Positron emission tomography (PET) is an indispensable imaging technique in the field of nuclear medicine. Imaging is performed using $\beta ^+$ radionuclide, as the device detects collinear photons that are produced when a positron annihilates in matter.
The detector elements of PET devices are usually arranged in several rings. They consist of scintillation crystals that convert the annihilation photon into visible light and silicon photomultipliers that convert visible light into an electrical signal that is read by an electronic circuit.
The latest technological development of PET devices is in the direction of measuring the time of flight of photons, the development of larger devices for imaging the whole body simultaneously, and the development of devices with flat detectors. All of the mentioned advantages are combined in the PetVision project, under which a modular PET with flat detectors and time-of-flight measurement is being developed.
Unlike conventional ones, flat detectors do not cover a full angle, which can lead to distorted images. This is avoided by using time-of-flight measurements with a sufficiently good resolution, but good time resolution requires crystals that emit
light quickly. Their speed is characterized by two time constants - rise time and decay time.
The experimental part of the master’s thesis includes the setup of an experiment for time correlated single photon counting, which is used to measure scintillator time constants. The time constants of LYSO crystals from different manufacturers were
measured, followed by the measurement of time constants of crystals of different sizes, which explained the influence of crystal size on the measurement results.
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