title: Development of small-animal PET prototype using silicon photomultiplier (SiPM): initial results of phantom and animal imaging studies.
abstract: Silicon photomultiplier (SiPM; also called a Geiger-mode avalanche photodiode) is a promising semiconductor photosensor in PET and PET/MRI because it is intrinsically MRI-compatible and has internal gain and timing properties comparable to those of a photomultiplier tube. In this study, we have developed a small-animal PET system using SiPMs and lutetium gadolinium oxyorthosilicate (LGSO) crystals and performed physical evaluation and animal imaging studies to show the feasibility of this system.
  
  
  METHODS
  The SiPM PET system consists of 8 detectors, each of which comprises 2 × 6 SiPMs and 4 × 13 LGSO crystals. Each crystal has dimensions of 1.5 × 1.5 × 7 mm. The crystal face-to-face diameter and axial field of view are 6.0 cm and 6.5 mm, respectively. Bias voltage is applied to each SiPM using a finely controlled voltage supply because the gain of the SiPM strongly depends on the supply voltage. The physical characteristics were studied by measuring energy resolution, sensitivity, and spatial resolution. Various mouse and rat images were obtained to study the feasibility of the SiPM PET system in in vivo animal studies. Reconstructed PET images using a maximum-likelihood expectation maximization algorithm were coregistered with animal CT images.
  
  
  RESULTS
  All individual LGSO crystals within the detectors were clearly distinguishable in flood images obtained by irradiating the detector using a (22)Na point source. The energy resolution for individual crystals was 25.8% ± 2.6% on average for 511-keV photopeaks. The spatial resolution measured with the (22)Na point source in a warm background was 1.0 mm (2 mm off-center) and 1.4 mm (16 mm off-center) when the maximum-likelihood expectation maximization algorithm was applied. A myocardial (18)F-FDG study in mice and a skeletal (18)F study in rats demonstrated the fine spatial resolution of the scanner. The feasibility of the SiPM PET system was also confirmed in the tumor images of mice using (18)F-FDG and (68)Ga-RGD and in the brain images of rats using (18)F-FDG.
  
  
  CONCLUSIONS
  These results indicate that it is possible to develop a PET system using a promising semiconductor photosensor, which yielded reasonable PET performance in phantom and animal studies.
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea.
authors.forename: Sun Il
authors.initials: SI
authors.lastname: Kwon
authors.forename: Jae Sung
authors.initials: JS
authors.lastname: Lee
authors.forename: Hyun Suk
authors.initials: HS
authors.lastname: Yoon
authors.forename: Mikiko
authors.initials: M
authors.lastname: Ito
authors.forename: Guen Bae
authors.initials: GB
authors.lastname: Ko
authors.forename: Jae Yeon
authors.initials: JY
authors.lastname: Choi
authors.forename: Sung-Hyuk
authors.initials: SH
authors.lastname: Lee
authors.forename: In
authors.initials: I
authors.lastname: Chan Song
authors.forename: Jae Min
authors.initials: JM
authors.lastname: Jeong
authors.forename: Dong Soo
authors.initials: DS
authors.lastname: Lee
authors.forename: Seong Jong
authors.initials: SJ
authors.lastname: Hong
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000000981:diagnostic imaging; D001921:Brain / Q000000981:diagnostic imaging; D004581:Electronics; D004867:Equipment Design; D019788:Fluorodeoxyglucose F18; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009942:Organometallic Compounds; D004369:Pentetic Acid / Q000031:analogs & derivatives; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation*; D019275:Radiopharmaceuticals; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; C531177:gadolinium-DTPA-g-mimRGD; D019788:Fluorodeoxyglucose F18; D004369:Pentetic Acid