situ, treatment decisions can be difficult to make because so littleis known about the malignant potential of these premalignant cells.As a result, some women may face the diagnosis of breast cancer andthe subsequent therapy for a lesion that may never have become alethal, metastatic cancer. These issues are revisited frequentlyin the workshop summary.
Digital mammography consists of a dedicated electronic detector systemthat captures and displays the x-ray signals on a computer ratherthan film. Full-field digital mammography (FFDM) offers new capabilitiesnot provided by conventional film-screen mammography, according toCarl D'Orsi, who described the current status of development of diagnosticfull-field digital mammography. Unlike film-screen mammography, full-fielddigital mammography offers an infinite ability to manipulate contrastand brightness with one exposure. Many investigators in this fieldconsider such flexibility as a critical advance in helping to reducefalse negatives, which are most likely to occur when imaging densebreast tissue. Without the ability to adjust contrast and brightness,dense tissue can obscure precancerous and cancerous lesions.
Digital mammography separates the process of image acquisition fromthat of image display. The detector responds to x-ray exposure andthen sends an electronic signal for each pixel to a computer whereit is digitized, processed, and stored. Because the signal for eachpixel is digitally stored, the same image can be manipulated to showdifferent brightness and contrast combinations, allowing radiologiststo more easily see through denser tissues.
Digital mammography examinations can be displayed in either hardcopy(laser-printed film) or on screen (using a Cathode Ray Tube (CRT)monitor). With hard copy display, spatial resolution and gray scalerange are comparable to standard film screen mammography. However,laser-printed film is costly, involving significant costs for printing,development, personnel, supplies, and printing more than one versionof the mammogram.
With screen display (also known as softcopy), digital mammographycan be used for computer-aided diagnosis, using algorithms similarto those available for reading film screen mammography. A potentialadvantage of softcopy display over conventional film-screen mammographyis that it permits adjustment of magnification, brightness, and contrastafter the mammography examination, thus enabling a more detailedexamination of questionable areas without necessarily requiring additionalimaging.
Other potential benefits are its ease of image retrieval and transmission;ability to work in tandem with computer aided detection, and digitaltomosynthesis, a process whereby digitized images of the breast takenat different angles are used to reconstruct a three-dimensional imageor hologram of the breast. Studies on the feasibility of satellitetransmission of digital mammography, or telemammography, are alsocurrently underway.
A major limitation, however, is that spatial resolution and luminancerange—even with the most advanced CRT technology—is significantly lower than conventional film screen mammography.The speakers suggested that reading softcopy off a CRT display ultimatelywill prove unattractive to users. Instead, they envision using atechnology that involves liquid crystal displays similar to thoseon laptops because they are likely to provide better image quality.However, an
Based on presentations by Carl D'Orsi and Etta Pisano.