Development of a SiPM-based PET imaging system for small animals Yanye Lu a , Kun Yang b,n , Kedi Zhou a , Qiushi Zhang a , Bo Pang a , Qiushi Ren a,nn a Department of Biomedicine and Engineering, College of Engineering, Peking University, Beijing 100871, China b Department of Control Technology and Instrumentation, College of Quality and Technical Supervision, Hebei University, Baoding, 071000, China article info Article history: Received 23 April 2013 Received in revised form 8 January 2014 Accepted 8 January 2014 Available online 18 January 2014 Keywords: Geiger-mode APD LYSO Instrumentation Animal imaging abstract Advances in small animal positron emission tomography (PET) imaging have been accelerated by many new technologies such as the successful incorporation of silicon photomultiplier (SiPM). In this paper, we have developed a compact, lightweight PET imaging system that is based on SiPM detectors for small animals imaging, which could be integrated into a multi-modality imaging system. This PET imaging system consists of a stationary detector gantry, a motor-controlled animal bed module, electronics modules, and power supply modules. The PET detector, which was designed as a multi-slice circular ring geometry of 27 discrete block detectors, is composed of a cerium doped lutetium–yttrium oxyorthosi- licate (LYSO) scintillation crystal and SiPM arrays. The system has a 60 mm transaxial field of view (FOV) and a 26 mm axial FOV. Performance tests (e.g. spatial resolution, energy resolution, and sensitivity) and phantom and animal imaging studies were performed to evaluate the imaging performance of the PET imaging system. The performance tests and animal imaging results demonstrate the feasibility of an animal PET system based on SiPM detectors and indicate that SiPM detectors can be promising photodetectors in animal PET instrumentation development. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Positron emission tomography (PET) is a nuclear medicine imaging technology that produces a three-dimensional functional image on the body. The PET imaging system detects two back-to- back 511 keV gamma photons produced simultaneously following positron–electron annihilation by a positron-emitting radionuclide (tracer). The tracer is introduced into the body via a radionuclide conjugated to a biologically active molecule. Advances in PET imaging have accelerated recently due to the development of a number of new technologies along with the use of small animal models in the basic and pre-clinical sciences [1–6]. Silicon photo- multiplier (SiPM, also called a multicell Geiger-mode avalanche photodiode) is a solid-state semiconductor photo sensor [7]. Each photon gives the same output signal where the strength is determined by the number of triggered APDs [8]. Compared with a photo multiplier tube (PMT), the SiPM detector has superior attributes such as high photon detection efficiency, compact size, insensitivity to magnetic fields, and low operating voltage; in addition, the quantum efficiency (  25%) and gain (  10 6 ) are similar to traditional PMTs [9–11]. The cerium-doped lutetium yttrium orthosilicate (Lu x Y 2 x SiO 5 :Ce, LYSO) scintillators are typical scintillators of choice for PET SiPM detectors. The LYSO scintillators exhibit several advantages including high light output and density, excellent energy resolution with quick decay time, no hygroscopic characteristics, and good stability. However, because Lu-based scintillators contain natural radioactivity from the decay of 176 Lu into 176 Hf, the background counts of LYSO scintillators are considerably higher compared with other scintillators [12]. In recent years, SiPMs have been successfully incorporated into some small animal PET scanners [13–18], and several small animal PET imaging prototypes [19–21] based on SiPM detectors have been developed. The results of these PET imaging prototypes have indicated that SiPMs have the necessary capabilities to be used in PET imaging devices. Our research group has been developing a multi-modality imaging system for preclinical studies. This system composes one anatomical imaging modality (i.e., X-ray computed tomography) and three major molecular imaging modalities [i.e., PET, single photon emission computed tomography (SPECT) and fluorescence molecular imaging (FMI)]. As an important part of the multi-modality imaging system, the PET system must be designed modularly and compactly, which means employing SiPMs is the best choice. The PET detector module is designed with a multi-slice circular ring geometry of discrete block detec- tors that are composed of LYSO and SiPM arrays. The electronic modules, which include the circuitry for pulse shaping, timing measurement, coincidence-detection, and communication dedi- cated to the PET imaging system were designed and fabricated. In addition, performance tests (e.g. spatial resolution, energy Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nima.2014.01.010 n Corresponding author. nn Corresponding author. Tel.: þ86 1062767113. E-mail addresses: yangkun9999@hotmail.com (K. Yang), renqsh@coe.pku.edu.cn (Q. Ren). Nuclear Instruments and Methods in Physics Research A 743 (2014) 30–38