High-performance electronics for time-of-flight PET systems

Abstract

We have designed and built a high-performance readoutelectronics system for time-of-flight positron emission tomography (TOF PET)cameras. The electronics architecture is based on the electronics for acommercial whole-body PET camera (Siemens/CPS Cardinal electronics),modified to improve the timing performance. The fundamental contributions inthe electronics that can limit the timing resolution include the constantfraction discriminator (CFD), which converts the analog electrical signalfrom the photo-detector to a digital signal whose leading edge istime-correlated with the input signal, and the time-to-digital converter(TDC), which provides a time stamp for the CFD output. Coincident events areidentified by digitally comparing the values of the time stamps. In theCardinal electronics, the front-end processing electronics are performed byan Analog subsection board, which has two application-specific integratedcircuits (ASICs), each servicing a PET block detector module. The ASIC has abuilt-in CFD and TDC. We found that a significant degradation in the timingresolution comes from the ASIC's CFD and TDC. Therefore, we have designedand built an improved Analog subsection board that replaces the ASIC's CFDand TDC with a high-performance CFD (made with discrete components) and TDC(using the CERN high-performance TDC ASIC). The improved Analog subsectionboard is used in a custom single-ring LSO-based TOF PET camera. Theelectronics system achieves a timing resolution of 60 ps FWHM. Prototype TOFdetector modules are read out with the electronics system and givecoincidence timing resolutions of 259 ps FWHM and 156 ps FWHM for detectormodules coupled to LSO and LaBr3 crystals respectively.