HPD based PET scanner protoype ============================== Meeting at CERN 24 April, 2002 Present: E. Chesi, F. Cusanno, F. Garibaldi, Z. Habib, C. Joram, E. Nappi, J. Seguinot, P. Weilhammer Summary ======= Following analytical calculations and first Monte-Carlo simulations the following project has been tentatively agreed on: The aim is to develop and construct a PET scanner dedicated to brain research. The free inner diameter of the scanner is ca. 30-32 cm. The first prototype phase foresees to develop at least 2 PET camera modules. Each module comprises a matrix of scintillator crystals, read out by 2 HPD tubes. The following design parameters have been chosen as a working hypothesis: ------------------------------------------------------------------------- - Scintillator material: Ce doped YAP or LSO. LuAP will be considered at a later stage depending on its availability. - Scintillator geometry: 12 x 18 scintillator crystals form a matrix. Each crystal has the dimensions 3.2 x 3.2 x 100 mm. Both ends are polished spherically to form a lens with radius of curvature of 6 mm. All scintillator surfaces are polished to optical quality. Quotes should be obtained for 450 crystals both for YAP and LSO. LSO crystals of 100 mm length may need to be formed by glueing two 50 mm long crystals. The scintillators are mounted with a gap of 0.8 mm (i.e. the pitch of the scintillator matrix is 4 mm). The gaps between the crystals are masked on the level of the lens (e.g. by means of a spacer grid). - Photodetectors: While for a final system rectangular HPD tubes bring significant advantages, round ceramic tubes are foreseen for this protoype scanner. In the following this HPD tube is called PCR5 (for "PET Ceramic Round 5-inch"). PCR5 is a proximity focused HPD with a K2CsSb (bialkali) photocathode. QE ca. 20-25% at 390 nm. It makes use of the existing round base plates of 5" diameter (possibly the number of vaccuum feedthroughs may need to be increased for the VATA-GP3 chips). The silicon sensor has 12 x 18 (216) pads of size 4.0 mm, matched to the crystal matrix. The overall active sensor size is 48 x 72 mm. The base plate carries a ceramic hybrid on which 2 VATA-GP3 chips and the rectangular silicon sensor are mounted. The ceramic tube body is equipped with a round (or rectangular) sapphire window. The window is sealed to the ceramic body by a ceramic-metal brazing technique involving an Niobium ring. In order to avoid E-field inhomogeneities caused by the Niobium ring, the window should exceed the sensor dimensions on all sides by about 10 mm. The thickness of the window is 1.8 mm. PCR5 has 1 or 2 round electrodes, integrated in the tube body. The distance between the photocathode and the silicon sensor should be minimised in the interest of a small point spread function. Current baseline: 50 mm. Participating institutes (contact person) and initial areas of activity: ------------------------------------------------------------------------ Bari (E. Nappi) Scintillator crystal array (assembly, characterisation). Together with Rome CERN (P. Weilhammer) HPD + Silicon + readout, concept + simulations HUG (H. Zaidi) Reconstruction / correction / display software Univ. Geneva (A. Clark) Simulation of gamma interaction (Geant4) Rome (F. Garibaldi) Simulations of gamma and visible photons (EGS 4 + WavePro) Possible future collaborators: Ohio State University, Ljubljana Uncovered area: Mechanics (gantry) and integration. The company CTI may be contacted at a later stage (once the patent application is filed) to discuss a possible involvement. Ideally CTI would provide LSO crystals and the gantry. Financing --------- A first rough cost estimate for the above described project ends up at 200 - 250 kCHF. The following initial (year 2002) contributions are foreseen: Bari 10 kCHF Rome 10 kCHF CERN HPD project 30 kCHF Univ. Geneva 10 kCHF Two preliminary applications have been sent to international and national foundations supporting research in this area. Full applications by invitation only if passing the first evaluation by experts (June/July 2002). An application to FNRS (Fonds national suisse de la recherche scientifique) in preparation. The CERN ETT division has expressed the intention to substantially support the PET HPD project.