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Upcoming Multicenter Study Will Compare Digital Versus Film Screen Mammography

Upcoming Multicenter Study Will Compare Digital Versus Film Screen Mammography

CHICAGO--Although digital whole breast mammography has a number of possible advantages over conventional mammography, including enhanced image contrast and better exposure of dense tissues, it is not yet known whether the technology will be equal to or better than conventional film screen mammography in detecting breast cancer, Stephen A. Feig, MD, said at the Radiological Society of North America (RSNA) annual meeting.

Dr. Feig, director of the Breast Imaging Center, Thomas Jefferson University Medical Center, Philadelphia, has been evaluating a whole breast digital mam-mography unit that scans the breast transversely using a slot-shaped beam covering an 18 × 24 cm area and providing resolution at approximately 10 line pairs per millimeter (see Figure 1 and Figure 2 ).

When compared with conventional closed-screen mammography, the digital mammography unit has produced better contrast detail visualization of a breast phantom. "It is able to see smaller objects and objects that have less contrast," Dr. Feig said.

Although digital mammography offers better exposure of dense tissue than conventional mammography, as was seen in the first actual case of breast cancer detected by the device, it sacrifices sharpness. The current digital mammography unit achieves greater resolution than an earlier prototype machine, he said, but still does not approach that of conventional mammography.

Digital mammography nevertheless may prove to be as sensitive as film screen mammography to the presence of breast cancer. "The reason is that digital mam-mography has better contrast and better exposed images with less detector noise," Dr. Feig added.

An upcoming study that will evaluate film screen and digital mammog-raphy in 500 medical centers according to breast cancer detection criteria of the American College of Radiology should determine the sensitivity of digital breast imaging technology.

Said Dr. Feig: "If digital mammog-raphy doesn't demonstrate advantages over film screen mammography, there will be a failure to justify the increased costs of the units."

Digital Work Stations

Digital work stations themselves offer potential advantages, Dr. Feig noted. They allow the clinician to manipulate images by zooming in on specific sites, inverting images from black on white to white on black, altering the contrast, annotating particular areas of interest, magnifying images in the same areas of both the right and left breast simultaneously, and displaying either four-on-one or full-sized images on a screen.

By increasing exposure at the work station, some lesions may be better visualized in breasts of intermediate or high density. Although some of the subcutaneous tissue is lost in the process, the tissue can be recovered in a second image. In fact, Dr. Feig said, "we may need two images to visualize the entire breast well."

Digital technology also opens the door for picture archiving, computer-aided diagnosis and detection, and telemammography.

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