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One of the most recent advances in
x-ray mammography is digital mammography. Digital
(computerized) mammography is similar to standard mammography in that x-rays are used to
produce detailed images of the breast. Digital mammography uses essentially the same
mammography system as conventional mammography, but the system is equipped with a digital
receptor and a computer instead of a film cassette. Several studies have demonstrated that
digital mammography is at least as accurate as standard mammography.
Digital spot view mammography allows
faster and more accurate stereotactic biopsy. This results in shorter examination times
and significantly improved patient comfort and convenience since the time the patient must
remain still is much shorter. With digital spot-view mammography, images are acquired
digitally and displayed immediately on the system monitor. Spot-view digital systems have
been approved by the U.S. Food and Drug Administration (FDA) for use in guiding breast biopsy. Traditional stereotactic biopsy requires a mammogram
film be exposed, developed and then reviewed, greatly increasing the time before the
breast biopsy can be completed.
In addition to spot-view digital
mammography, the FDA has approved a "full-field" digital mammography
system to screen for and diagnose breast cancer. With continued improvements,
the "full-field" mammography systems may eventually replace traditional
mammography.
How Does
Digital Mammography Differ From Standard Mammography?
In standard mammography, images are
recorded on film using an x-ray cassette. The film is viewed by the radiologist using a
"light box" and then stored in a jacket in the facility’s archives. With
digital mammography, the breast image is captured using a special electronic x-ray
detector, which converts the image into a digital picture for review on a computer
monitor. The digital mammogram is then stored on a computer. With digital mammography, the
magnification, orientation, brightness, and contrast of the image may be altered after the
exam is completed to help the radiologist more clearly see certain areas.
To date, studies of digital mammography and standard film mammography have shown that digital mammography
is "comparable" to film mammography in terms of detecting breast cancer.
In a 2004 article published in the journal, Radiologic Clinics of North America Radiology, researchers admit that early
studies of digital mammography have been somewhat disappointing because they have not shown a
significant advantage over standard film mammography. However, the researchers reiterate that digital
mammography is in its infancy and can expect to improve more rapidly than standard film mammography.
Small studies have shown that digital mammography may provide additional benefits, such as lower radiation doses and higher
sensitivity to abnormalities. For example, a study reported in the March 2001 issue of Radiology
found that the use of digital mammography can lead to fewer "recalls" (repeat mammograms) than film
mammography. Other data from German researchers suggest that the radiation dose can be reduced by up to
50% with digital mammography and still detect breast cancer as well as the standard radiation dose of film
mammography. However, the radiation dose of standard film mammography is still extremely low and does not
pose a risk to women.
The largest U.S. federally-funded clinical trial on medical imaging is currently underway determine whether digital
mammography is equal or superior to standard film mammography in helping to detect breast cancer. The study,
called the Digital Mammographic Screening Trial (DMIST), is being coordinated by the American College of Radiology
Imaging Network. Nearly 50,000 women have been recruited to participate in several locations throughout the
United States. Preliminary results released in September 2005 show that digital mammography is not more accurate
for the majority of women. However, the study found that women with dense breasts, those who are pre- or
perimenopausal (women who had a last menstrual period within 12 months of their mammograms), or those who
are younger than age 50 may benefit from having a digital rather than a film mammogram. Further results are
expected as researchers continue to analyze the study's findings.
In a 2004 article published in the journal, Radiologic Clinics of North America Radiology, researchers admit
that early studies of digital mammography have been somewhat disappointing because they have not shown a significant
advantage over standard film mammography. However, the researchers reiterate that digital mammography is in its
infancy and can expect to improve more rapidly than standard film mammography. Small studies have shown that
digital mammography may provide additional benefits, such as lower radiation doses and higher sensitivity to
abnormalities. For example, a study reported in the March 2001 issue of Radiology found that the use of digital
mammography can lead to fewer "recalls" (repeat mammograms) than film mammography. Other data from German
researchers suggest that the radiation dose can be reduced by up to 50% with digital mammography and still
detect breast cancer as well as the standard radiation dose of film mammography. However, the radiation dose
of standard film mammography is still extremely low and does not pose a risk to women.
Digital mammography systems cost approximately 1.5 to 4 times as much as standard film mammography
systems. While procedural time saved by using digital mammography over standard film mammography justifies
part of the cost for facilities that perform several thousand mammograms each year, the study will determine
whether the high cost of digital mammography is justifiable in terms of its benefits in detecting breast cancer.
From the patient's perspective, a digital mammogram is the same as a standard film-based mammogram in that
breast compression and radiation are necessary to create clear images of the breast. The time needed to
position the patient is the same for each method. However, conventional film mammography requires several
minutes to develop the film while digital mammography provides the image on the computer monitor in less
than a minute after the exposure/data acquisition. Thus, digital mammography provides a shorter exam for
the woman and may possibly allow mammography facilities to conduct more mammograms in a day. Digital
mammography can also be manipulated to correct for under or over exposure after the exam is
completed, eliminating the need for some women to undergo repeat mammograms before leaving the facility.
With digital mammography, the magnification, orientation, brightness, and contrast of the mammogram image
may also be altered after the exam is completed to help the radiologist more clearly see certain areas of the breast.
In the near future, digital mammography may provide many benefits over standard film mammography. These benefits include:
- Improved contrast between dense and non-dense breast tissue
- Faster image acquisition (less than a minute)
- Shorter exam time (approximately half that of film-based mammography)
- Easier image storage
- Physician manipulation of breast images for more accurate detection of breast cancer
- Ability to correct under or over-exposure of films without having to repeat mammograms
- Transmittal of images over phone lines or a network for remote consultation with other physicians
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