IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 60, NO. 3, JUNE 2013 1533 MPPC Arrays in PET Detectors With LSO and BGO Scintillators T. SzczĊĞniak, Member, IEEE, M. Kapusta, Member, IEEE, M. Moszyński, Fellow, IEEE, M. Grodzicka, Member, IEEE, M. Szawłowski, Member, IEEE, D. Wolski, J. Baszak, and N. Zhang, Member, IEEE Abstract—Presently, a majority of studies concerning applica- tion of silicon photomultipliers (SiPMs) in positron emission to- mography detectors are focused on scintillators containing lan- thanum LaBr or lutetium (LSO, LYSO, or LFS). However, the modules with the well-known BGO in combination with SiPM light readout are also interesting, owing unique features of SiPMs. In this paper, the two types of detectors, based on BGO and LSO scin- tillators, are compared in terms of requirements for positron emis- sion tomography scanners. The presented studies are performed with two Hamamatsu Multi Pixel Photon Counter (MPPC) arrays of 2 2 channels, with the total area of mm and micro-pixel size of 25 m (S10985-025C) and 50 m (S10985-050C). The mea- surements of a number of photoelectrons, energy resolution at 511 keV and Na time resolution are reported for various sizes of the scintillators, including mm pixel and single crystals covering the whole MPPC active area. The paper is more focused on optimization of the system with BGO as its performance in combination with SiPM light readout is less known. The aim of this work is to show advantages of a SiPM-based detector, espe- cially in combination with BGO, in respect to the block detectors where classic photomultipliers are used. Index Terms—Energy resolution, number of photoelectrons, PET, silicon photomultipliers, time resolution. I. INTRODUCTION A silicon photomultiplier (SiPM), trademarked by Hama- matsu as a Multi Pixel Photon Counter (MPPC) became the candidate for a classic photomultiplier (PMT) successor in many applications. Positron emission tomography (PET) is one of the areas where detector modules with SiPM light readout are intensively studied. Presently, a majority of research studies concerning new SiPM-based PET detectors focus on modules with LaBr or with scintillators containing lutetium (LSO, LYSO or LFS-3 [1]), which are currently the most commonly used in commercial PET systems. Although BGO is the second most popular PET scintillator, its performance with SiPM light readout is much less known. Manuscript received February 07, 2012; revised December 17, 2012; accepted February 25, 2013. Date of publication April 05, 2013; date of current version June 12, 2013. This work was supported in part by the EU Structural Funds Project no POIG.01.01.02-14-012/08-00. T. SzczĊĞniak, M. Moszyński, M. Grodzicka, M. Szawłowski, and D. Wolski are with the National Centre for Nuclear Research (formerly the Soltan Insti- tute for Nuclear Studies), PL 05-400 Otwock-ĝwierk, Poland (e-mail: t.szczes- niak@ncbj.gov.pl). M. Kapusta and N. Zhang are with the Siemens Medical Solutions, Rockford, TN 37853 USA. J. Baszak is with the Hamamatsu Photonics Deutschland GmbH, D-82211 Herrsching am Ammersee, Germany. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TNS.2013.2251002 TABLE I MAIN PROPERTIES OF MPPCS USED DURING THE STUDIES Full body time-of-flight (TOF) PET could be built only by means of LSO detectors due to its high light output of 30 000 ph/MeV and fast decay time of 40 ns. However, in many PET studies where TOF information usefulness is limited by the size of the tested object or by the geometry of the system, like in PET mammography, PET prostate probes, brain studies in combination with MRI, or in small animal PET imaging, the BGO crystals read by SiPM array could be the perfect solution. The biggest advantage of this crystal is its 1.5 times higher, compared with LSO, detection efficiency of coincident 511 keV gamma rays. Moreover, BGO’s low-light output of 9000 ph/MeV and rather slow decay time of 300 ns became advantageous in combination with SiPM, extending its linear range. BGO also does not contain internal radioactivity, which is observed in the case of LSO due to naturally occurring (2.6%) Lu isotope. Finally, the price of BGO is considerably lower than LSO, which is especially important if the volume of scintillators is involved, as in the case of nuclear medicine devices. The aim of this work is to present and compare properties of detector modules based on BGO and LSO scintillators whose light is read by means of MPPC arrays. The studies are focused on measurements of photoelectrons’ number, energy resolution, and time resolution. The obtained results are benchmarked by PET requirements. II. EXPERIMENTAL DETAILS A. Photodetectors and Scintillators The studies were carried out with two Hamamatsu MPPC ar- rays of 2 2 active elements (channels) format. The total active area of each device is equal to mm , and the micro-pixel 0018-9499/$31.00 © 2013 IEEE