BBI Contributing Editor

Part 1 of 2

CHICAGO, Illinois The 88th annual meeting of the Radiological Society of North America (Oak Brook, Illinois), held in early December in the sprawling McCormick Place along Chicago's snow-covered Lake Michigan shoreline, saw attendance bounce back from last year's post-9/11 tumble. Just under 60,000 radiologists, technicians, exhibitors and others attended, up 11% from last year and putting the meeting back on its traditional growth track after a tumble in attendance in 2001. About 1,700 scientific papers and 500 scientific posters were presented, and more than 600 suppliers exhibited their wares.

As usual, the perennial question asked by nearly all attendees was, "What have you seen that's new and interesting?" The answer has to be, "Not much that's really new, but quite a lot that's interesting." In 1972, the RSNA meeting was electrified by demonstrations of computed tomography (CT). A decade later, magnetic resonance (MR) made its debut. The next year, Acuson (Mountain View, California), now part of Siemens, revolutionized the seemingly mature field of ultrasound with a device that doubled spatial resolution and doubled the price for equipment. About the same time, Fuji (Stamford, Connecticut) introduced what came to be known as computed radiography (CR), the forerunner in the gradual, ongoing conversion of X-ray procedures to the digital realm. Nuclear medicine was reaping the benefits of single-photon emission CT (SPECT), which greatly increased its utility in cardiac imaging. Nothing of comparable potential exists in medical imaging today.

But this is not to say that nothing of interest exists. On the contrary, many developments are bearing fruit, and the outlines of two gradually developing trends were the focus of plenary sessions at this year's meeting. One was RSNA President Nick Bryan's presentation of "The Digital rEvolution in Radiology." The peculiar spelling was deliberate, intended to emphasize the fact that conversion to digital is evolutionary proceeding gradually while its culmination will be revolutionary. Procedures using the digital modalities (everything except film radiography, which still accounts for about half of all imaging procedures) continue to grow in number and as a proportion of all imaging procedures. At the same time, the number and proportion of X-ray procedures using digital devices (computed radiography and digital radiography) also grows, so that there is no doubt that ultimately all procedures will be digital.

The implications of this evolution are profound. Picture archiving and communication systems (PACS, as these medical image management systems are known) furnish an important and growing market that now in the U. S. amounts to about $1.2 billion, comparable to the markets for CT ($1.3 billion) or ultrasound ($1.1 billion), though surpassed by the markets for X-ray ($1.8 billion) or MR ($1.9 billion). However, the PACS market is growing faster than any other part of the market. Going digital modifies the way that radiology is practiced, making possible much faster turnaround of results, ready access to archived images for comparison, remote reading of images, easy transfer of images to referring physicians, full integration with hospital information systems, application of computer-aided diagnosis, generation of 3-D and 4-D (3-D images that change with time) presentations, 24/7 coverage, and easy application of quantitative methods.

All of these developments are in full-blown expansion today. Looking to the more distant future, another set of trends was addressed in the New Horizons Lecture, given this year by Bruce Rosen, MD, PhD, director of the Center for Biomedical Imaging at Massachusetts General Hospital (Boston, Massachusetts), in a talk titled, "Functional Imaging of the Brain in Space and Time." Traditional medical imaging as currently practiced by most radiologists is based on delineating the shape of macroscopic internal structures. Abnormalities such as tumors, aneurysms, malformations, broken bones, and bleeding are recognized by their characteristic shapes in an image. Even nuclear medicine, whose main strength lies in its ability to measure function by observing the fate of injected or ingested radiopharmaceuticals, relies on changes in the shape of images made at certain stages in time. Methods both old and new can be used to measure function, not only of whole organs, like the heart, lungs or kidneys, but also of small collections of cells. Such techniques have important implications for diagnostic practice, therapeutic interventions, and medical and scientific research.

Rosen and his colleagues have developed methods using MR to localize sites of increased cerebral activity, using the fact that such sites have increased blood flow and increased production of deoxyhemoglobin, which acts as a natural MR contrast agent. The ability to recognize such sites, combined with the anatomical precision now available from MR, has many applications. He observed that functional MR is now routine in some institutions in preparing patients for brain surgery, where the surgeon must plan an approach to a lesion that spares regions of the brain that control motor activity, seeing, hearing and speech. Such studies are useful in understanding and evaluation of neurodegenerative diseases, stroke and epilepsy, as well as evaluating therapies addressed to these ailments. They may be even more valuable in understanding human diseases for which no suitable animal models exist, such as schizophrenia, depression, autism and substance abuse, possibly linking radiology and psychiatry much more closely than ever before.

