- How Does Digital Mammography Differ From Standard Mammography?
- Promising Developments in Digital Mammography
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.
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
As stated earlier, preliminary results of the Digital Mammographic Screening Trial (DMIST), released in September 2005, show that digital mammography may be more accurate at detecting breast cancer in some women than standard film mammography. According to the study results, digital and standard film mammography had similar accuracy rates for many women. However, digital mammography was significantly better at screening women in any of the following categories:
- under age 50, regardless of what level of breast tissue density they had
- of any age with very dense or extremely dense breasts
- pre- or perimenopausal women of any age (defined as women who had a last menstrual period within 12 months of their mammograms)
The FDA approved the first "full-field" digital mammography scanner to screen for and diagnose breast cancer in February 2000. Before applying for FDA certification, data was gathered from 662 patients at four institutions: the University of Colorado, the University of Massachusetts Medical Center, Massachusetts General Hospital, and the Hospital of the University of Pennsylvania. The data compared hard copies of digital breast images on film to conventional mammography films finding that digital mammography is as effective at detecting breast cancer as standard film mammograms. A separate study revealed that the digital mammography scanner showed a slight advantage in the visibility of breast tissue at the skin line.
While digital mammography is quite promising, it still has additional hurdles to undergo before it replaces conventional mammography. Digital mammography must:
- provide higher detail resolution (as standard mammography does)
- become less expensive (digital mammography is currently several times more costly than conventional mammography)
- provide a method to efficiently compare digital mammogram images with existing mammography films on computer monitors
Standard mammography using film cassettes has the benefit of providing very high detail resolution (image sharpness), which is especially useful for imaging microcalcifications (tiny calcium deposits) and very small abnormalities that may indicate early breast cancer. While full-field digital mammography may lack the spatial resolution of film, clinical trials have shown digital mammography to be at least equivalent to standard film screening mammography. This is because digital mammography has the benefit of providing improved contrast resolution, which may make abnormalities easier to see. Various manufacturers are trying to develop digital mammography systems with detail resolution equivalent to standard film mammography while also providing the benefits of digital mammography noted above.
The high cost of digital mammography is a major obstacle. Digital mammography systems costs roughly 1.5 to 4 times as much as standard mammography equipment. Standard mammography systems are currently installed in over 10,000 locations across the United States. It may take years for this current equipment to be updated or replaced and for digital mammography to become widespread.
- The September 23, Imaginis report, "Study: Digital Mammography Better Than Standard Mammography at Detecting Breast Cancer in Some Women," is available at http://www.imaginis.com/breasthealth/news/news12.01.00.asp
- To learn more about the full-field digital mammography and other advances in breast imaging, please visit http://www.imaginis.com/breasthealth/news/news12.01.00.asp.
Updated: May 4, 2008
