Characterization of PETit: a TOF-PET prototype based on liquid xenon

Positron emission tomography (PET) is a medical imaging technique widely used in clinical diagnosis, especially in oncology, neurology, and cardiology. Its operation is based on the coincidence detection of the two 511 keV gamma photons produced after the annihilation of a positron emitted by a radiotracer with an electron from the surrounding medium. In order to obtain high-quality images, PET systems require detectors with excellent temporal, energy, and spatial performance. The final performance of the system strongly depends on the scintillation materials and photosensors employed. Liquid xenon presents very attractive properties for this type of application. Among its advantages is a high light yield, generating approximately 30,000 photons per 511 keV interaction, which enables good energy resolution. In addition, it possesses a fast scintillation component of only 2.2 ns, enabling excellent temporal performance and time-of-flight applications. Another important characteristic is that liquid xenon is transparent to its own scintillation light, allowing light collection. Furthermore, since it is in liquid form, it can be continuously purified through recirculation and filtration systems, achieving a homogeneous response throughout the detector. However, liquid xenon also presents limitations. The main one is its relatively low photodetection fraction, only 22%, as well as its attenuation length for 511 keV photons, which requires the use of thicker detectors to achieve efficiencies comparable to other materials. The PETit prototype was developed with the aim of studying the feasibility of liquid xenon as a detector medium for PET applications and characterizing its temporal and energy responses.

The work in this thesis has been carried out at the Instituto de Física Corpuscular (IFIC), affiliated with the Universitat de València and CSIC with the FPI grant PRE2021-097277