ABSTRACT
Nuclear medicine imaging systems, like positron emission tomography (PET) and single-photon-emission computed tomography (SPECT), rely on the use of scintillation detectors, which consist of inorganic scintillation crystals, and a photomultiplier tube (PMT). Visible light emitted by a scintillation crystal, due to its interaction with incident radiation, is converted into an electrical signal by a photocathode. This signal is then amplied by a strong electric eld between the cascading electrodes of a PMT, which is the most common type of photodetector used in the high-energy physics and medical imaging elds, and has been for more than 70 years (Figure 7.1a). However, PMTs are expensive, because many of their mechanical components are handmade. Furthermore, in the case of combined MRI and PET or SPECT units, PMTs must be intensively shielded from magnetic elds.
