Development of ultra-fast ASIC for future PET scanners using TOF-capable MPPC detectors

We have developed a front-end ASIC (MPPC32) intended for future PET scanners that offers time-of-flight (TOF) capability in conjunction with a multi-pixel photon counter (MPPC) array. The ASIC design is based on the open-IP project proposed by JAXA and was realized in TSMC 0.35 - μ m CMOS technology. The circuit comprises 32-channel, low impedance CMOS current conveyors (CCs) to effectively acquire fast MPPC signals. In order to precisely measure the coincidence timing of 511 keV gamma rays, the leading-edge method was employed instead of conventional zero-crossing measurement to discriminate signals. As a result, we obtained time jitter and walk measurement of 67 ps (FWHM) and 98 ps (within 511 keV±20%), respectively. Moreover, excellent energy resolutions of 9.8% (662 keV; FWHM) and 10.5% (511 keV; FWHM) were obtained by utilizing a 3×3 mm2 MPPC (of 50 μ m pitch) coupled with a Ce-doped LYSO (Ce:LYSO) crystal 3×3×10 mm3 in size. We finally report on the TOF measurements, and demonstrate that the MPPC32 developed here can be a promising device for future TOF-PET scanners using the MPPC array.