't have adequate education or training and "have not kept up with the rapid developments in the technology." As a result, some patients may get higher-than-recommended radiation doses.

Also, most doctors are poorly educated about the radiation risks associated with medical imaging — two-thirds or more underestimate the doses, according to several studies. There is little standardization, and doses patients receive can vary by a factor of 13, according to a recent research report.

Though the American College of Radiology has created criteria for when imaging tests are medically appropriate, these aren't widely followed. Several studies find that as many as a third of CT scans probably aren't warranted because they don't answer a pressing medical question, because they duplicate earlier exams or for other reasons.

As an example, Dr. Edward Michals of the University of Illinois at Chicago Medical Center said many patients with lower back pain undergo CT scans even though these rarely yield valuable medical information.

Thrall said: "Someone who has a simple headache without other neurological signs is very unlikely to have a serious medical problem that could be discovered with a CT scan. And yet tens of thousands of people are scanned for headaches of this kind every year."

Responding to such concerns, the FDA may require equipment makers to display and record radiation doses from imaging scans and sound an alert when doses exceed certain thresholds. The agency also said it would work with groups around the country to standardize doses associated with various scans. Manufacturers, meanwhile, plan to create a registry to track patients' radiation exposure and expand reporting of radiation-related medical errors.

UIC Medical Center this year created a committee that will closely examine protocols for imaging patients. One new protocol has reduced radiation doses for CT coronary angiograms by 80 percent. At the University of Chicago Medical Center, radiologists interpreting scans now review the radiation doses administered to patients and add the information to medical records.

Congress is under pressure to increase oversight. Some experts say that, at minimum, all facilities providing diagnostic imaging should be accredited and standards should be set for medical staff who perform and interpret scans. The government will require accreditation for imaging centers serving Medicare patients starting in 2012.

Still, as long as doctors fear missing an important medical complication and being sued, practices are unlikely to change, said Dr. Leonard Berlin, vice chair of radiology at Skokie Hospital.

And some doctors who own scanning equipment have a financial stake in diagnostic imaging. Research shows that doctors who own machines perform two to seven times more imaging tests than those who don't, said Dr. Vijay Rao, chair of radiology at Thomas Jefferson University Hospital in Philadelphia.

Moreover, "the physicians who own this equipment and order the tests have generally had no training in radiology and little understanding of the complexities of radiation dosing" and its attendant health risks, Rao said. "For patients, this is absolutely the perfect storm."

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ASK YOUR DOCTOR

Experts say patients should not request an unnecessary imaging test just to be on the safe side. Nor should they let unwarranted fear scare them away from a test. Questions to ask:

Why have you suggested this test? What do you hope to learn?

Do you expect the results might change your medical recommendations? How?

Are there alternatives that involve less radiation exposure? Could an MRI or an ultrasound substitute?

What's the average radiation dose associated with this kind of test? How many times will I be scanned?

Is there a way to perform this test that involves fewer scans and less radiation exposure?

Are you keeping a record of my scans and my radiation exposure?

Do you have an ownership stake in the machines used to scan me? (This applies if the scan occurs in a doctor's office.)

Are the technicians licensed or certified? Do you have a quality assurance program for diagnostic imaging? Are the machines checked routinely?

Is the facility where the scan takes place accredited? Will an expert radiologist interpret the test?

Note: It's also important to tell doctors about scans received elsewhere. If possible, provide copies.