title: Simultaneous Multiparametric PET/MRI with Silicon Photomultiplier PET and Ultra-High-Field MRI for Small-Animal Imaging.
abstract: Visualization of biologic processes at molecular and cellular levels has revolutionized the understanding and treatment of human diseases. However, no single biomedical imaging modality provides complete information, resulting in the emergence of multimodal approaches. Combining state-of-the-art PET and MRI technologies without loss of system performance and overall image quality can provide opportunities for new scientific and clinical innovations. Here, we present a multiparametric PET/MR imager based on a small-animal dedicated, high-performance, silicon photomultiplier (SiPM) PET system and a 7-T MR scanner.
  
  
  METHODS
  A SiPM-based PET insert that has the peak sensitivity of 3.4% and center volumetric resolution of 1.92/0.53 mm(3) (filtered backprojection/ordered-subset expectation maximization) was developed. The SiPM PET insert was placed between the mouse body transceiver coil and gradient coil of a 7-T small-animal MRI scanner for simultaneous PET/MRI. Mutual interference between the MRI and SiPM PET systems was evaluated using various MR pulse sequences. A cylindric corn oil phantom was scanned to assess the effects of the SiPM PET on the MR image acquisition. To assess the influence of MRI on the PET imaging functions, several PET performance indicators including scintillation pulse shape, flood image quality, energy spectrum, counting rate, and phantom image quality were evaluated with and without the application of MR pulse sequences. Simultaneous mouse PET/MRI studies were also performed to demonstrate the potential and usefulness of the multiparametric PET/MRI in preclinical applications.
  
  
  RESULTS
  Excellent performance and stability of the PET system were demonstrated, and the PET/MRI combination did not result in significant image quality degradation of either modality. Finally, simultaneous PET/MRI studies in mice demonstrated the feasibility of the developed system for evaluating the biochemical and cellular changes in a brain tumor model and facilitating the development of new multimodal imaging probes.
  
  
  CONCLUSIONS
  We developed a multiparametric imager with high physical performance and good system stability and demonstrated its feasibility for small-animal experiments, suggesting its usefulness for investigating in vivo molecular interactions of metabolites, and cross-validation studies of both PET and MRI.
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea Department of Biomedical Sciences, Seoul National University, Seoul, Korea.
authors.forename: Guen Bae
authors.initials: GB
authors.lastname: Ko
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea Department of Biomedical Sciences, Seoul National University, Seoul, Korea.
authors.forename: Hyun Suk
authors.initials: HS
authors.lastname: Yoon
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea Department of Biomedical Sciences, Seoul National University, Seoul, Korea.
authors.forename: Kyeong Yun
authors.initials: KY
authors.lastname: Kim
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea Interdisciplinary Program in Radiation Applied Life Science, Seoul National University, Seoul, Korea.
authors.forename: Min Sun
authors.initials: MS
authors.lastname: Lee
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea Institute of Radiation Medicine, Medical Research Center, Seoul National University, Seoul, Korea.
authors.forename: Bo Yeun
authors.initials: BY
authors.lastname: Yang
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea Department of Biomedical Sciences, Seoul National University, Seoul, Korea Interdisciplinary Program in Radiation Applied Life Science, Seoul National University, Seoul, Korea Institute of Radiation Medicine, Medical Research Center, Seoul National University, Seoul, Korea.
authors.forename: Jae Min
authors.initials: JM
authors.lastname: Jeong
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea Interdisciplinary Program in Radiation Applied Life Science, Seoul National University, Seoul, Korea Institute of Radiation Medicine, Medical Research Center, Seoul National University, Seoul, Korea Department of Molecular Medicine and Biopharmaceutical Sciences, Graduate School of Convergence Science and Technology, Seoul National University, Suwon, Korea.
authors.forename: Dong Soo
authors.initials: DS
authors.lastname: Lee
authors.affiliation: Institute of Radiation Medicine, Medical Research Center, Seoul National University, Seoul, Korea Department of Radiology, Seoul National University, Seoul, Korea.
authors.forename: In Chan
authors.initials: IC
authors.lastname: Song
authors.affiliation: Department of Nuclear Medicine, National Cancer Center, Goyang, Korea; and Molecular Imaging and Therapy Branch, National Cancer Center, Goyang, Korea.
authors.forename: Seok-Ki
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Molecular Imaging and Therapy Branch, National Cancer Center, Goyang, Korea jaes@snu.ac.kr dkim@ncc.re.kr.
authors.forename: Daehong
authors.initials: D
authors.lastname: Kim
authors.affiliation: Department of Nuclear Medicine, Seoul National University, Seoul, Korea Department of Biomedical Sciences, Seoul National University, Seoul, Korea Interdisciplinary Program in Radiation Applied Life Science, Seoul National University, Seoul, Korea Institute of Radiation Medicine, Medical Research Center, Seoul National University, Seoul, Korea jaes@snu.ac.kr dkim@ncc.re.kr.
authors.forename: Jae Sung
authors.initials: JS
authors.lastname: Lee
mesh_terms: D000669:Amplifiers, Electronic / Q000662:veterinary; D000818:Animals; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000662:veterinary*; D051379:Mice; D008904:Miniaturization; D064847:Multimodal Imaging / Q000295:instrumentation* / Q000662:veterinary*; D010783:Photometry / Q000295:instrumentation / Q000662:veterinary; D049268:Positron-Emission Tomography / Q000295:instrumentation* / Q000662:veterinary*; D015203:Reproducibility of Results; D012666:Semiconductors; D012680:Sensitivity and Specificity; D014159:Transducers / Q000662:veterinary
keywords: PET/MRI; dual-modality imaging probe; hybrid imaging; multi-parametric imaging; silicon photomultiplier (SiPM)