How is a mammographic exam performed?

Updated: Jan 31, 2017
  • Author: Muhammad Neaman Siddique, MBBS; Chief Editor: Eugene C Lin, MD  more...
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Answer

Routine mammogram comprises of CC and MLO views. Adequate degree of breast compression is applied before shooting the X-rays. This helps in increasing the image contrast by reducing motion artifact and by enhancing the X-ray penetration. Acquiring 2 views is imperative in order to adequately image the whole breast tissue. Besides this, two views help in distinguishing a true abnormality from an overlapping structure. Studies have clearly established higher sensitivity and lower recall rates with 2 views. This benefit is generally believed to outweigh the risk associated with extra radiation from the second view.

The radiation dose absorbed by the breast depends on breast tissue thickness, increasing with the thickness of the breast. American College of Radiology recommends that the mean radiation dose exposure in a breast tissue measuring 4.2 cm should not exceed 0.3 rads per image. If accounted for the relative sensitivity of breast tissue to radiation exposure, the effective radiation dose received by the breast during a routine screening examination comes out to be approximately equivalent to the natural background radiation exposure cumulatively acquired over a 3-month period (ie, 0.7millisievert units). Women who have BRCA1 or BRCA2 mutation and thus have impaired DNA repair mechanisms are at increased risk for radiation-induced carcinogenesis as compared to women who do not have these mutations. However, keeping the radiation dose as low as possible in all women is important.

A digital mammography system tends to require a lower radiation dose than film screen mammography for the same image quality. Digital detector converts the X-ray photons to an electronic signal, which is further processed and displayed as a gray scale image. This image can either be electronically sent to a viewing station and displayed on a high-resolution monitor or printed and read on luminant-view boxes similar to how the film screen mammograms are read.

The digital system provides greater contrast resolution and thus better visualization of skin, peripheral breast tissue, and dense breasts. Besides this, it allows for changes in zoom, contrast, and brightness, which increase the ability to detect subtle abnormalities.

A film screen system does not offer such facilities and also tends to suffer from artifacts during processing and storage. These deficiencies are, however, partly compensated for by the advantage of a higher spatial resolution in film screens as compared to digital systems. However, despite of all these technological differences, studies have shown that the overall diagnostic accuracy was similar with these 2 modalities except for premenopausal and perimenopausal women in whom digital mammography was found to be more accurate. [12] This is at least partly because digital mammography is relatively more sensitive than film mammography in detecting cancer in dense breasts.


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