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What is a Mammogram?

Mammograms are x-rays of the breasts completed in privacy by a specially-trained female technologist. 

A screening mammogram consists of four images (two of each breast) that look for hidden cancer in women who are healthy (no symptoms) and have never had breast cancer. 

Those experiencing symptoms including a lump or nipple discharge should see their doctor immediately to determine if other testing is required.

For more information about mammography, watch the animated video below.


Video available in EnglishCantoneseMandarin & Punjabi

What happens during a mammogram?


Video available in EnglishCantoneseMandarin & Punjabi


A female medical radiation technologist will place your breast on a special x-ray machine.


A plastic plate will be used to hold your breast in place for a few seconds.


You will feel some pressure on your breast during the x-ray. Compression is necessary to spread the breast tissue and eliminate motion, which may blur the picture. This may be uncomfortable and usually lasts no more than 10 seconds.


Four pictures are taken, two of each breast.


The technologist will check the quality of the pictures to make sure the radiologist can read them. Then, if needed, the technologist may take additional pictures. 

Why do the breasts get compressed during a mammogram?


Video available in EnglishCantoneseMandarin & Punjabi

Why do women need regular mammograms?


Video available in EnglishCantoneseMandarin & Punjabi

How to prepare for your mammogram

  • Wear a two-piece outfit with a top that opens in the front. You will be asked to undress from the waist up.
  • Do not use deodorant, powder, creams or lotions on the day of the appointment. These products may leave a residue that can make it hard to read your mammogram.
  • Try to schedule an appointment when your breasts are least sensitive (within 10 days of your last period).
  • Some women also find it helpful to avoid caffeine several days before an exam.

Your questions

Body Mass Index (height and weight) has been recognized as a risk factor for breast cancer.  BC Cancer Breast Screening has begun to collect this information to assist in assessing an individual’s breast cancer risk so that it may guide screening accordingly.

How does this affect your appointment?
The technologist will ask if she may measure your height and weight before your mammogram which will be documented on your confidential history form.  

How long will this take?
It shouldn’t take more than a minute for the technologist to measure your height and weight.

Is this a required part of the screening mammogram?
We respect that agreeing to height and weight measurement is an individual decision, just as breast screening is, and it is in no way conditional to you having a screening mammogram. Please remember that all data that the screening program collects is completely confidential.

Where can you find more information about this?
BC Cancer Breast Screening collects personal information under the authority of the Health Act and section 26(c) of the Freedom of Information and Protection of Privacy Act (FIPPA). 

More information about reducing your risk can be found here.
BC Cancer Breast Screening doesn't recommend the use of thyroid guards for screening mammograms because they can interfere with capturing a clear breast image. The guard can limit the technologist’s ability to place all of the breast tissue on the compression plate. As a result some breast tissue may be missed or more x-rays may need to be taken. 

Also, the screening mammography x-ray directs the radiation beam towards the breast tissue, so the thyroid isn't directly exposed to the radiation beam. The thyroid can be exposed to "background scatter radiation”, which is the same amount of radiation a North American would be exposed to from 30 minutes of natural background radiation. 

Yes. You are welcome to bring someone for support in the waiting area and to help with the check-in process. It is best to let your technologist know if you have any concerns. She will work with you to make the test as comfortable as possible.


Screening mammograms can find most types of breast cancer early, but like all screening tests, they aren't perfect. Some cancers can't be seen on an x-ray and some cancers can develop quickly between 2 year intervals. Learn more about the benefits and limitations of screening mammography.


Screening mammograms are for women with no symptoms of breast cancer (no apparent breast problems). Diagnostic mammograms are ordered by a doctor to look at an area of concern in the breast; which may lead to more tests; such as an ultrasound or a biopsy.

The effectiveness of screening mammography has been well established by several large clinical trials across the world. These trials have found a relative risk reduction of breast cancer deaths of between 15-25% for women aged 50-69. Of eight randomized control trials for screening mammography, seven showed that screening mammography is beneficial.

In February 2014, the British Medical Journal published 25-year follow-up results from the Canadian National Breast Screening Study- the only randomized control trial suggesting that annual screening in women age 40-59 does not reduce breast cancer mortality beyond that of physical examination (for the 50-59 year olds) or usual care (for 40-49 year olds). BC Cancer does not agree with the findings in this study, and other credible evidence does not correlate with the findings.

Tomosynthesis is a new technology available to improve investigation of breast problems. The quality of all mammograms in the BC Cancer Breast Screening program is of the highest standard. Further assessment is needed to determine the optimal use of breast tomosynthesis in breast health. Until more information is available, the primary use of this technology will remain in the diagnostic setting.


SOURCE: What is a Mammogram? ( )
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