Interest in these elements was lacking between the mid 1940s and early 1950s. Perhaps it was because of the discovery of Carbon-14 in 1940 by Kamen and Ruben. Carbon-14 proved to be a much more versatile and effective tracer than Carbon-11. Therefore this period of time for advancements in biomedical research along the lines of positron-emitting radionuclides seemed inconsequential. In the mid 1950s, Ter-Pogossian promoted the idea that in spite of the short half-lives of these positron-emitting radionuclides, they offered an attractive method for the regional study of metabolism due to their commonality.
Between the mid 1950s and the early 1970s, the utilization of these positron-emitting radionuclides was slow. It was not until a number of centers such as the Massachusetts General Hospital in Boston, the Sloan Kettering Institute in New York, Ohio State University, and the University of California at Berkeley, began to utilize cyclotrons that these positron-emitting radionuclides began to gain popularity. Three factors contributed to the development of this technology. First, was the fact that most metabolic processes in the body occur quickly enough to be traced by means of these short-lived positron-emitting radionuclides. Secondly, were the successes of a number of chemists in rapid labeling of complex molecules with the physiological labels in spite of their short life spans. Then, thirdly, was the realization that the penetrating radiation resulting from the annihilation of positrons made it obvious that the localization of these positrons was possible. [1]
Since the early 1970s, PET has been used as a research tool, and in more recent years has shown increasing potential for its application to clinical medicine. The first PET scanners used single slices when performing tomographs. These tomographs were produced in the early 1960s at several research institutes using systems with a ring of 32 NaI(Tl) detectors. The slice resolutions were greater than 2 cm full width half maximum (FWHM).
The following generation of PET scanners reduced detector size and added
additional rings to allow for simultaneous acquisition of multiple slices. The
slice resolutions improved from greater than 2 cm FWHM to less than 1 cm FWHM.
The majority of these complicated systems were one-of-a kind machines. In the
late 1970s marketing finally began making these machines the first commerically
available. As time progressed, more detectors and photomultiplier tubes (PMTs)
were added to these machines to increase their sensitivity and resolution. After
many years of study, a machine named the PENN-PET was developed at the
University of Pennsylvania. This machine consistedof a stationary array of six
positron detectors arranged in a hexagon around a 50 cm diameter patient port.
The PENN-PET offeredhigh sensitivity and a resolution of 5.5 mm FWHM and was
less complex and less expensive than systems with the ring detector designs. It
is commercially available. After years of advances made in PET research still
only a few more than a 100 centers exist worldwide. The majority of these
centers are dedicated to research, but a few are devoted to clinical use. [15]