Dr. Ikeda is an Associate Professor in the Department of Radiology at Stanford University, Stanford, CA.

The CAD systems scan digitized film-screen mammograms, previously loaded into special digitizers by a technologist or technologist aide. Special computer algorithms search the digitized film-screen mammograms for abnormal findings and mark the findings on a low-resolution mammogram reproduction on paper or on a monitor. The marks alert the radiologist to focus on the findings to determine if they are possible masses or calcifications that require further work-up, namely recall from screening. The CAD programs are reproducible, tireless, and not distracted by the complexities of image interpretation that influence human beings. It was hoped that these CAD programs would aid radiologists in detecting small cancers, which otherwise may not have been perceived at the time of image interpretation.

This seemingly clear-cut case for using a computer to find small cancers is a complex issue, however. Although peer-reviewed scientific studies have shown that CAD programs can detect subtle but suspicious mammographic findings in dense or complex breast tissue, these studies also show that CAD programs do not detect every breast cancer. This means that the decision to recall a finding on a mammogram still rests solely on the radiologist's experience and judgement in film interpretation. Secondly, the types of CAD algorithms that search the mammograms vary from company to company, just as two radiologists may read the same mammogram on different receiver-operating curves, and the detection rates for each company have never been compared. Next, the psychological influence of the CAD program on a radiologist's decision to recall a finding has not been studied. How does the CAD program influence the radiologist's decision to recall a finding if it has not been marked? What are the implications of marks on findings that are "normal" structures? These issues regarding CAD's role and its influence on film interpretation will certainly be explored in greater detail over the next few years.

The other major concern regarding implementing CAD programs is its cost. Issues of reimbursement in this economically challenged medical environment influence whether institutions will purchase CAD equipment and whether the cost of running this program will be justified. From an economic point of view, the cost of the CAD equipment and personnel salaries to digitize the films and collate the CAD output with the screening mammograms all should be considered. Does purchase of a CAD program make economic sense?

This supplement covers these issues and explores new territories in which CAD is being used to evaluate mammograms in clinical practice. The articles review the scientific literature relating to methods of obtaining CAD output and to CAD's use in clinical practice for screening mammograms. The authors raise issues of reimbursement and examine the advantages and disadvantages of using CAD programs. These articles also answer the difficult questions of "What is CAD?" "How does CAD work?" and "What has the scientific literature shown regarding CAD and screening mammograms?" After reading this suppement, a radiologist may have a more informed answer to the important question, "Is CAD right for my practice right now?"