ABSTRACT
The chapter about PET describes the physical principles and the advantages of this molecular imaging technique. Like SPECT, PET is also molecular imaging: the most important difference is, however, the different collimation method resulting in a much higher sensitivity for PET than for SPECT. At the basis is the use of positron emitters, which results in two opposed 511 keV photons at every decay. This allows for performing electronic collimation and leads to the principle of coincidence detection. To do this efficiently there are requirements on the scintillators for 511 keV coincidence imaging and the resulting detectors. There is constant evolution in PET systems aiming at increased sensitivity, better count rate, and improved spatial and energy resolution. An overview of the different generations of PET systems is given. The influence of the geometry and different ongoing improvements toward better performance are described (longer axial Field-Of-View, Time-Of-Flight). Finally, the physical limitations, corrections, and count-rate limitations of PET are discussed in detail.
