title: Development of a novel depth of interaction PET detector using highly multiplexed G-APD cross-strip encoding.
abstract: OBJECTIVE
  The aim of this study was to develop a prototype PET detector module for a combined small animal positron emission tomography and magnetic resonance imaging (PET/MRI) system. The most important factor for small animal imaging applications is the detection sensitivity of the PET camera, which can be optimized by utilizing longer scintillation crystals. At the same time, small animal PET systems must yield a high spatial resolution. The measured object is very close to the PET detector because the bore diameter of a high field animal MR scanner is limited. When used in combination with long scintillation crystals, these small-bore PET systems generate parallax errors that ultimately lead to a decreased spatial resolution. Thus, we developed a depth of interaction (DoI) encoding PET detector module that has a uniform spatial resolution across the whole field of view (FOV), high detection sensitivity, compactness, and insensitivity to magnetic fields.
  
  
  METHODS
  The approach was based on Geiger mode avalanche photodiode (G-APD) detectors with cross-strip encoding. The number of readout channels was reduced by a factor of 36 for the chosen block elements. Two 12 × 2 G-APD strip arrays (25 μm cells) were placed perpendicular on each face of a 12 × 12 lutetium oxyorthosilicate crystal block with a crystal size of 1.55 × 1.55 × 20 mm. The strip arrays were multiplexed into two channels and used to calculate the x, y coordinates for each array and the deposited energy. The DoI was measured in step sizes of 1.8 mm by a collimated (18)F source. The coincident resolved time (CRT) was analyzed at all DoI positions by acquiring the waveform for each event and applying a digital leading edge discriminator.
  
  
  RESULTS
  All 144 crystals were well resolved in the crystal flood map. The average full width half maximum (FWHM) energy resolution of the detector was 12.8% ± 1.5% with a FWHM CRT of 1.14 ± 0.02 ns. The average FWHM DoI resolution over 12 crystals was 2.90 ± 0.15 mm.
  
  
  CONCLUSIONS
  The novel DoI PET detector, which is based on strip G-APD arrays, yielded a DoI resolution of 2.9 mm and excellent timing and energy resolution. Its high multiplexing factor reduces the number of electronic channels. Thus, this cross-strip approach enables low-cost, high-performance PET detectors for dedicated small animal PET and PET/MRI and potentially clinical PET/MRI systems.
authors.affiliation: Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tübingen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Kolb
authors.affiliation: Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tübingen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Parl
authors.affiliation: Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tübingen, Germany and Department of Empirical Inference, Max Planck Institute for Intelligent Systems, 72076 Tübingen, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Mantlik
authors.affiliation: Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tübingen, Germany.
authors.forename: C C
authors.initials: CC
authors.lastname: Liu
authors.affiliation: Max Planck Institute for Physics, Föhringer Ring 6, 80805 München, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Lorenz
authors.affiliation: Department of Physics, Technische Universität München, 85748 Garching, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Renker
authors.affiliation: Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University, 72076 Tübingen, Germany.
authors.forename: B J
authors.initials: BJ
authors.lastname: Pichler
mesh_terms: D000818:Animals; D055615:Electrical Equipment and Supplies; D004867:Equipment Design; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods; D064847:Multimodal Imaging / Q000295:instrumentation / Q000379:methods; D049268:Positron-Emission Tomography / Q000295:instrumentation* / Q000379:methods; D013995:Time