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X-rays, mammograms and computed tomography (CT) scans. They're common, often routine, tests that can help doctors identify disease, injury or determine a patient's best course of treatment.

But they also emit radiation, sometimes at potentially harmful levels, that may contribute to a person's chance of developing cancer.

To some, the risks are a necessary trade-off to being able to precisely and accurately detect disease, disorders or other health problems invisible to the naked eye.

Now, new efforts are being created, including a new federally-funded program, to help understand radiation risks and how to protect patients.

Although medical-imaging technology has been around for decades, the issue of radiation exposure has been heating up in recent months as new research raises questions about the possible health risks from mammograms and other scans.

The use of such scans has spiked in the past decade, even among children, and many experts say an alarming number of tests are being given inappropriately. The Canadian Association of Radiologists estimates that up to 30 per cent of CT scans are inappropriate or contribute no useful information to help the patient.

As well, many doctors may not know a patient's history and how much radiation they have been exposed to in the past. Some tests may be assigned for conditions where a non-radiation-emitting alternative, such as an ultrasound, will do.

Efforts are under way to develop technology that may eventually be able to track radiation exposure in patients across the country. The National Research Council of Canada is launching a project with Agfa HealthCare Inc., Hamilton Health Sciences Corporation and McMaster University to create the country's first national radiation dose and exposure registry. Christian Couturier, director-general of the Institute for Information Technology at the NRCC, said the hope is that eventually, a patient's radiation exposure will be attached to his or her medical records, which can help doctors to limit a patient's radiation exposure by being more selective about assigning medical tests. He said they hope to commercialize the technology and sell it around the world.

Medical imaging allows doctors to see detailed pictures of the inside of the body, including moving pictures of organs while they work and three-dimensional images of deep tissue and organs. X-rays and other imaging tests may be used by dentists, chiropractors and other medical professionals in addition to doctors.

But the tests expose patients to ionizing radiation which has enough energy to displace electrons from an atom. In patients, that means radiation can enter cells and ionize, or create a positive charge, in a group of molecules that were previously neutral. Ionized molecules can then damage surrounding tissues, for example, leading to mutations in DNA. Those mutations could eventually lead to cancer.

A 2007 study published in the New England Journal of Medicine concluded that up to two per cent of all cancers could be attributed to radiation exposure from CT scans, which expose patients to much higher doses of radiation than X-rays. As a measure of the difference, a single CT scan of the chest is the equivalent of 400 chest X-rays.

Not all medical imaging procedures involve radiation. For instance, ultrasounds and magnetic resonance imaging don't expose patients to ionizing radiation and are seen by those concerned about radiation exposure as good alternatives in many situations.

“I think [patients] need to be made aware of these risks,” said Mark Baerlocher, a radiology resident at University of Toronto. “By far, the majority aren't aware of the risks and I think that's a problem.”

To help educate patients, Dr. Baerlocher and his computer-programming brother Adrian Baerlocher have developed an iPhone application that can help people track their exposure to radiation. Dubbed the “Radiation Passport,” the application allows users to input past scans or future medical appointments to determine their accumulated the level of radiation exposure.

One of the challenges is that exposure can also vary depending on the age of the machine – older ones likely emit more radiation – and the way machines are set up. It's also difficult to draw conclusive links between radiation and cancer, since it can take years to develop.

In an recent editorial in the NEJM, Michael Lauer, director of the division of cardiovascular sciences at the Maryland-based National Heart, Lung and Blood Institute, said radiation risks can't be ignored. One of the most troubling aspects of the debate, Dr. Lauer said, is that while medical imaging has revolutionized patient care in many ways, such tests are now used in a wide variety of situations that may not actually bring benefit to the patient.

He pointed to a study published in the Journal of the American Medical Association earlier this year that looked at whether people with Type 2 diabetes who were screened for coronary artery disease had a decreased incidence of heart attack or cardiac-related death. Despite the myocardial perfusion imaging screening test, the study found no difference in the health outcomes for patients in either group.

“It points out that just because a test can diagnose disease does not necessarily mean its use will lead to an improvement in health,” Dr. Lauer said in an interview.

Assessing the risks

Radiologists are working on ways to ensure tests use the lowest dose possible, said Ted Lyons, president of the Canadian Association of Radiologists. But CT scans and repeats of other medical tests could expose patients to harmful levels of radiation. As well, infants and children are about 10 times more sensitive than adults. The association offers the following guidelines:

– Ask your doctor if a test that doesn't use radiation may be just as effective.

– Parents should avoid allowing their child to have multiple scans.

– Ask for the lowest radiation dose possible for a child's test and ensure exposure is limited to the area being tested.

– Ask whether the facility is using reduced-radiation techniques.

– If the scan is medically necessary, then the benefits outweigh any risks.