title: Development of a flexible optical fiber based high resolution integrated PET∕MRI system.
abstract: OBJECTIVE
  The simultaneous measurement of PET and magnetic resonance imaging (MRI) is an emerging field for molecular imaging research. Although optical fiber based PET∕MRI systems have advantages on less interference between PET and MRI, there is a drawback in reducing the scintillation light due to the fiber. To reduce the problem, the authors newly developed flexible optical fiber bundle based block detectors and employed them for a high resolution integrated PET∕MRI system.
  
  
  METHODS
  The flexible optical fiber bundle used 0.5 mm diameter, 80 cm long double clad fibers which have dual 12 mm × 24 mm rectangular inputs and a single 24 mm × 24 mm rectangular output. In the input surface, LGSO scintillators of 0.025 mol.% (decay time: ∼31 ns: 0.9 mm × 1.3 mm × 5 mm) and 0.75 mol.% (decay time: ∼46 ns: 0.9 mm × 1.3 mm × 6 mm) were optically coupled in depth direction to form depth-of-interaction detector, arranged in 11 × 13 matrix and optically coupled to the fiber bundle. The two inputs of the bundle are bent for 90°, bound to one, and are optically coupled to a Hamamatsu 1-in. square position sensitive photomultiplier tube.
  
  
  RESULTS
  Light loss due to the fiber bundle could be reduced and the performance of the block detectors was improved. Eight optical fiber based block detectors (16 LGSO blocks) were arranged in a 56 mm diameter ring to form a PET system. Spatial resolution and sensitivity were 1.2 mm full-width at half-maximum and 1.2% at the central field-of-view, respectively. Sensitivity change was less than 1% for 2 °C temperature changes. This PET system was integrated with a 0.3 T permanent magnet MRI system which has 17 cm diameter hole at the yoke area for insertion of the PET detector ring. There was no observable interference between PET and MRI. Simultaneous imaging of PET and MRI was successfully performed for small animal studies.
  
  
  CONCLUSIONS
  The authors confirmed that the developed high resolution PET∕MRI system is promising for molecular imaging research.
authors.affiliation: Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan. s-yama@met.nagoya-u.ac.jp
authors.forename: Seiichi
authors.initials: S
authors.lastname: Yamamoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Watabe
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Kanai
authors.forename: Tadashi
authors.initials: T
authors.lastname: Watabe
authors.forename: Masaaki
authors.initials: M
authors.lastname: Aoki
authors.forename: Eiji
authors.initials: E
authors.lastname: Sugiyama
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Kato
authors.forename: Jun
authors.initials: J
authors.lastname: Hatazawa
mesh_terms: D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging; D055615:Electrical Equipment and Supplies; D006321:Heart / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D051379:Mice; D055100:Optical Fibers; D049268:Positron-Emission Tomography / Q000295:instrumentation*; D051381:Rats; D013997:Time Factors