Hybrid PET/CT scanners provided the excitement at the mid-June annual meeting of the Society of Nuclear Medicine. Vendors, led by GE Medical Systems—and its pre-SNM media blitz—hyped the clinical and economic importance of their newly
Hybrid PET/CT scanners provided the excitement at the mid-June annual meeting of the Society of Nuclear Medicine. Vendors, led by GE Medical Systems-and its pre-SNM media blitz-hyped the clinical and economic importance of their newly christened products.
GE described its Discovery family of CT/positron imagers as breakthrough technology. Initially shown as a work-in-progress at the 2000 RSNA meeting, the Discovery LS combines the company’s best dedicated PET scanner, Advance NXi, and its super premium CT, LightSpeed. At midtier is a repackaged work-in-progress version of SMV’s Positrace, outfitted with a HiSpeed CT scanner and new crystal and renamed Discovery VI. Filling out the family is Discovery VH, a dual-head gamma camera combined with CT technology.
Siemens Medical Solutions, which has been developing tools to fuse CT and nuclear medicine images for the better part of a decade and has the longest clinical experience with hybrid PET/CT scanning, showcased its Biograph PET/CT scanner, originally unveiled at the 2000 RSNA meeting. Philips ADAC directed attention to its work-in-progress Gemini PET/CT scanner. Both companies have less costly gamma cameras outfitted for positron imaging: Siemens’ E.CAM Duet and ADAC’s Forte.
The flagship products-Discovery LS, Biograph, and Gemini-represent the largest single diagnostic investment radiology can make. These hybrids are literally two devices rolled into one and, when million-dollar multislice scanners join $1.5 million dedicated PET systems, list prices swell to more than $2 million. Despite the astronomical price tags, vendors predict gangbuster sales. Vendors already have a substantial investment in PET/CT scanners. GE, for example, has invested $50 million in development of Discovery LS, which lists for $2.7 million.
At a New York City press conference in the days before the meeting and again on the SNM exhibit floor, GE’s vice president and general manager of global functional and molecular imaging, Beth Klein, predicted customers would buy 500 Discovery products over the next three years. On the SNM exhibit floor, Siemens’ strategic marketing manager, Elbert Lands, asserted that Siemens would keep pace with GE. But neither company would predict how many sales would be CT/gamma cameras or dedicated PET/CTs.
Lost in the promotional flurry was the fact that fewer than a dozen PET/CT systems have actually entered clinical service, and early experience indicates their use might be justified only under very specific circumstances.
“Hybrid systems fit in a number of areas but not in all of therapeutic monitoring for cancer and not in all of cancer staging,” said Dr. Carolyn C. Metzler, medical director of the University of Pittsburgh PET facility. “They really fit where our conventional imaging has trouble-certain anatomic areas and certain tumors that are notoriously difficult to image.”
For some patients, however, PET/CT could have substantial impact. Preliminary studies done at several sites around the world and presented in scientific sessions at the SNM documented operable cancers that might otherwise have been termed inoperable and excluded disease in patients whose FDG uptake was not related to cancer. Hybrid imaging could prove especially useful in the future, when the expected wave of new cancer drugs arrives and oncologists seek to tailor therapy to maximize patient response, presenters said.
Reporting on studies of some 300 patients scanned with Siemens’ Biograph, Metzler highlighted cancers of the head and neck as among those best suited to evaluation with the hybrid technology, especially when patients have had repeated surgery and radiotherapy. Pancreatic assessment is difficult with CT alone but improves with hybrid imaging, she said. The same is true for small lesions near the bladder, which might be missed on PET but can be distinguished with CT-provided landmarks. PET/CT also promises the functional and anatomic accuracy needed to track the response to therapy of lymphoma, whose tumors may shrink with treatment but not go away.
The road to these benefits will not be a smooth one, however, at least not in the early going. Still to be worked out is how to physically position the patient. Using GE’s Discovery LS to study 16 patients, physicians at Rambam Medical Center in Haifa, Israel, concluded that PET/CT improved diagnostic accuracy and tumor localization, but interpretation may be complicated by artifacts resulting from inadequate patient positioning. Dr. Ora Israel, director of the department of nuclear medicine, and her colleagues at Rambam, initially placed patients’ arms above their heads, as is typically done for CT scans to avoid beam hardening artifacts. Ideally, patients should stay in exactly the same position for the PET exam, but elderly patients participating in the study could not hold that position for the half-hour PET exam. The physicians had to choose between potential misregistration and beam hardening artifacts.
“The engineers will have to deal with that problem,” Israel said. “We are just physicians.”
Customers without deep pockets might buy a gamma camera-based PET system for under a million dollars. These scanners offer less resolution than the flagship products but still improve clinical assessments. A more economical solution for current owners of CT and PET scanners is software that fuses data sets from the two modalities.
At the SNM meeting, Dr. Suzanne L. Aquino, an assistant professor of radiology at Harvard University, documented that the fusion of separately acquired CT and PET images improves localization of metastatic disease. In four of 16 patients, apparently abnormal FDG uptake was excluded, and two other cases of FDG uptake were ascribed to radiation changes. Another that would have been missed on CT alone was found to be a residual tumor. All conclusions were later proven on follow-up.
“Hybrid scanners are very expensive,” Aquino said. “Not everybody is going to be able to afford them. By registering data sets using diagnostic studies, we can still improve our staging and diagnosis of cancer.”