CT, MRI rates vary widely, report shows

MRIexams are done half as often in Canadaas in the U.S., according to a new report, but it's not clear which isthe better approach.

The Canadian Institute of Health Information released its report Thursday on diagnostic tests performed in provinces as well as internationally. The report includes information such as variations in rates of CT exams.

The Canadian rate of CT exams was 121 per 1,000 people, compared with 228 per 1,000 in the U.S.The Canadian rate for MRI exams was 41 per 1,000 people, compared with 91 per 1,000 in the U.S.

Among OECD countries, Canada was in the middle of the pack for both exams. CT rates varied from a low of 60 in the Netherlands to a high of 321 in Greece. MRI rates varied from a low of 13 in Korea to a high of 98 in Greece.

"What we don't have at this point in time is a standard, a best practice to say this is how many exams should be done, or this is how much equipment you should have," said Francine Anne Roy, director of health spending and clinical registries at the Canadian Institute for Health Information in Toronto.

Medical imaging has helped detect disease in its early stages to save lives, Roy said.

But researchers in Canada estimatethat between 10 and 20 per cent of CT scansmake no contribution to patient diagnosis or management and may increase risks from radiation exposure.

For example, the radiation from a chest CT scan is 100 times greater than a chest X-ray.

Children face the biggest risks,since theyare smaller than adults,their organs are large in relation to their body as a whole, and their cells are multiplying, said Dr. Mark Greenberg, senior staff oncologist at Toronto's Hospital for Sick Children.

Evenincidental radiation from diagnostic tests carries a risk of damaging DNA in children, Greenberg said.

"Does it contribute to the occurence of subsequent cancers?"Greenberg asked. "Yes,I think the statistical data suggests it does, but that incremental risk is very small."

Reducing exposure

Research is underway in Canada and elsewhere to track how much radiation patients of all agesreceive from medical tests and treatments, whichwould helpminimize the risk of overexposure and cancer. In Canada, the effort is being built around electronic patient records, which are not yet in widespread use.

In the meantime, health professionalsin Canadaareworking toreduceexposure, even if the images are less vivid.According to the Canadian Association of Medical Radiation Technologists, its members arereducing the radiation delivered bymachines.

"There's a lot of attentionbeing paid to trying to increase the degree of appropriateness," said Chuck Shields, CEO of the Canadian Association of Medical Radiation Technologists in Ottawa.

Doctors are using other types of diagnostic tests where possible, such asultrasounds and MRIs that don't use radiation, and focusing onthe organ of interest tolimitexposure, Greenberg said.

For their part, patientscan ask questions about a recommended test, andremind doctors what tests they've already had, while keeping in mind that diagnostic tests are potentially life-saving.