Excerpt from Mammography - Computer-Aided Detection

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Computer-aided detection (CAD) for mammography is a new and evolving topic in the realm of breast radiology. Despite our best efforts, radiologists have long known that some breast cancers remain undetected on screening mammograms. As the public grew more aware of this problem, medical/legal aspects of mammographically missed breast cancers became a pressing issue for both radiologists and lawyers.

A variety of reasons may explain why breast cancer is missed on mammograms. Some breast cancers simply are not seen on mammograms and may remain hidden by dense tissue until a lump is felt. Other cancers are difficult to see because they blend into the background of fibroglandular tissue and are overlooked at screening. On retrospective evaluation, these cancers are occasionally detected; however, they might be missed a second time. Still other cancers are located in areas difficult to visualize (eg, subtle calcifications on the burned-out edge of the image). Occasionally, cancers are missed for no other reason than momentary distraction or inattention of the screening radiologist.

Reasons for false-negative findings on mammography are difficult to determine because months to a year may pass before the cancer is detected, by which time it may have progressed to a more advanced state. Unfortunately, negative mammograms do not guarantee the absence of cancer, despite the wishes of both doctors and patients.

As a result, years ago researchers began to develop better methods to make lesions more conspicuous on mammograms. Film and screen technology improved, quality standards were enacted, and breast radiology progressively became a more specialized field, allowing some radiologists to focus primarily in that area. Nevertheless, false-negative rates in mammography remain too high (Burhenne et al, 2000). Therefore, computers and CAD were applied to help detect breast cancer at an earlier stage. For CAD to be effective, it must be used widely. CAD can achieve its greatest contribution to medicine in the field of breast cancer, where it can help radiologists to detect cancers at the earliest stages possible. It is in this stage when most mammograms are read and most cancers missed.

CAD is no longer a new modality. The US Food and Drug Administration (FDA) approved the first CAD system as an aid to the radiologist in screening mammography in June of 1998. As of 2001, only 130 CAD units were in clinical operation in the United States, many in academic centers. Now, more than 1600 units are being used in active clinical practice, and many new vendors have entered the CAD arena.

Still, the concept of computers reading mammograms has been received with mixed feelings in the radiology community. The primary authors' personal experience in giving lectures is that many radiologists are afraid of the technology. For radiologists to accept CAD, they may need a better understanding of what it is, how it works, and how to use it in the everyday environment of breast radiology.

Regarding nomenclature, CAD stands for computer-aided detection. In its present form, CAD should be used only for detection and never for diagnosis or reassurance. Regrettably, the erroneous term computer-aided diagnosis has been written into the lay and radiologic literature.

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