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R. De Leo INFN, Sezione di Bari, I-70122 Bari, Italy

Scintillation studies for The Axial 3-D PET Concept HPD-PET project implemented by Wave Length Shifter Strip Hodoscope. HPD-PET ---> AX-PET. R. De Leo INFN, Sezione di Bari, I-70122 Bari, Italy. the axial HPD-PET concept. p. PMT. Arrays of long ( Lc ~ 10-20 cm ) crystal bars

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R. De Leo INFN, Sezione di Bari, I-70122 Bari, Italy

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  1. Scintillation studies for The Axial 3-D PET Concept HPD-PET projectimplemented by Wave Length ShifterStrip Hodoscope HPD-PET ---> AX-PET R. De Leo INFN, Sezione di Bari, I-70122 Bari, Italy

  2. the axialHPD-PET concept p PMT Arrays of long (Lc~10-20 cm) crystal bars read out at both sides by segmented HPDs The 3D PET cameras Standard radial PET concept PET HPD-PET Many rings of crystal–photodetector blocks radially displaced Lc =1.5-3cm Concept made possible by CERN development of rectangular segmented 5‘’ HPDs with integrated self-triggering electronics

  3. HPD-PET ADVANTAGES OF THE AXIAL HPD-PET CONCEPT High Granularity  exact reconstruction of the g interaction point (no parallax error) HPD1 • x,y from fired scintillator • σ(x,y) = 3.2 mm/√12= 0.92 mm • Dx,Dy (FWHM) = 2.2 mm • z (DOI) from the ratio of the photoelectrons • detected at the two crystal ends • σ(z) linked to the scint. choice Reduced # of photodet., scint., electr.  (12 module PET: only 24 HPDs) • No limit to module radial dimension • higher efficiency Double scatt. events in one module (Compton-photoel) reconstruction • higher efficiency J. Séguinot et al.,Nuovo Cimento C, 29 (2006)429-463 z y g g (Ry) x (Rx) HPD2 208 4 x 4 mm2 Si ‘pads’ centred on crystal matrix

  4. 2) ADVANTAGES OF THE AXIAL HPD-PET CONCEPT possibility to reconstruct the int. point of part of g’s that suffers a double (Compton + photoelectric) event in the same module COMPTON + PHOTOELECTRIC events- ~ 25% Compton events (50 keV [energy cut] < E < 170 keV) followed by a photoelectric one in the same module can unambiguously be reconstructed detection efficiency increases but spatial resolution worsens

  5. YAP:Ce LSO:Ce LuAP:Ce LaBr3:Ce Density ρ (g/cm3) 5.55 7.4 8.34 5.3 7.13 Effective atomic charge Z 32 66 65 75 46.9 Scintillation light output (photons / MeV) 18000 23000 ~10000 ~61000 ~9000 wavelength lmax of max. emission (nm) 370 420 370 356 480 Refractive index n at lmax 1.94 1.82 1.95 ~2.15 ~1.88 Bulk light abs. length lbulk (cm) at lmax ~20 ~40 Principal decay time (ns) 27 40 18 300 30±5 Mean γ atten. length la at 511keV (mm) 22.4 11.5 10.5 ~11.6 ~20 Photo fraction at 511 keV (%) 4,5 32.5 30.5 41.5 15 Energy resolution (FWHM) at 663 keV 4.5 8 2.9 Inorganic Scintillation crystals • Criteria to be taken into account:light yield, absorption length, photo fraction, self absorption, decay time, availability, machinability, price. BGO LSO (LYSO) is the most interesting crystal scintillator : fast (40 ns), short att. length (~12mm) at 511keV, high photofraction (32%), not hygroscopic, but high energy resolution (8% FWHM)

  6. PROOF of the HPD-PET CONCEPT with YAP and LYSO crystals and PMTs  BaF2 (used with a 22Nasource)  Pb collimator Pb +source YAP (Preciosa Co) LYSO (Photonic Materials) (3.2 x 3.2 x 100 mm3) PMT H3164-10 (F=8mm, 1250 V) linear translatorM-511(Phys.Instrum.)

  7. HPD-PET Lc, leff, No:KEY PARAMETERS OF THEHPD-PET CONCEPT • Lc:crystal length • leff:attenuation length of scint. photons • 1/leff = 1/(lbulk* cos q) + c’/(cabs) • No:light yield, p.e.’s (511keV g) in a Lc~0 crystal • (nph/keV, sci.ph.transport, q.e. & wind. of photodet.) HPD1 Z σz, σE/E, σt: (only statistical) g cabs g q a) crystal axial length (Lc) worsens all resolutions HPD2 limit of Lc: 10 ~15cm b) light yield (No) improves all resolutions c) contrasting effects ofleff on σz& σE/E, σt • optimize leff value by wrapping or coating the crystal lateral surface

  8. Typical pulses from LYSO bars

  9. eff in polished 3x3x100 mm3 YAP-LYSO LYSO= 42.6±0.9 cm QL YAP= 20.8±0.4 cm • LYSO more transparent (higher leff) than YAP • too high l-eff values (poor sz) both for LYSO and YAP

  10. Crystal wrappings or metal-coatings change light attenuation length of a YAP (3.2 x 3.2 x 100 mm3) No/2 polished QL best solution I.Vilardi et al.,NIM A564(2006)506 • at z=0 Q(teflon) > Q(polished): slight increase of No • l (polished) / l(teflon) = 1.9 • possibility to tune l-eff value with metal coatings • metal coating reduces No

  11. HPD1 HPD1 z y x HPD2 HPD2 N1 HPD-PET WLS-HPD-PET New WLS-HPD-PET concept (proposed by D.Schinzel) N2 HPD-PET concept WLS strip width w = 3 mm, σz ≤ w/√12 =0.9 mm A. Braem et al.,NIM A580(2007)1513

  12. Detector WLS-HPD-PET WLS-HPD-PET concept HPD HPD HPD HPD two PET modules, one WLS hodoscope

  13. SETUP for WLS-HPD-PET Test LYSO + 2WLS readout by PMTs

  14. Typical pulses from WLS strips bars tWLS =10 ns tLYSO =30 ns Sum of channels 1 and 2

  15. charge distribution of the sum of two WLS Edep= 350 keV Charge distribution : sum of the two WLS strips response. 40 pe’s (ADC counts)

  16. charges on 2 LYSO bars 3 mm Strip# 1 Strip # 2 WLS WLS WLS LYSO at z = 64 mm (centre of strip #1) 65% of charge on strip #1, 35% on strip#2

  17. Scintillation position (DoI) reconstruction Edep= 350 keV Q1 = 0 Zrec Q2 = 0 WLS Q1 Q2 LYSO Zrec = c + m (Q2 – Q1) / (Q2 + Q1) m = 0.9 (# 1) is due to a different det.eff. of the two WLS strips. c = constant

  18. Zrec distribution from two WLS charges Edep=350 keV Ztrue = 60.8 mm Zrec=60.83±1.24 σZvaries as 1/√E, i.e.~ 1 mm at 511 keV Z (mm)

  19. From our publication in Il Nuovo Cimento Vol. 29 C,N. 4 FWHM values WLS-HPD-PET LYSO ~2.2 ~2.2 2.1 ~ 9 mm3 This is ~ physical limit due to positron range and gamma acolinearity

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