Merging the functional imaging capabilities of positron emission tomography (PET) with the anatomic strengths of computed tomography (CT) into one combined modality has resulted in an imaging system that that is, by all accounts, greater than the sum of its parts.

GE Medical Systems (Waukesha, WI) installed the first such system, the Discovery LS, at the University Hospital, Zurich, Switzerland in March 2001. Siemens Medical Solutions (Erlangen, Germany) currently offers the biograph series, and Philips Medical Systems (Best, the Netherlands) recently introduced the GEMINI system.

Philips' GEMINI combines the ALLEGRO PET component with a high-throughput multislice CT scanner in the first open-format PET/CT system.

The Discovery LS from GE combines their Advance NXi PET technology with their LightSpeed multislice CT technology. Customers who currently have either individual modality are able to upgrade to the Discovery LS PET/CT.

Siemens' biograph combines a CT component from the SOMATOM Emotion spiral CT family with a choice of one of two PET scanner components: the ECAT HR+ or the ECAT ACCEL. Both systems work with the Windows-based syngo software platform. The major difference, according to the manufacturer, is that the ACCEL model employs the new LSO detector crystal, which allows for faster throughput. "The primary advantage of the HR+ is the slightly better resolution," said Vilim Simcic, PhD, vice president and general manager for PET at Siemens. "The advantage of the LSO is the very high throughput with ACCEL geared toward the high throughput oncology market."

According to Simcic, the standard biograph can image a typical patient from neck to pelvis in approximately 25 to 35 minutes. "With the biograph LSO, we have experience that actually went below 15 minutes," he reported. "What seems to be in the mindset is that PET examinations typically take an hour, and this is something that used to be true maybe 5 years ago. Since then, exam times have migrated down to 45 minutes, and with ACCEL, as a stand-alone system, they are on the order of 30 minutes. But with the addition of CT, we get more information and the throughput gets better as well. I think we are really changing the paradigm of how customers think about PET, especially with regard to throughput department."

Thomas Hook, general manager of Global PET at GE, noted that not only does the combined modality save time, it improves accuracy as well. "Before PET/CT hybrid imaging, it was necessary to order two exams, PET and CT," he said. "These separate exams, which could be conducted days, weeks, or even months apart, could introduce various image registration errors related to patient positioning and motion, making the diagnosis less accurate. With a PET/CT system, a single 30-minute exam is performed and the integrated PET/CT data achieves specificity that has been sought, but never realized, when images are produced from two separate systems."

Simcic also cites several other advantages of the combined modality. First, he said, "The combined modality provides more information; more precise anatomic location of the pathologic or benign uptake is seen in PET. PET is strictly functional and provides very limited anatomical information; adding CT to it gives very, very precise anatomical location of the pathological uptake. By complementing the two, I think it makes the overall sensitivity and specificity significantly better."

A second benefit is the reduced time needed to create an attenuation map. "This used to take a few minutes per patient and, in a few cases, depending on the PET scanner, maybe up to 10 minutes," Simcic noted. "Now CT data, which is acquired in minutes, is used to generate the attenuation correction. So in that sense, we are reducing the acquisition of the data for the attenuation correction from approximately 10 minutes to roughly 1 minute."

Hook notes that the combined image can improve the overall course of treatment for many patients as well. "The fusion of both functional and anatomic information from a single exam helps radiologists detect diseases earlier and diagnose them more precisely," he noted. "With a disease like cancer, for example, hybrid images can show clinicians the size and location of a tumor, which enables them to prescribe the most effective treatment path for the patient."

"According to our data, approximately 90% of Discovery LS studies are for a wide range of cancers, and approximately 5% are for neurologic disorders," said Hook. Simcic agrees, noting, "We generally used the combined PET/CT device for the approved clinical indications for which PET is used: basically, lung cancer, lymphoma, melanoma, head and neck cancer, and so on. In essence, most of the benefits are coming from the indications for PET. If we actually look at the utilization of the systems right now, it is driven by prevalence of the cancer and by reimbursement. For example, lung cancer is very prevalent and it is reimbursed and therefore it tops our list."

"What we are really hoping to do right now, with regard to PET in general," said Simcic, "is to get broader reimbursement for breast cancer. There is a limited reimbursement right now that is pretty fairly delineated. Obviously, the next step is broader reimbursement for cancers, which I think is a little further out in the future. There is a big potential on the neurology side with Alzheimer's disease."

"The PET reimbursement increases for breast oncology, myocardial viability studies, and, most recently, the pass-through reimbursement for FDG, all reflect a growing awareness and understanding of the clinical value of PET imaging," said Hook. "Because of the value provided by the CT component of PET/CT, we are optimistic that additional clinical indications will be approved for reimbursement in the future."

One future indication that Simcic is looking toward is radiation therapy planning. "Traditionally, the vast majority, or at least a lot of it, is being done using a CT system," he said. "Now, with the advent of PET/CT, one can actually get both modalities and modify the radiation plan based on which areas of the body are going to be irradiated based on more accurate information."

"One plus one truly is more than two in this case," concluded Simcic.

PET interactive distance learning program

In order to address some of the specialized learning requirements of nuclear medicine, GE recently launched a distance learning program focusing on the fundamentals of PET/CT hybrid imaging and PET oncology. The program, available to both physicians and technologists, is offered in both Internet and CD-ROM formats. The program uses interactive video, text, graphics, case studies, and testing to provide convenient, cost-effective education.

"The widespread adoption of PET and PET/CT systems has exposed more physicians, in many specialties of medicine, to PET imaging," said Hook. "This educational program, which was designed by physicians, for physicians, enables the user to learn about PET and PET/CT and be more skilled in the rapidly growing clinical applications of these technologies."

Course moderators include R. Edward Coleman, MD, Duke University Medical Center, Durham, NC; Homer Macapinlac, MD, MD Anderson Cancer Center, Houston, TX; Gustav von Schulthess, MD, PhD, University Hospital, Zurich, Switzerland; and Richard Wahl, MD, Johns Hopkins Medical Institutions, Baltimore, MD.

More information about this course can be obtained at the course website: http://apps.gemedicalsystems.com/geCommunity/nmpet/nm_education_index.jsp.

Perry named VP at AMS

American Medical Sales, Inc. (Hawthorne, CA) recently announced that J. Greg Perry has been promoted to vice-president, Sales and Marketing. In his new capacity, Perry is responsible for both domestic and international sales, as well as the company's marketing and technical divisions.

"This is a very exciting time to be in the industry," said Perry. "With the evolution of digital technology and PACS systems, there is tremendous opportunity for growth."

AMS offers a variety of imaging products including motorized viewers, film illuminators, and the digital viewing workstation, the Catella System.