TORONTO - Wait times for MRI and CT scans in Ontario could be reduced by cutting back on unnecessary scans ordered by doctors, a new study suggests.

The work -- an analysis of why scans were ordered and what treatment course was followed -- suggests more rational use of the available machines should be considered.

"One way of reducing wait times is to not order scans in patients who are unlikely to benefit from them,'' lead author Dr. John You said in a release issued by Toronto's Institute of Clinical Evaluative Sciences, where he and his colleagues did the work.

"If we can reduce inappropriate use, then we can improve access to CT and MRI scans for those who will benefit.''

Among the study's findings was the fact that MRI use is higher for patients who live in high-income neighbourhoods, even though it's well known that people on low incomes tend to have more health problems than the wealthy.

"Although Ontario has a single-payer health-care system that strives to provide universal access to care, our findings suggest that access to MRI may be influenced by factors other than clinical need alone,'' said the study, published in the June issue of the Canadian Association of Radiologists Journal.

Cutting wait times for imaging tests is one of the priorities set by the 2004 wait time accord between the provinces and the federal government.

In Ontario the number of CT scanners has increased four-fold and the number of MRI scanners increased 12-fold between 1993 and 2006. Currently, the estimated wait for a CT scan is 5.5 weeks and 14 weeks for an MRI scan.

The work was funded by the Ontario Ministry of Health and Long-term Care's Ontario Wait Time Strategy. You, the lead author, is a scientist with the Institute for Clinical Evaluative Sciences and an assistant professor of medicine and clinical epidemiology and biostatistics at McMaster University in Hamilton.

For the study, the researchers selected a random sample of 20 Ontario hospitals performing CT scans and 20 performing MRIs.

They then looked at chart data for roughly 200 scans for each of the three anatomical regions -- abdomen-pelvis, brain or chest for CT scans and brain, spine or extremities for MRIs -- studying the reason given for ordering the scan, the finding and the recommended course of treatment.

In total, they studied data from 11,824 CT scans and 11,867 MRIs performed after Jan. 1, 2005.

They found that while CT scans of the brain were most commonly ordered for headaches, less than two per cent of those scans revealed a treatable abnormality.

"Although negative scans certainly have value in ruling out disease, many patients with a very low pre-test probability of disease can be reassured without performing a scan,'' the study suggested.

And while 90 per cent of MRIs of the spine showed abnormal results, it is not clear how clinically important most of those abnormalities were, the study said.

One in four CT scans of the abdomen-pelvis and of the chest resulted in a recommendation for further testing, a fact the authors said belies the commonly held notion that an imaging test will lead to a definitive diagnosis.

The authors noted that while doctors often justify ordering scans by saying patients demand them, those patients might feel differently if they realized there was a real likelihood that an answer wouldn't be found and additional, possibly invasive tests might be ordered as a followup.

Given how much the province has invested in additional CT and MRI scanning equipment since 2005, it's important to assess how well the machines are being used, the authors said.

They suggested the province should develop a web-based ordering system that would capture, in real time, the reasons why imaging tests are ordered and test results. Such a system would make it easier to audit the appropriateness of ordering patterns, they said.