A discussion of conventional mammography
A mammogram is basically an x-ray image of the breast. Differences in breast tissue generally show as different shades of grey in the image.
Fat, being relatively radiolucent, appears as black on the film. ‘Radiolucent’ refers to anything that permits the penetration and passage of X-rays whereas ‘radiopaque’ refers to anything that blocks the penetration of X-rays.
Tumors will appear as shades of gray on mammography, whilst calcifications (microcalcifications) are white. Benign lesions are most often circumscribed and in regular contours, whilst tumors often appear as speculated masses (needle-like shapes).
Breast cancer specialists estimate that 30% to 50% of mammographic cancers appear as pleomorphic microcalcifications. So ‘pleomorphic’ means ‘having many different shapes’, with or without a mass or lump.
Mammography usually reveals about 85% of the breast content. But, what this means, is that the scan does not detect up to 15% of breast cancers. However, mammoram usually detects microcalcifications typical of malignant tissue.
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Mammography Views
Images from mammography are typically from two to four angles (or views).
So, let’s have a look at some views:-
So, ‘Cranial-Caudal’ (CC) is a view from above. while an oblique or angled view ‘mediolateral-oblique‘, or (MLO). The ‘medio-lateral view‘, (ML) is a view from the center of the chest outward, whilst the ‘latero-medial‘ view (or LM) is a view from the outer side of the breast, towards the middle of the chest.
Radiologists prefer the MLO view or ‘from the side-at an angle‘, view to a 90 degree projection. This is because the MLO view allows imaging of more of the breast in the upper-outer quadrant, and also the axilla (armpit area).
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. Also, the CC view also tends to clearly depict the nipple.
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) shows on mammogram as a narrow light band on about half of the picture. Again, imaging of the nipple is also clear 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
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 mammogram converts the x-ray image photos into an electrical charge, in turn the electrical charge becomes a digital value.
However, there are benefits to a digital result. Once data is digital specialists can import the data into all sorts of computer analytical filters and data banks. Thus, computer Aided Detection is likely to prove useful 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 the radiologist incorporates multiple views into the computer aided detection model, the sensitivity for breast cancer detection increases.
Breast MRI (magnetic resonance imaging) is used at times in mammography, but not as much as one might think. So, specialists believe MRI scanning gives the most detail and sensitive diagnostic scanning technology. However MRI scans have 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 to 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.
A few common Q&A’s on conventional mammography…
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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.
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How can mammograms be used?
A mammogram can be used either for screening or for diagnostic purposes.
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How often should you have a mammogram?
It all depends on your age and your risk of breast cancer.
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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.
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What are the risks?
Some known risks and limitations of mammograms include the following: Mammograms expose you to low-dose radiation. Mammograms are not always accurate. Also, they can be difficult to interpret in younger women. Having a mammogram may lead to additional testing. Screening mammography can not detect all cancers, and not all of tumors found by mammography can be cured.
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How do I prepare for my mammogram appointment?
Choose a certified mammogram facility. Always try to schedule the test for a time when your breasts are least likely to be tender. Remember to bring your prior mammogram images. Do not use deodorant before your mammogram. Finally, consider an over-the-counter pain medication if you find that having a mammogram is uncomfortable.
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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 have appeared since your last mammogram.
References
- Baxi SS, Snow JG, Liberman L, Elin E. (2010) The Future of Mammography: Radiology Residents’ Experiences, Attitudes, and Opinions. Am J Roentgenol (2010) ;194(6):1680-1686. https://www.ncbi.nlm.nih.gov/pubmed/20489113
- Bassett LW, Monsees BS, Smith RA, (et al). (2003) Survey of radiology residents: breast imaging training and attitudes. Radiology 2003; 227:862–869 https://www.ncbi.nlm.nih.gov/pubmed/12728182
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