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.