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from the thesis works of Ignazio Vilardi Anna Palasciano Francesca Ciocia

Spatial & Energy resolutions (exp.& MC) for the Axial HPD-PET concept with YAP and LYSO crystals. from the thesis works of Ignazio Vilardi Anna Palasciano Francesca Ciocia. New 3D axial HPD-PET concept. p. PMTs. Arrays of long ( Lc ~ 10-15 cm ) crystal bars

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from the thesis works of Ignazio Vilardi Anna Palasciano Francesca Ciocia

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  1. Spatial & Energy resolutions (exp.& MC)for the Axial HPD-PET concept with YAP and LYSO crystals from the thesis works of Ignazio Vilardi Anna Palasciano Francesca Ciocia

  2. New 3D axial HPD-PET concept p PMTs Arrays of long (Lc~10-15 cm) crystal bars read out at both sides by segmented HPDs The 3D PET cameras Standard radial concept axis axis 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. A HPD-PET CAMERA MODULE • Array of 208 scintill.s (LSO, LYSO, YAP, LaBr3, n=1.8-1.9) • 16x13 crystals (3.2[Rx]x3.2[Ry]x150[Lc] mm3) • tx=51mm, ty=42mm  tX,Y>3·la (LSO)  e2g(⊥)~ 90% • with spacing: 4x4 mm2 Rx = 64 mm, Ry = 52 mm Rx Gain HPD : ~ 3.103 (Uop= 12 kV ) or 5.103 (Uop = 20 kV) Ry Lc • "Proximity focused“ HPDs • sapphire window (n~1.8): • (better light transmission) • (crystal-window refractive indices matching) • optical transport image 1 : 1 • segmented (4x4 mm2) silicon detector pads • (each crystal readout by its pad, no cross-talk) • each pad with integrated lecture electronics (2 VATA-Gp5)

  4. AFOV 25 cm PMT1 PMT2 LSO Dt = 7 ns 7.5 31 cm LSO 7.5 88 matrix (2x2 cm2)  4PMTs Dz (FWHM)~ 5 mm DV= (FWHM)~ 20 mm3 Lc =15mm~ 1 la e2g(⊥)~ 53% DE/E (511 keV) ~ 17% Heavy electronics (PSD) “Reference Radial PET”: TheHigh Resolution Research Tomograph (HRRT) (CTI, MPI, Karolinska …) K. Wienhard et al., IEEE Trans. Nucl. Sci. 49 (2002) 104–10 • ANGER LOGIC: a block seen by 4 PMTs • CM of signals in 4 PMTs  •  interac. point (x,y) of g • DOI (z) from PHOSWICH tecnique • Pulse Shape Discrimin. (PSD) Lc g z g x y • 8 panels with 9  13 blocks • 2  64 crystals per block • 120000 crystals 2.12.1x7.5mm3 • 936 (20x20 mm2) PMTs

  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, photofraction, 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 intrinsic energy resolution (~5% FWHM)

  6. 1) 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 (x,y) dimension • higher efficiency Double scatt. events in one module (Compton-photoel.) reconstruction • higher efficiency z y g g (Ry) x (Rx) HPD2 208 4 x 4 mm2 Si ‘pads’ centred on crystal matrix

  7. 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 (DOI) resolution worsens

  8. Lc, leff, No:KEY PARAMETERS OF THE HPD-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

  9. 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 50-150 mm3) • PMT H3164-10 (F=8mm, nw=1.47,bialkali) • B8850Quantacon(F=5cm,nw=1.47,bialkali) • linear translatorM-511(Phys.Instrum.)

  10. polished 3x3x100 mm3 YAP-LYSO comparison z=1 cm z = 5 cm z =9 cm 22Na source YAP+H3164-10 QL+QR (5cm)= 1692 ch photoelectric peak (511 keV) Compton ~ 10% ΔE/E(FWHM) ~ 14% LYSO+H3164-10 QL+QR (5cm)= 2295 ch • LYSO produces more light (pe’s) than YAP • LYSO has a higher photofraction, lower energy resolution than YAP

  11. effin polished(n2=1) 3x3x100 mm3 YAP-LYSO No/2 LYSO= 42.6±0.9 cm QL exp(-z/leff), ≈ n1/n2, n1/nW YAP= 20.8±0.4 cm 1/z2≈ n1/nW • LYSO more transparent (higher leff than YAP) • too high l-eff values (poor sz) both for LYSO and YAP

  12. 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 • at z=0: N0(teflon) > N0(polished) (diffusing wrapping) • leff (polished) / leff(teflon) = 1.9 • possibility to tune leff value with metal coatings • metal coating (n2) reduces No

  13. E/E, z, tdc(z=5cm) in coated 10cm YAP & LYSO (511 keV) vs leff YAP LYSO a) statistical b) phenomen. NO = 510±18 pe NO = 724±34 pe NO = 753±34 pe

  14. very low leff in a Lc=5 cm YAP with raw (smeared) lateral surfaces • no exp behaviour of Q1 (fermi function) • no coincident Q1-Q2 signals in a Lc = 10 cm YAP • very low leff , but dependent with z  • good sz but z-dependent, bad sE/E

  15. z , E/E in coated-smeared YAP & LYSO vs z, leff, Lc, Eg • crystal length worsens sz, does not influence much sE/E • worse sz and sE/E values at lower Eg • very low leff (raw lat.surf) values  Lc limited, z-dep. of sz

  16. Geant4 simulations for YAP long crystals + PMTs long and thin cylindrical crystal (n1, Nph/keV) lat.surface: polished, smeared (s), wrapped (nwrap), coated (nwrap,ik,t) polished bases coupled to PMTs (nwin, t,q.e.) Polar diagram of reflected-refracted scintillation photons I incident unpol. opt. photons A absorption R reflection T transmission D Lambertian diffusion SR diffuse reflect. (smear) ST diffuse transmiss.

  17. nwrapnwin (nwin=1.47) (nwrap=1.0) *refr.ind.match * nwrap does not change leff decreases No worsens E/E, z, t nwin decreases leff increases No improves E/E, z, t

  18. absorption diffusion smearing • absorp. & diffus. • similar effects • decrease leff • (diff. increases No) • improve z • worsen E/E, t • smearing • to be avoided • (N1 no more exp.)

  19. Geant4 reproduction of exp. results YAP + H3164-10 PMTs

  20. Geant4 predictions for engraved crystals • mechanical or laser ablation • engravings • (effects similar to absorp.) • decrease leff • improve spatial resol. • worsen energy-time resol. • & • high reproducibility • to the N0and leff • values of the many • HPD-PET crystals to be exp. proven

  21. HRRT vs. HPD-PET AFOV 25 cm 31 cm Full ring scanner A possible final configuration for a HPD-PET R = 170 mm • 12 modules • F =34 cm • Lc = 15 cm • 2496 crystals 3.2x3.2x150mm3 • 24 5” rect. HPDs • det.Vol. 3834cm3 • det.depth 41mm • DW/4p~ 0.165 • eTOT(LSO) (%) ~ 8.5 (ph) + 7.5 (Co-rec) • eTOT(LaBr3)(%) ~ 1.9 (ph) + 4.9 (Co-rec) • 8 panels 9x13 blocks • F =31 cm • AFOV = 25 cm • 120000 crystals 2.1x2.1x7.5mm3 • 936 PMTs 2x2cm2 • det.Vol. 3962cm3 • det.depth 15mm • DW/4p~ 0.344 • eTOT(LSO)(%) (exp) ~ 6.9 z y x

  22. HPD-PET(Lc=10cm) vs HRRT

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