The aim of the protoype built in the project is to perform the measurement of energy and time resolution achievable in a liquid xenon PET scanner. It consists of an aluminum box filled with LXe, with two arrays of SiPMs on opposite sides, which read out the scintillation light produced by a Na-22 calibration source placed in the middle. While some components of the prototype were purchased as commercial solutions, for instance, the cryocooler that liquefies xenon or the gas filter, most of them were designed specifically for this application. They include the gas system for the recirculation and purification of the gas, the vacuum vessel for thermal isolation, and the thermal links that connect the cryocooler with the xenon container and keep the temperature gradients under control. Especially crucial are the feedthroughs, which must bear high thermal stress and provide tightness to vacuum and liquid xenon pressure. A dedicated DAQ system was also developed, which reads the output of the ASICs that digitize the signal and distribute and synchronize signals from different ASICs. During the duration of the project, we tested the system, proving its excellent stability in the different phases of operation (filling, recirculation, data taking, recovery) and we characterised the full electronic chain and evaluated different kinds of SiPMs. After that, we measured the energy resolution using only scintillation light, achieving very good results for 511-keV gammas in liquid xenon. While this measurement needs to be refined, the first results already point to an excellent performance for liquid xenon, compared to the current state-of-the-art.
We have also measured the time resolution of liquid xenon, obtaining a result which is very competitive with the current commercial PET scanners. Excellent time and energy resolutions improve the quality of the images, allowing for achieving better images in less time.
At the same time, software tools for simulation, reconstruction and analysis were developed and Monte Carlo simulations were carried out, to guide the decisions on the design of the prototype and to study large-scale PET scanners to demonstrate the potential of the concept.
The performance of a full-body PET scanner was also studied, in particular we started to apply image reconstruction algorithms to the Monte Carlo simulation of a body-size PET. A first study was published, which assesses the attainable precision in the determination of the gamma interaction with a detector based in the PETALO concept. Moreover, we obtained a spatial resolution in the reconstructed image of around 1 mm for one point, a first proof the feasibility of the technology.
