[Development of Positron Emission Tomography Scanners Based on Positology].

This article gives a commentary on the development of positron emission tomography scanners based on Positology which was proposed by Dr. Eiichi Tanaka. Circular detector rings of an equally spaced detector arrangement have a problem of linear sampling density distributions in the projections. The problem can be solved by Positology in which a continuously rotating detector ring of an unequally spaced detector arrangement obtained by computer iterative searching provides a fine and uniform sampling density distribution. The imaging performance of multilayer positron emission tomography scanners for extended sources is evaluated analytically. The analysis is simplified by "rotation transform," by which three-dimensional photon detection problems are solved by two-dimensional treatment. Event rates of singles, unscattered true coincidence, and single- and double-scattered coincidence are formulated for a uniform cylindrical phantom. Positron emission tomography scanners based on Positology, named Positologica, were developed for brain, whole-body and animal study. A high resolution stationary PET scanner, SHR-1200 was also developed for brain study.