Mammography is a low-dose x-ray of the breast. The picture made during mammography is called a mammogram.
Why mammography is done
There are 2 types of mammography, which are done for different reasons.
Screening mammography
Screening mammography is used to screen women who do not have any symptoms of breast cancer. Both breasts are examined during a screening mammography.
Screening mammography can help find lumps or abnormal areas of breast tissue that may be too small to be felt by hand. It monitors changes to the breast over time, and helps to detect breast cancer at an early stage.
Diagnostic mammography
Diagnostic mammography is done to diagnose a breast problem, such as a lump or suspicious area. The problem may be found by the woman, during a clinical breast examination or screening mammography.
Diagnostic mammography is more thorough and takes a little longer than a screening mammography. It provides more detailed images and views of the breast taken from different angles. Diagnostic mammography is usually done on both breasts so that doctors can compare the breast tissue of both breasts.
Diagnostic mammography may also be done to help find the abnormal area during a stereotactic core needle biopsy or wire localization biopsy.
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Preparing for mammography
The following preparations need to be done before mammography:
- Do not apply deodorant, antiperspirants, body lotion or talcum powder under the arms or on the breasts before mammography. These products can interfere with the accuracy of the x-ray.
- Wear clothing that is easy to remove from the waist up.
- Remove necklaces and other jewellery that might get in the way.
- The breasts may be tender 7–10 days before a menstrual period begins, so it may be helpful to avoid having mammography during this time.
- Avoiding drinks and food that contain caffeine, such as cola and chocolate, for 5–7 days before mammography may also help reduce discomfort.
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How mammography is done
Mammography is done in clinics on an outpatient basis.
- While a woman stands in front of the mammography machine, her breast is placed between 2 plastic compression plates.
- The plates are then pressed together to flatten the breast.
- Compressing the breast causes a certain amount of discomfort, but this only lasts a few seconds. If there is a lot of discomfort during the x-ray, tell the technologists. They may be able to adjust the compression.
- Compressing the breast tissue:
- increases the clearness of the mammogram
- helps show the internal structures of the breast
- allows less radiation to be used
- X-ray views of each breast are taken from different angles.
- Diagnostic mammography takes more views than screening mammography.
- The technologist will check the mammography films (mammograms) to make sure they are clear enough for the radiologist (a doctor who specializes in using imaging techniques) to read.
Spot compression
Spot compression (also called cone compression) may be used to provide special views of one area of the breast during diagnostic mammography.
- A small compression plate is used to separate the breast tissue in a suspicious area and push normal breast tissue out of the way, giving a clearer image.
- The images may be enlarged (magnified) to make it easier to see small suspicious areas. These close-up views help show tiny deposits of calcium (called calcifications) that look like small white spots on a mammogram. The radiologist looks at the size, shape and pattern of calcifications on a mammogram.
- Calcifications are quite common and most are not associated with cancer.
- Certain characteristics of calcifications, such as irregular shapes or certain groupings, can be a concern and may indicate the presence of cancer.
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What the results mean
The radiologist will read the mammogram to look for changes or abnormalities. Some mammography centres in Canada use the Breast Imaging Reporting and Data System (BI-RADS), which was developed by the American College of Radiology to report the results of the mammogram. Other centres may use a reporting system based on BI-RADS.
Breast Imaging Reporting and Data System (BI-RADS)
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Category 0 Assessment is incomplete | Additional mammogram images are needed, such as spot compression or ultrasound, or the images from an earlier mammogram are needed for comparison. |
Category 1 Negative | The mammogram is normal. There are no areas of concern found on the mammogram. Continue with regular screening mammograms. |
Category 2 Benign findings | The mammogram is normal, but there are abnormal areas that are benign based on their appearance on the mammogram. Continue with regular screening mammograms. |
Category 3 Probably benign | The mammogram shows an area that is probably benign, but a follow-up mammogram needs to be done in 6 months to watch for any changes to the area. Mammograms in this category mean that the abnormality has a less than 2% risk of being cancer. |
Category 4 Suspicious abnormality | The mammogram shows an area of concern. There is a 23%–34% chance that the abnormality is cancer. A biopsy is needed to make a diagnosis. |
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What happens if a change or abnormality is found
The doctor will decide if further tests are needed or not. Some tests that might be done include:
- diagnostic mammography – if an abnormality was found on a screening mammography
- breast ultrasound
- biopsy
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Breast implants
If a woman has breast implants, the technologist will take steps to make sure that as much breast tissue as possible is seen on the mammogram. Extra care is taken when compressing the breasts to avoid rupturing the implant.
- Special techniques (called implant displacement techniques) are used to move the implant out of the way and pull the breast tissue forward into the view.
- Additional views may need to be taken to ensure as much of the breast tissue as possible is examined.
- Studies show that women with breast implants are diagnosed with breast cancer at a similar stage and have a similar prognosis as women who do not have breast implants.
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Digital mammography
Digital mammography is a newer mammography technique. It is sometimes called full-field digital mammography.
Digital mammography is done the same way as standard film mammography. It takes an electronic image of the breast and stores it in a computer instead of putting it on x-ray film.
- Images can be enlarged or changed so they can be examined in more detail and can provide better views of suspicious looking areas.
- Images taken during digital mammography can be sent electronically from one location (such as a medical facility) to another and are easy to store.
- Digital mammography may be used to further examine an abnormality found during a screening mammography or to diagnose breast cancer in centres where this equipment is available.
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Mammography safety
Modern mammography equipment uses very low doses of radiation, but repeated exposure to x-rays does increase the risk of developing cancer. The benefits of mammography and finding breast cancer early outweigh the risk of repeated exposure to radiation.
Compressing the breast during mammography does not cause breast cancer. Even if a breast tumour is present, compression will not cause the tumour to grow or spread any faster.
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Limitations of mammography
Mammography does not find all breast cancers.
- A false-negative result means that the mammogram results are normal but the woman actually has cancer.
- A false-positive result means that the mammogram results indicate that a woman may have breast cancer when she really doesn’t. Further tests will show that many of these abnormalities are not cancer.
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