A modular hybrid PSPMT/SiPM depth encoding detector for high resolution positron emission tomography

PERFORMANCE of positron emission tomography (PET) scanners can be improved by using detectors that can measure depth of interaction (DOI) [1]. Dual ended readout is one of the widely studied methods to measure DOI. In this design two photodetectors are coupled to either end of a crystal or a block of crystals and DOI is estimated using the ratio of signal amplitudes recorded by the two photodetectors [2][3][4][5][6]. A hybrid dual ended readout DOI detector that uses a position sensitive photomultiplier tube (PSPMT) and an Avalanche photo diode (APD) for photodetection was presented in [2]. This prototype was further developed into a modular detector that encapsulates the electronic and mechanical functionality of a gamma detector to a compact self contained unit [7]. The modular detector can be easily integrated into new scanner designs with no changes to the detector itself. This facilitates rapid and cost effective development of application specific PET scanners. Such modules may also be rapidly transferred from one scanner gantry to another. The APD used in [7] requires a bias voltage of over 1800 V. The signal produced by APD is orders of magnitude smaller compared to PSPMT signal and requires extremely high amplification. Moreover, APD signal has to be routed near the body of the PSPMT. Therefore, shielding is required to reduce the interference from PSPMT. To address these shortcoming a modular detector was designed using SiPMs instead of APDs. SiPMs used in this detector requires bias voltages in the range 26V-29.5V and requires simpler amplifier circuitry due to the stronger signals produced.