One consequence of these developments will be increased use of 3-tesla magnets, which enhance the signals necessary for functional MR over those available from conventional 1.5-tesla and smaller magnets. Presently, the FDA regards fields higher than 2 tesla as investigational, but this restriction will almost surely be relaxed since no evidence of harm from higher fields has emerged. Three-tesla machines are available for research purposes from GE Medical Systems (Waukesha, Wisconsin), Siemens (Erlangen, Germany) and Philips Medical Systems (Bothell, Washington).

Magnetic resonance is not the only technique for functional imaging. Nuclear medicine, especially positron emission tomography (PET), also provides functional information. PET has been commercially available for 30 years, but its utilization was severely impeded by its cost and inconvenience. The machines are expensive ($1.5 million to $2 million), and a center needed a cyclotron to generate the short-lived radioisotopes that are used in PET imaging, while most insurers would not pay extra for PET procedures. In the past couple of years, three things have changed to make PET a booming market. One was Medicare approval of PET for reimbursement of $1,200 to $1,500 per procedure. Another was the growth of nuclear pharmacies that distribute fluorodeoxyglucose (FDG), the principal imaging agent used in PET. Now the three leading imaging companies that produce 3 Tesla MR also produce combined PET/CT systems, which allow fusion of CT and PET images.

Where PET had not been economically viable, reimbursement erased that problem. Where generation of short-lived radioisotopes such as carbon, oxygen, nitrogen and fluorine had been expensive and time-consuming, nuclear pharmacies serving a local area solved that problem. Where PET's rather murky images were hard to relate to specific anatomical structures, combined PET and CT solved that problem. The result has been a boom in PET sales, giving a boost to the field of nuclear medicine.

Rosen also drew attention to imaging with light, a field with a checkered past. In the 1980s, a few companies championed diaphanography, in which light was shone through a breast to detect internal tumors. The method worked, but it succeeded only when the tumor was large and near the surface, and the method was hardly better than palpation. Despite a great deal of marketing hype, the radiology profession rejected the technique as inefficacious. But newer techniques hold greater promise. Britton Chance, a professor emeritus at the University of Pennsylvania (Philadelphia, Pennsylvania), has shown that tumors absorb infrared light of a certain wavelength more than does normal tissue because tumors are sites of active metabolism and angiogenesis, generating more deoxyhemoglobin. Such sites can be localized by illuminating tissue with infrared light and using methods analogous to the methods of CT to create an image. The initial clinical promise of this technique may be in detecting breast tumors or problems of regional perfusion in the brains of neonates. It may also be valuable in detecting early response to therapeutic interventions like chemotherapy or radiation.

Yet another new direction highlighted at this year's meeting was molecular biology. C. Norman Coleman of the National Cancer Institute (Bethesda, Maryland) gave the annual oration in radiation oncology titled, "Linking Radiation Oncology and Imaging through Molecular Biology." Thanks to the breathtaking new techniques for analyzing DNA, proteins and the molecular components of cells, our understanding of normal and pathological functions at the molecular and cellular levels is growing rapidly. Established treatments such as chemotherapy and radiation have been purely empirical, trying various compounds and radiation techniques to find ones that worked. Now, a theoretical, measurable framework for these techniques is emerging and with it a new discipline, molecular biology. It means that it will be possible to use radiation or cytotoxic chemicals in a way that is precisely targeted to the cells in question and readily measured to ascertain the effects of interventions. Through their images, radiologists have had a role in treatment planning, staging, and assessment of treatments. Through these new techniques, radiologists may still have a role if they grasp these opportunities.

Another subject of interest at this year's gathering was the shortage of trained radiologists. It is acute. As now is well known, imaging plays a central role in diagnosis, and the fact is driven home by the rise in imaging procedures, which have been increasing in number by more than 10% per year for the past several years with no end in sight. As a result, there is a need for more radiologists. The number of radiologists currently being trained is far short of the number needed. The only near-term solution lies in having radiologists work more efficiently, and to a certain extent this is happening, thanks to PACS. From the standpoint of radiologists now in practice, this development is a happy one, assuring them a comfortable future. RSNA 2002 reinforced this view.

(Next month: Commercial developments revealed at RSNA 2002.)