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CT/MRI scan study suggests some tests are overprescribed


Ontario wait times have improved and this is attributed to the tens of millions of dollars pumped into healthcare by the province. But Ontarians continue to face long lineups for MRI and CT scans. We now have a much clearer picture on why people are waiting in some instances—doctors may be ordering tests when they are not really necessary.

Based on findings from Ontario’s Institute for Clinical Evaluative Sciences (ICES), scientists conclude that CT/MRI tests could be performed less often for some patients.” The focus of the Ontario Wait Times Strategy has been to spend nearly $100 million in the province to increase the supply of CT and MRI, yet despite this, wait times for MRI are still way above target. An obvious question is whether the scans are being ordered for the right and appropriate reasons,” says principal investigator and ICES scientist John You. “For the first time, this study puts a spotlight on why tests are ordered and how often they find abnormalities that will influence patient management. For many patients, CT and MRI scans are a crucial part of their care and they are waiting too long to get their tests. One way of reducing wait times is to not order scans in patients who are unlikely to benefit from them. If we can reduce inappropriate use, then we can improve access to CT and MRI scans for those who will benefit.”

The study of 11,824 outpatient CT scans and 11,867 outpatient MRI scans from randomly selected Ontario hospitals performed after January 1, 2005 found:

  • Headache was the most frequent indication for CT scans of the brain: less than two percent of these scans found treatable abnormalities that could explain the headache.
  • Back pain was the most common indication for MRI scans of the spine: 90% of these scans were abnormal, but the clinical importance of the abnormalities was unclear.
  • Over half of MRI scans of the extremities were for knee pain or suspected cartilage tear: 80% of these scans were abnormal, but the clinical importance of the abnormalities was unclear.
  • One in four CT abdomen/pelvis and CT chest reports recommend more testing.
  • More MRI scans were performed on patients living in high-income neighbourhoods than in low-income neighbourhoods, suggesting that access to MRI may be influenced by factors other than clinical need alone. No neighbourhood income trend was seen for CT scans.
  • Family physicians ordered the greatest number of scans, compared to other physician types. Cancer-related indications accounted for over 50% of CTs of the abdomen/pelvis and chest.

“As doctors, we sometimes get a bit defensive about the appropriateness of our own ordering patterns,” says You, staff physician at McMaster University. “One group of physicians will tend to point fingers at another as the source of the problem. But in reality, the onus doesn’t fall on one single group, and all of us—physicians, patients, researchers and government—must each play a role in improving the system.”

In the province of Ontario, the number of CT scans increased four-fold and the number of MRI scans increased 12-fold between 1993 and 2006. Currently, the reported wait times are 5.5 weeks for a CT scan and 14 weeks for an MRI scan, defined as the time by which 90% of patients have had their scans.

Possible ways of decreasing inappropriate use:

  • Better decision support using e-health solutions, developing web-based systems of ordering CT and MRI that incorporate current practice guidelines.
  • Tracking ordering patterns in real-time would allow feedback to clinicians, their peers and practice guidelines.
  • Educating physicians and the public about the pros and cons of diagnostic imaging is crucial. They must understand that diagnostic imaging tests are not perfect, they do not always provide a final diagnosis, can cause unnecessary anxiety and complications from biopsies when abnormalities turn out to be false alarm positives or ‘red herrings,’ and CT scans expose patients to radiation.

The study “Indications for and results of outpatient computed tomography and magnetic resonance imaging in Ontario” is in the June issue of Association of Radiologists Journal.

Author affiliations: ICES (Drs. You, Laupacis, Ms. Rothwell, Mssrs. Purdy, Przybysz, Fang); McMaster University (Dr. You); Keenan Research Centre, Li Ka Shing Knowledge Institute of St. Michael’s Hospital (Dr. Laupacis), Ontario.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.



  • Kristine Galka
  • Media Advisor, ICES
  • 416-480-4780 or 416-629-8493

Read the Journal Article