Upcoming Multicenter Study Will Compare Digital Versus Film Screen Mammography

CHICAGO--Although digital whole breast mammography has a number of possibleadvantages over conventional mammography, including enhanced image contrastand better exposure of dense tissues, it is not yet known whether the technologywill be equal to or better than conventional film screen mammography indetecting breast cancer, Stephen A. Feig, MD, said at the RadiologicalSociety of North America (RSNA) annual meeting.

Dr. Feig, director of the Breast Imaging Center, Thomas Jefferson UniversityMedical Center, Philadelphia, has been evaluating a whole breast digitalmam-mography unit that scans the breast transversely using a slot-shapedbeam covering an 18 × 24 cm area and providing resolution at approximately10 line pairs per millimeter (see Figure1 and Figure 2 ).

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

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

Digital mammography nevertheless may prove to be as sensitive as filmscreen mammography to the presence of breast cancer. "The reason isthat digital mam-mography has better contrast and better exposed imageswith less detector noise," Dr. Feig added.

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

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

Digital Work Stations

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

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

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