Design changes and availability spark PET/CT revolution

Ongoing technological improvements and sustained growth in the number of scanners worldwide are helping to fuel the rapid growth in clinical PET/CT.

About 200 combined systems have been installed worldwide since the first PET/CT scanner was introduced in June 2000, Prof. Dr. Thomas Beyer from the nuclear medicine department at the University Hospital Essen in Germany told a refresher course on Sunday.

Among the important technological trends are the introduction of high-performance PET technology, revised detector electronics (pico3D), high-resolution detectors (HiRez LSO), revised BGO gantries, respiratory and cardiac gating, and 64-slice CT scanners.

LSO crystals are replacing BGO crystals, and GSO is replacing NaI. The type of crystals used in PET/CT has an impact on the speed and resolution of scanners.

Beyer listed the following design goals of PET/CT: no bed deflection, whole-body coscan range, high-performance CT, subsecond rotation, highest PET performance, increased CT field-of-vision, increased port diameter, and integrated acquisition.

"Current hardware and software developments focus on increasing the throughput of PET/CT and offering alternative clinical acquisition protocols," he said. "Revised PET detector designs and a more integrated high-end combination of CT and PET technology may lead to a more novel research tool for combined imaging of highly specific tracers."

Beyer finished his talk by repeating a statement made at the 2003 meeting of the German Society of Nuclear Medicine by Dr. Johannes Czernin, director of nuclear medicine in the medical and molecular pharmacology department at the University of California, Los Angeles: "In technical terms PET/CT is an evolution. In medical terms PET/CT is a revolution."

The number of dedicated PET scanners installed worldwide between 1992 and 2002 was 1600 - 1020 in the U.S., 470 in Europe, and 110 in Japan - according to Prof. Dr. Richard P. Baum from the department of nuclear medicine and Center for P.E.T., Zentralklinik Bad Berka in Germany.

About 100 of these scanners are located in Germany, compared with 84 in Italy, 63 in France, 43 in Spain, 22 in the Netherlands, 17 in Belgium, 15 in Greece, and eight each in Austria and Denmark.

The number of planned installations for Europe over the next five years is 116. A total of 30 scanners are due to be installed in Italy, 24 in France, 21 in Spain, 8 in the U.K., six in Sweden, five in Finland, and four in Belgium. The number of cyclotrons in Europe in 2001 was 62. A further 22 were planned for the next five years.

The indications for PET in melanoma are primary staging of high-risk melanoma (Clark Level III or higher) and restaging in patients with suspected or proven recurrence before surgical intervention. In suspected cases of lymphoma, the indications of PET are primary staging (nodular/extranodular involvement) of high-grade lymphoma and restaging after chemotherapy or radiation therapy (differential diagnosis between residual tumour and fibrosis), he said.

In the brain, PET's great strength is its ability to distinguish between recurrent tumor and radiation necrosis. The modality can also produce a differential diagnosis (tumor versus nontumor) and provide details about the histological grade of the malignancy, survival time, tumor extent in the case of low-grade tumors. Additionally, it can localize areas of high cell density and can be used to monitor therapy.

"In the future, immuno-PET and receptor-PET will improve dosimetry of radionuclide therapy and by using reporter genes, gene-PET will enable monitoring of gene therapy," Baum said.