New Scintillating Crystals for PET Scanners

1. New Scintillating Crystals for PET Scanners Paul Lecoq, CERN Geneva, Switzerland Pasadena, CALOR2002, 26 March 2002

2. Requirements for HEP crystal calorimeters Crystals High density (> 6 g/cm3) Fast emission (< 100ns), visible spectrum Moderate to high light yield High radiation resistance Photodetectors Compact High quantum efficiency and high gain High stability Readout electronics Fast shaping Low noise Sofware Handling of high quantity of data General design Compact integration of a large number of channels ( >> 10’000) Requirements for PET and SPECT scanners Crystals High density (> 7 g/cm3) Fast emission (< 100ns), visible spectrum High light yield Moderate radiation resistance Photodetectors Compact High quantum efficiency and high gain High stability Readout electronics Fast shaping Low noise Sofware Handling of high quantity of data General design Compact integration of a large number of channels ( >> 10’000) A Technology Transfer example from High Energy Physics to Medical Imaging Technology transfer Technology transfer Technology transfer Technology transfer Technology transfer

3. Photoabsorption Coefficient @511 KeV > 0.2cm-1 LY > 104 Ph/MeV Decay Time < 100ns Known materials New Scintillators for PET applications ??????????? To be discovered ??????????? ??????????? Less light but cheap ???????????

4. LuAP Development • First studies in 94 • Lempicki et al. • Derenzo et al., • Korzhik & Crystal Clear • First attempts to grow LuAP crystals in 95 • CRYTUR (Czech republic) with Crystal Clear • A. Petrossian (Armenia) with Crystal Clear • AIRTRON (USA) with Lempicki • Detailed studies from 94 to 99 by the Crystal Clear collaboration • Lausanne-Prague-Crytur (Swiss Fonds National) • Lyon LPCML-Ashtarak (CNRS) • Engineering of LuAP technology: starting in 2000 • Bogoroditsk (Russia) with CERN-ISTC support

5. 2000-2001: Feasibility study CERN 50K$ 2001-2002: Industrial phase CERN 250K$ $ $ $ $ ISTC #1489 50K$ ISTC #2039 525K$ $ x 2 x 3 $ $ $ Bogoroditsk Bogoroditsk LuAP technology development • CERN-ISTC cooperation • Conversion program for former Soviet Union militaro-industrial complex funded by the G8 • Very positive experience with the Bogoroditsk Plant for the production of 100 tons of Lead Tunstate crystals for the CERN CMS experiment (20M$ project) • New ISTC project (200K$) recently approved for LuAP technology development in Ashtarak

6. A very high precision in the stoechiometry of the starting raw material is required A very high precision and stable heating system is required in the oven to keep the temperature in the range ±3°C A good control of thermal leaks and well designed geometry is required to maintain the melt temperature in the range ±3°C everywhere in the crucible Lu2O3- Al2O3 Phase diagram

7. LuAP technology developmentBogoroditsk, Russia LuAP, Crystal Clear, Bogoroditsk, August 2000

8. LuAP technology developmentBogoroditsk, Russia

9. Results - Light Output and Energy Resolution Results by C. Kuntner • Light output • 1510 - 2370 phe/MeV (± 70) • QE~25% 6000 - 9500 ph/MeV (± 500) • energy resolution • 10 - 21% • when poor energy resolution double or triple peaks inhomogeneities in the crystal

10. A very high precision in the stoechiometry of the starting raw material is required A very high precision and stable heating system is required in the oven to keep the temperature in the range ±3°C A good control of thermal leaks and well designed geometry is required to maintain the melt temperature in the range ±3°Cevery where in the crucible Addition of some quantity of Yttrium helps in stabilizing the perovskite phase Lu2O3- Al2O3 Phase diagram

11. Photoelectric absorption coefficient @511KeV of the (Lu+Y)Al2O3 system, compared to GSO and LSO Photoefficiency @511KeV of the (Lu+Y)Al2O3 system as a function of the sample thickness The (Lu+Y)Al2O3 system

