Performance assessment of a novel readout circuit for time-of-flight positron emission tomography systems

Ziel/Aim For clinical positron emission tomography (PET) systems, precisely measuring the time-of-flight information in the order of few hundred picoseconds is key to improving the signal-to-noise-ratio in clinical imaging. A detector block commonly employed in PET systems to register the 511-keV gammas consists of a scintillation crystal coupled to a photosensor, which is read out by custom-designed electronics. In this study, we evaluate the impact of these three components on the time-of-flight performance of detector configurations that could be included into clinical systems.

Methodik/Methods A novel readout circuit, the TOFPET2 ASIC by PETsys Electronics S.A., is used to digitize the signal of the employed analog photosensors, here silicon photo-multiplier arrays fabricated by KETEK, SensL, Hamamatsu and Broadcom. Each sensor array is optically coupled to a pixelated lutetium-yttrium-oxyorthosilicate (LYSO) scintillator array of 12 mm height forming a PET detector block. We use the TOFPET2 ASIC Evaluation Kit which provides a small benchtop setup to connect different sensors to the readout electronics. Point-like positron-emitting Sodium-22 sources are used to evaluate the time-of-flight performance of different one-to-one coupled detector stacks.

Ergebnisse/Results The time-of-flight performance of the TOFPET2 ASIC in combination with silicon-photomultiplier arrays fabricated by different vendors was determined. Among the several configurations investigated, coincidence resolution times down to 219 ps were achieved with Hamamatsu arrays. In addition, energy resolutions in the order of 10 to 13 % were recorded allowing for the rejection of scattered events by an energy filter. The trigger logic implemented for the TOFPET2 ASIC can be configured to reject noise events.

Schlussfolgerungen/Conclusions As the digitization of 511-keV gammas by the TOFPET2 ASIC achieves coincidence resolution times in the order of state-of-the-art clinical PET systems, it can be considered as a promising alternative to be integrated into PET detector blocks.