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For other articles and previous issues click here. February 21, 2005 Mammography:
The Last Digital Frontier If large studies clarify clinical advantages and technology costs drop, then look for full-field digital mammography to be widely adopted. We’re not there yet. Full-field digital mammography (FFDM) is a relatively new x-ray technique that uses computers and specially designed detectors to quickly produce a digital image of the breast. Like film-screen mammography, it uses an x-ray beam to penetrate breast tissue, but the image is collected electronically and displayed on a computer monitor. Digital mammography is one example of new technology being utilized in the diagnosis of breast cancer that William R. Poller, MD, FACR, covered in his presentation at RSNA 2004. Poller, associate director of the breast care center of Allegheny General Hospital in Pittsburgh, spoke on implementing high-technology procedures in a breast center. As part of the presentation, Poller discussed the impact of FFDM, both from a diagnostic and financial standpoint—the two main issues for those considering digital mammography. Those issues raise important questions about the viability of digital mammography for many centers. Currently, data documenting the full extent of digital mammography’s benefits are rather nebulous. That may change when the results of a large-scale, multiyear, multicenter study are released sometime this year. In the meantime, the sketchy quantified benefits make it hard to justify the high price of digital mammography technology, especially for smaller facilities. Right now, implementation seems feasible only for a segment of the breast imaging community. FFDM Viability The first large multicenter study to compare digital mammography and standard mammography, the DMIST project involved nearly 50,000 women in the United States and Canada. Going into the study, the researchers suspected that the differences between digital and film mammography were not too great. Still, they believed it necessary to compare the two technologies. The study investigated diagnostic accuracy, sensitivity, specificity, positive and negative predictive value, and receiver operating characteristic performance. The subjects were women without symptoms or signs of breast cancer. They entered the study at the time of their regular screening mammogram and underwent both digital and film mammography. After one year, they repeated the two examinations. Each mammogram—both digital and conventional—involved two views of each breast. Two radiologists then viewed each woman’s images. One radiologist read the digital examination while the other read the film examination. “That study ended in November 2003, and data is currently being collected,” Poller said. “By November 2005, we should have some results. It’s going to show how digital and standard mammography really stack up against each other. So far, nothing has been conclusive.” Digital Advantages “I have been using digital for four years, so I will say that I think, in the dense breast, there is some advantage,” Poller said. “The feeling is that you can see through the breast tissue better if you can manipulate it online.” There are some other palpable advantages. “It gives you the ability to be filmless with no printing costs and to increase throughput,” said David Caumartin, sales and marketing manager of GE Healthcare in Waukesha, Wis. “Conceivably, on the average, you can put through three patients every 10 minutes or so with one technologist vs. one patient in every 10 minutes with two technologists for film.” But Poller indicated that there is a catch that comes with the throughput advantage. “For the radiologist, the time that is made up by the imaging—because it is quicker—is lost in the interpretation side because the radiologist still has to spend as much time and, in some cases, more time looking at the images because they are manipulating them,” he explained. Perhaps the most significant advantage of digital mammography is that it works well with computer-aided detection (CAD). “It’s easy to implement CAD with digital,” Poller said. CAD provides another “set of eyes.” Available software programs analyze and highlight areas that contain features that may be associated with cancer. Thus, these software programs may reduce the number of false-negative readings that result from observational lapses. Other benefits include the following: • Faster image acquisition. Conventional mammography exams take between 10 and 15 minutes while digital images are acquired in less than one minute. • Efficiency. Technologists know almost instantly whether images are of diagnostic quality. Technologists also seem to like the digital technology more, Poller noted. “From the radiologists’ standpoint, the value of digital mammography is still up in the air to some extent,” he said. “But from the technologists’ standpoint, it’s great. Digital mammography allows them to see the images right away, and there is less repeat.” • Reduced exam time. More women can be screened for breast cancer in a given amount of time. • Lower dose. Digital mammography also provides benefits for the patients. In general, the x-ray dose to the patient is somewhat lower. “There’s a lower dose rate but with the same image quality,” Caumartin said. • Filmless environment. The electronic data can be easily stored and retrieved, there are no problems associated with lost films, and film costs are greatly reduced. But there’s one more caveat: A totally filmless environment is not something that is going to be immediately realized. “Many places still have film screen because they haven’t been out long enough that they are only using digital images,” Poller said. “So they have to alternate digital with film screen. It’s a hassle, but it’s not insurmountable. The transition is just a little difficult. The radiology community knows that when they go digital, their lives will not suddenly become easier. That’s just not the case.” How It Works The displayed image can then be manipulated in numerous ways. It can be magnified, brightened, inverted, and sharpened, and the contrast can be changed. It is very similar to using a digital camera. After being displayed and manipulated, the image can be printed onto film. But until the results from the DMIST project are released, there really is no definitive way to answer the nagging question: As a diagnostic tool, is digital mammography truly more effective than standard mammography? Smaller and earlier studies, as well as some anecdotal evidence, don’t point to an overwhelming decision in favor of digital. While FFDM provides better contrast resolution, the spatial resolution is reportedly no better than—and may even be inferior to—conventional mammography. But this is something the DMIST researchers are trying to quantify. Cost: The Major Disadvantage Obviously, the larger facilities are best served by the technology. “They’re the ones who can most afford to invest in digital technology,” Poller said. “But it’s not so much that digital mammography has been completely proven yet. For the larger facilities, it’s the idea of being able to have a better mousetrap. They can say, ‘Come to our facility. We’re fully digital.’” However, as Poller indicated, the adjunct, or add-on, expenses inflate the price of digital mammography well beyond just the sticker price. Adjunct costs could make digital mammography financially unviable for even some of those larger facilities in larger, metropolitan markets. “The add-on costs are something everyone most definitely needs to consider,” Poller said. These include service contracts, storage capacity, and monitors. “The monitors cost about $40,000, and they last about two years,” he added. The service contracts for digital mammography cost more than a regular contract. The costs for one year of maintenance, together with equipment upgrades, can cost as much as a new film-based mammography unit. Image storage and retrieval can also be costly. “It depends on your volume,” Poller said. “You have to have storage capacity, depending on how much you want to spend on a jukebox [storage unit] and how much storage you want.” Reimbursement is another issue to consider. For the most part, FFDM is well-reimbursed by Medicare, as well as by many commercial payors. However, some commercial payors still consider FFDM investigational technology rather than a standard of care. That has led to reimbursement denials in some places. So, unless a facility does a high volume of mammography, the expenses associated with the digital technology can be prohibitive. If a facility does enough volume, conversion to digital may even be a smart financial move in the long run, but definitely not in the near term. “Someone has to be willing to make the investment and then take a loss for awhile,” said Poller. The more volume, the lower the cost per study. But for that to work out economically, a facility may need to do as many as 20,000 mammograms per year. Future Expansion Right now, cost is the prohibitive factor holding mammography back. “Because of the cost, it’s just not going to happen tomorrow,” he added. Factors that may help move mammography into the digital age include the results of the DMIST projects (if they’re favorable to digital) and the cost reductions that often accompany the continued development of a technology. With more manufacturers entering the market, costs of digital mammography equipment could drop significantly. If and when that happens, it could hasten widespread adoption of digital systems. — Dan Harvey is a freelance writer based in Wilmington, Del. He is a frequent contributor to Radiology Today. |
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