Digital mammography is inevitable. People may argue over the details, but everyone accepts the fact that screen-film mammography-radiology's last major analog holdout-cannot stand forever.
Radiology's response so far to digital mammography, however, has been surprisingly tepid. In the four years since the first full-field unit hit the market, fewer than 10% of the 9000 government-accredited mammography facilities in the U.S. have gone digital. The circumspection shown by prospective buyers, which until recently was chalked up to high capital costs, remains pervasive.
Given the rock-bottom reimbursement rates for mammograms, this measured response to the purchase of expensive equipment is entirely rational. Early adopters are willing to pay a premium to become fully digital, accepting operational losses at a somewhat greater rate. They have gained workflow and organizational efficiencies that can begin to justify their investment, and most say they are happy to be over the digital divide, despite the cost. Yet doubts about the technology complicate the conversion process.
One factor that has chilled the market is the American College of Radiology Imaging Network study, which was launched in 2001. Published results from the ACRIN trial are expected early next year. Should investigators report digital mammography to be as good as or better than conventional mammography at detecting breast cancer, which the study was designed to evaluate, many groups will jump off the fence and quickly convert to digital. Conventional wisdom predicts, however, that the trial will not show strong power in favor of digital mammography, leaving its clinical utility as debatable as ever.
Many pundits, in fact, believe digital mammography to be superior in breast cancer diagnosis, and they have been showing cases at conferences for months that back up their contention. Digital mammograms are not destined to be conducted in isolation, however, nor read at leisure. They are reviewed on busy workstations, and that is the rub for community radiologists. Just as important as reimbursement and what the experts think of digital mammography are the speed and ease with which screening studies can be read. Complicating or slowing down any reading protocol creates a big problem. The speed with which screen-film studies can be read sets a demanding standard.
The same academic leaders who can show outstanding examples of subtle breast cancer on digital mammograms have yet to agree on how best to display the images or on the best integrated enhancements to digital mammography. The choir is not yet singing in unison.
Digital mammograms cannot be cheaply integrated into a PACS because of the need for high-resolution monitors. They have to be displayed on a dedicated workstation. At many sites, use of a single workstation would create a crunch in throughput as readers fight over access. Somebody trying to read screening exams from the day before is not compatible with someone else needing to do a diagnostic workup stat. Furthermore, workstations to date are propriety in design, and some cannot display images from other vendors. Third-party workstations that can display and manage digital exams from all comers are badly needed, and these are reportedly in the pipeline.
Most of the operational efficiencies of digital mammography currently accrue to technologists. This is good in that acquisition technology has become highly refined, but vendors should focus now on what happens to those images at the back end where the radiologists are. Workflow protocols involving the calling up of priors, possibly from more than one vendor's system, along with current mammograms in an intuitive display that can match the quality of a board of film remain elusive. Serious teachers of mammography cannot say at this stage that digital mammography is an improvement in breast cancer screening.
CHALLENGE FROM OTHER MODALITIES
The fact that projection radiography is no longer the default modality for all breast disease imaging creates another set of challenges for digital mammography. Since digital mammography emerged in the early '90s, ultrasound has become more important for imaging dense breasts and certain common abnormalities, and breast MR imaging has become the hottest kid on the block. Patients at high risk for breast cancer could be diverted from mammography to MRI, or at least receive supplemental MRI, following the positive findings of a study from the Dutch Health Insurance Council published last July in the New England Journal of Medicine.
What hasn't been lost on those watching their cash flow is that while an MR study can cost 10 times that of a conventional mammogram, many large insurers cover MRIs for women at high risk for cancer. For the cost of a mammo coil and a weekend training course, a radiology group can move into breast MRI and improve its bottom line in breast imaging. Given this option, some practices will opt for a multimodality approach to breast diagnosis that distracts them from digital mammography.
The use of ultrasound and MRI in the breast will also dramatize the limitations of current workstations. Radiology has already entered into multiplanar space with multidetector CT and is dabbling with 3D across the modalities. The push to work with 3D data sets is intensifying. When mammographers sit down to read cases in the future, they will want to see digital x-rays, but they will also want the capacity to quickly and easily call up ultrasounds and MRIs. The workstations they use will need to be breast imaging-specific, and not just mammography-specific.
Two new applications in digital mammography that should help minimize the effects of tissue superimposition, and thus respond to the siren call of multiplanar imaging, are tomosynthesis and contrast subtraction mammography. Tomosynthesis produces quasi-3D images of x-ray attenuation within the breast, in many cases making lesions easier to identify. Contrast subtraction mammography, while objectionable on the basis of its invasiveness, may facilitate detection of breast cancer in women for whom the effects of angiogenesis can be measured.
Tomosynthesis requires design changes to the mammography machine itself, since the breast must be viewed from different angles. Images made at Massachusetts General Hospital and elsewhere look promising, but the practical logistics of tomosynthesis, to say nothing of its cost, are not yet fully understood.
Ultimately, everything that mammographers say they want in a workstation is possible. Advances in PACS show how demand has shaped software innovations. It may take time-even years-before economic incentives are sufficient to deliver a breast imaging workstation that matches a standard PACS, however. Until the incentives emerge, we can expect digital mammography to remain a market underachiever.
Mr. Ogle is a freelance healthcare writer and media consultant. He can be reached at 541/754-5458 or firstname.lastname@example.org.
Mr. Ogle does contract editing and writing for Fuji Medical Systems.
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