A discussion of conventional mammography
A mammogram is basically an x-ray image of the breast. Differences in breast tissue are generally revealed as different shades of gray on the image.
Fat, being relatively radiolucent, appears as black on the film. (Anything that permits the penetration and passage of X-rays is called ‘radiolucent‘, while anything which blocks the penetration of X-rays is called ‘radiopaque‘).
Tumors will appear as shades of gray while calcifications (microcalcifications) are white. Benign lesions are most often circumscribed and in regular contours, while tumors often appear as speculated masses (needle-like shapes).
It is estimated that 30-50% of mammographic cancers appear as pleomorphic microcalcifications (pleomorphic means ‘having many different shapes), with or without an associated mass or lump.
Mammograms usually reveal about 85% of the breast content, which means that up to 15% of breast cancers may be undetected by the scan. But, the microcalcifications which are typical of malignant tissue are usually detected.
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Mammogram image views
Mammograms are typically taken from two to four angles (or views). A view from above is called a ‘Cranial-Caudal‘ view, abbreviated CC, while an oblique or angled view is called ‘mediolateral-oblique‘, or MLO. The ‘medio-lateral view‘, abbreviated ML is taken from the center of the chest outward, while the ‘latero-medial‘ view or LM is taken from the outer side of the breast, towards the middle of the chest.
The MLO view or ‘from the side-at an angle‘, is preferred to a 90 degree projection because more of the breast in the upper-outer quadrant, and also the axilla (armpit area), can be imaged.
With the top-down or Cranial Caudal (CC) view, the entire breast is depicted. Fat tissue closest to the breast muscle should appear as a dark strip on the X-ray. The nipple is also usually clearly depicted.
The Mediolateral (or ML) view is very important because the lateral side of the breast is probably the most common place for pathological changes to occur. The view from the center of the chest, outward to the side, (ML) gives the best view of the lateral side of the breast. In this view the chest muscle (pectoral) is depicted as a narrow light band on about half of the picture. The nipple is depicted in profile.
With the Latero-Medial view (LM) the breast is X-rayed from the side towards the middle, and this gives the best view of the medial (mid-body) side of the breast.
|Cranial Caudal (CC) view of breast||Medio-lateral (ML ) view of breast||Medio-lateral-oblique (MLO) view of breast|
Digital mammography is starting to be used, but it is not yet clear as to whether the digital image reveals more than a conventional analog x-ray. In digital mammography, the x-ray image photos are converted into an electrical charge, which is then converted to a digital value. But there are benefits to a digital result- once data is digital it may be imported into all sorts of computer-related analytical filters and data banks. Computer Aided Detection will likely be used alongside a conventional human interpretation, to ensure the most accurate and informative reading.
Computer aided detection systems have proven to be a useful ‘second opinion‘ in interpreting mammograms, but have not proven to be as reliable and accurate as experienced radiologists. Computer aided breast cancer detection models tend to result in a higher ‘recall‘ rate, with little to no effect on the positive predictive value for biopsy. However, if multiple view’s are incorporated into the computer aided detection model, the sensitivity for breast cancer detection has been shown to increase.
Breast MRI (magnetic resonance imaging) is used at times in mammography, but not as much as one might think. While thought to be the most detailed and sensitive diagnostic scanning technology, it has it’s limitations as well. MRI is very expensive, with the results open to a more variable interpretation.
Conventional mammography saves lives, and is here to stay
Screening mammography has proven to be a beneficial and life saving technique, which may reduce mortality from breast cancer by up to 35% in women 50–69 years of age, and up to 20% in women in their 40’s. Even with the advent of computer aided detection systems and breast MRI, conventional mammography is sure to serve the purpose of early breast cancer detection and saving lives for years to come.
Let’s do a few common Q&A on conventional mammography…
- How are mammograms done? During a mammogram, your breasts are compressed between two firm surfaces to spread out the breast tissue. Then, an x-ray captures black and white images of your breasts that are displayed on a computer screen and examined by a doctor who looks for signs of cancer.
- How can mammograms be used? A mammogram can be used either for screening or for diagnostic purposes.
- How often should you have a mammogram? It all depends on your age and your risk of breast cancer.
- How do I know when I should begin screening mammography? Some general guidelines for when to begin screening mammography include women with an average risk of breast cancer and woman with a high risk of breast cancer.
- What are the risks? Some known risks and limitations of mammograms include the following: Mammograms expose you to low-dose radiation, they aren’t always accurate, they can be difficult to interpret in younger women, having a mammogram may lead to additional testing, screening mammography can’t detect all cancers, and not all of the tumors are found by mammography can be cured.
- How do I prepare for my mammogram appointment? Choose a certified mammogram facility, schedule the test for a time when your breasts are least likely to be tender, bring your prior mammogram images, don’t use deodorant before your mammogram, and consider an over-the-counter pain medication if you find that having a mammogram is uncomfortable.
- What can a radiologist possibly find on my mammogram imaging? Possible findings include calcium deposits, masses or lumps, distorted tissues, dense areas appearing in only one breast or one specific area on the mammogram, and new dense area that has appeared since your last mammogram.
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