A radiologist’s guide to getting a mammogram

Mammogram machine

Dr. Ania Kielar, vice-president of the Canadian Association of Radiologists and vice-chair of the University of Toronto’s department of medical imaging, explains what a mammogram is and how it helps in the early detection of cancer.

What is a mammogram?
A mammogram is a screening test that uses X-rays to detect cancer. During the procedure, each breast is compressed between two plates, horizontally and then vertically, for about 10 to 15 seconds while images are taken. “They’re three-dimensional structures that we’re trying to make two-dimensional,” Dr. Kielar says. “We take two images of each breast so we can see it from the front and the side. If you see a picture head on, you can’t tell exactly what’s going on until you look sideways to see what it is you’re actually seeing.”

What does a mammogram show?
Mammograms produce black-and-white images that radiologists examine for signs of cancer. Dense objects, such as bones or tumours, appear white on an X-ray, while soft tissues, such as skin, fat and muscle, look grey. “It’s basically all these different shades of grey,” Dr. Kielar says. “A woman’s breasts can be very dense, so they appear all white like a snowstorm, or they can be almost all fat and look black. The ones that are all fat make it much easier to find cancer. Cancer has a sort of grey or white colour. If somebody has dense breast tissue then it’s already a background of white so it makes it really hard to find cancer.”

How long does a mammogram take?
“Only a few minutes,” Dr. Kielar says. “As long as it takes to squish a breast and take two pictures and then do the other breast.”

How can patients prepare for a mammogram?
Age guidelines vary for the procedure, so patients should talk to their doctor about when they need to start getting mammograms. While some feel age 50 is appropriate, most radiologists believe the process should begin 10 years earlier, at age 40, as younger women tend to get more aggressive cancers. Women who are still of menstrual age should avoiding booking the procedure just before their period as their breasts may be more sensitive.

If they are going for their first mammogram, they should also be aware that their likelihood for being called back for additional images is higher than after the second, third or fourth time. “We don’t want them to feel anxious if they get called back,” Dr. Kielar says. “We’re looking at subtle things in the breast and if you don’t have anything to compare it to we like to be safe rather than sorry. If there’s something concerning we’ll do a biopsy. But even if you’re having a biopsy there’s still a really good chance that it’s nothing, so women need to be aware of that.”

It’s important to remember that, according to the American Cancer Society, only about two to four screening mammograms out of 1,000 result in a cancer diagnosis. Our job is to try to find stuff early on and if we find something that’s looks a little bit different, we have to investigate it.”

Is there anything patients should do after a mammogram?
“They can go about their day,” Dr. Kielar says. “They just need to follow up with their family physician to make sure they get the results.”

Are there any concerns or risks that accompany a mammogram?
Mammograms are generally safe with any risks from the low levels of radiation outweighed by the benefits of the procedure.

How long does it take for results to come back?
Typically, two to three days.

Has the pandemic changed the way mammograms are performed?
Many mammography clinics were forced to close during the first wave of COVID-19 and again during the rise of the omicron variant. “Wait lists have gone up significantly,” Dr. Kielar says. “I don’t know how much they’ve caught up — it’s been tough.”


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