The detector systems used almost exclusively in SPECT and PET systems are scintillation detector based. In these detector systems, the gamma rays emitted from the object that is being imaged will interact in the scintillation crystal. Depending on the interaction type, an energetic photoelectron or Compton electron is produced and set in motion, which will produce ionizations and excitations in the crystal. As the electrons de-excite back to the ground state, some of the transitions will result in the emission of light photons. The number of light photons emitted is proportional to the amount of energy that was transferred to the electron in the interaction. The purpose of a photodetector is to collect and absorb the scintillation photons and convert the light energy into an electrical signal that can be processed by the subsequent electronics to determine the energy and position of the interacting gamma ray.