TORONTO -- A study looking at technology used for mammography has found that one type is less effective at detecting breast cancer than others.

The Cancer Care Ontario study found digital direct radiography and screen film mammograms are better than digital computed radiography mammograms at uncovering breast tumours.

The research concluded that computed radiography, or CR, is 21 per cent less effective at detecting breast cancer than digital radiography, or DR.

Ontario's Ministry of Health is spending $25 million to phase out all 76 CR devices in the province and replace them with DR technology in response to the study.

"The evidence was very clear that one particular technology wasn't as good as others," Health Minister Deb Matthews said Tuesday.

"So that's why we are removing them and replacing them with more effective technology."

Matthews said she wants to replace the equipment as quickly as possible, and the province has already put out a request for proposals.

"We've come a long, long way when it comes to our breast-screening program," she said. "We know that it's saving lives."

Cancer Care Ontario says the chance of undiagnosed cancer in women screened with mammography using CR is extremely low.

But the agency is asking mammography clinics to inform women last screened with that technology.

CR technology is used nationally and internationally, and currently accounts for 20 per cent of all mammography machines in Ontario.

The study of almost 690,000 women in the Ontario Breast Screening Program is published in the journal Radiology.