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What's the difference between screening and diagnostic imaging?

Medical imaging helps patients better understand their health by taking a detailed look inside the body; something Mayfair Diagnostics has been helping Calgary patients with for more than 100 years.

Medical imaging usually falls into two categories: diagnostic imaging or preventative screening.

Diagnostic imaging is often requested to investigate a specific concern, either to identify a cause for symptoms or if a doctor has discovered an abnormality. For example, it could be an X-ray to identify whether or not a bone is broken, an obstetrical ultrasound to confirm a pregnancy, a mammogram to check a lump for breast cancer, or even a Computed Tomography (CT) scan to investigate the presence and extent of heart disease.

Preventative screening uses the same imaging types as diagnostic imaging, but often without specific symptoms or concerns. It can be used to help detect diseases before they cause symptoms and while they can still be successfully treated.

“Some patients are at high risk of serious illnesses like heart disease, colon cancer, or lung cancer due to a family history of disease or other risk factors. In their cases, preventative CT screening may be beneficial to help detect early signs of these diseases,” says Dr. Sarah Koles, lead radiologist at Mayfair Diagnostics.

Another good example of the benefits of screening is breast cancer screening with mammography. While diagnostic mammography is used on both women and men to investigate a new concern like new pain, nipple discharge, or a concerning lump, screening mammography can be requested for women aged 40 and above when there are no symptoms, as part of a breast screening program. Mammography is a type of X-ray exam that takes images – called mammograms – for a detailed look at the internal structure of breast tissue to see changes that are too small for you or your doctor to feel. Having a screening mammogram every year, or every two years, makes it easier for a radiologist to compare your images and see changes or areas of concern.

Breast cancer will affect one in eight women in Canada, but if you find it early, there is less chance of recurrence and an increased chance that it has not spread to the lymph nodes, so the odds are better you will survive it. Thanks to preventative screening more women are surviving a breast cancer diagnosis. In 2017, 87% of women diagnosed with breast cancer were still alive after five years.

Early detection is also important for heart disease, lung cancer, colon cancer, and many other serious illnesses. For example, the 2018 results of the NELSON trial in Belgium and the Netherlands concluded that CT screening of asymptomatic men at high risk for lung cancer reduced lung cancer deaths by an overall percentage of 26% after 10 years. Read this article for more about this study.


Preventative screening could include a variety of tests. There are prostate-specific antigen blood tests to help detect prostate cancer, stool tests to help detect colon cancer, Pap tests to help detect cervical cancer, and more. In terms of medical imaging, some preventative screening tests are covered under provincial health care plans, like mammography exams for breast cancer screening and bone mineral densitometry exams to look for osteoporosis. At Mayfair Diagnostics the majority of our services are available through the Alberta or Saskatchewan health care insurance plans, but we do offer private CT and MRI services as a compliment to the public health care system. These include private screening exams, such as a Virtual Colonoscopy or low-dose screening chest CT to look for early signs of cancer, or a Coronary CT Angiography to assess your individual risk of heart disease. These exams are available as private pay exams.

Both preventative screening and diagnostic imaging exams must be requested by your health care practitioner. To determine which type of imaging is recommended, you and your doctor might discuss your medical and family history, risk factors, symptoms (if any), etc.

For more information on preventative or diagnostics imaging exams, please visit our services page.


Canadian Cancer Society (2018) “Breast Cancer Statistics.” Accessed October 17, 2018.

Engmann et al. (2017) “Population-Attributable Risk Proportion of Clinical Risk Factors for Breast Cancer.”  JAMA Oncology. 2017; 3(9) 1228-36.

IASLC 19thWorld Lung Conference on Lung Cancer. NELSON Study Shows CT Screening for Nodule Volume Management Reduces Lung Cancer Mortality by 26 Percent in Men. Press Release. September 25, 2018.

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