Trillium Health Partners is reviewing 3,500 CT scans and mammograms for accuracy after a "performance issue" with a radiologist who worked at two Toronto-area hospitals.

The community-based acute-care facilities issued a statement Wednesday night that said patients that were part of the review had been notified by letter, and of those, 189 people had multiple scans.

CBC News was unable to confirm the total number of patients included in the review.

The tests in questions were conducted between April 1, 2012, and March 31, 2013, at the Mississauga Hospital and the Queensway Health Centre in Toronto.

The spokesperson said the radiologist had worked at the Trillium hospitals for 33 years and his "privileges" to provide diagnostic imaging were restricted as of April 1, 2013.

'We apologize for any concern the news of this review may cause and want our patients and community to know it is being done to ensure the highest quality of care at our hospital.'—Michelle DiEmanuele, Trillium Health Centre CEO

Trillium Health has launched an external review team, led by Dr. Brian Yemen, chief of diagnostic imaging, Juravinski Hospital and Cancer Centre and McMaster University Medical Centre at Hamilton Health Sciences.

"We apologize for any concern the news of this review may cause and want our patients and community to know it is being done to ensure the highest quality of care at our hospital", says Michelle DiEmanuele, president and CEO of Trillium Health.

Trillium Health said the findings of Yemen's review would be made public once complete, and "expanded as necessary" based on those independent recommendations.

The hospital has also said it will be following up directly with all patients as soon as their tests have been reviewed.

Trillium Health is made up of the Credit Valley Hospital, Mississauga Hospital, and Queensway Health Centre, and serves a population of 1.15 million people.