12. Seeded Lu70Y30AP:Ce

13. Seeded Lu70Y30AP:Ce

14. Ce4+ suppression

15. Ce4+ suppression

16. LSO Crystal Results-Light Yield • LuYAP Crystal

17. Results - Different Sources • Light output (crystal 1098) • 2030 (± 100) Npe/MeV • QE~25%  8100 (± 400) Nph/MeV

18. Results - Energy resolution • LuYAP Horizontal • 7.7 (± 0.4) % FWHM • LSO Horizontal • 8.6 (± 0.4) % FWHM

19. Results - Energy resolution / Light Yield • Theory • Intrinsic resolution • sc ~ 2.7% • YAP:Ce sc = 1.3 ± 0.5% • CsI(Tl) sc = 4.1 ± 0.2% • NaI(Tl) sc = 5.7 ± 0.2% • LSO sc = 7.6 ± 0.5% Moszynski et al, Nucl. Instr. and Meth. A 421 (1999) 610-613

20. Results - Light Pulse Shape • 3 exponential fit • fast = 23.4 (± 2) ns (38%) • med = 100 (± 30) ns (23%) • slow ~ 500 (± 70) ns (39%) • 2 exponential fit • fast = 27.8 (± 2) ns (48%) • slow ~ 320 (± 25) ns (52%)

21. Photoabsorption Coefficient @511 KeV > 0.2cm-1 LY > 104 Ph/MeV Decay Time < 100ns Known materials New Scintillators for PET applications ??????????? To be discovered ??????????? ??????????? Less light but cheap ???????????

22. Search for heavy cations associated to rare earth • Investigate materials based on Hf 4+ and Ba 2+ , with 5p6 outer shell, combined with Lutetium or another rare earth • Band gap must be larger than 5eV to allow 5d-4f transition of Ce 3+ • 4f level of must be close enough to top of valence band to allow easy hole trapping • 5d level of must be far enough from bottom of conduction band to avoid electron delocalization at room temperature

23. Samples selection and preparation • Prepared from 5N oxydes, blended, and annealed in several steps at 1400°C • After the second or third annealing X-Ray diffraction showed at least 50% of the desired phase in compound • All materials are 1% at. Cerium doped

24. Hafnium and Barium based compounds • No observed X-Ray excited luminescence for undoped materials • No luminescence for Ce doped BaLa2O4 • Bright and fast luminescence for all other components >2000 ph/MeV

25. Excitation and emission spectra

26. Excitation and emission spectra

27. Photoabsorption Coefficient @511 KeV > 0.2cm-1 LY > 104 Ph/MeV Decay Time < 100ns Known materials New Scintillators for PET applications ??????????? To be discovered ??????????? ??????????? Less light but cheap ???????????

28. Eg= 59 MeV s/E=7% central detector relative time between two adjacent modules counts 850 MeV time 5 - time 6 [a.u.] time resolution per module s = 130 ps PWO Low energy and timing resolution(From R. Novotny et al)

29. PWO with a LY of ≥ 100Pe/MeV could become attractive for low cost full body PET scanners for cancer screening Non radiative losses in PWO Temperature quenching of WO42- luminescence: SJR 6 Migration quenching of WO42- luminescence Redistribute non radiative losses on a well selected acceptor with A weak Coulomb interaction with WO42- centers A strong e- capture cross section How to improve PWO Light Yield

30. 1- PWO:Mo MoO42- has a very high e- capture cross section MoO43- is metastable and produces slow components and afterglow MoO42- luminescence is also temperature quenched PWO Light Yield improvement • 2- PWO:Mo, La • The shallow WO43- + La centre is an additional radiating centre • Prevents e- to be trapped by deep Mo centres • Suppresses afterglow and large part of slow components

31. 68% light In 100ns 16pe/MeV 27pe/MeV 56pe/MeV PWO Light Yield improvement P. Lecoq, M. Korzhik, Proc. 1999 IEEE NSS/MIC, Seattle A. Annenkov, M. Korzhik, P. Lecoq, NIM A 450 (2000), 71-74

32. M.Kobayashi et al, Proc. SCINT2001, Chamonix, France, sept 2001 M.Kobayashi et al, NIMA 434 (1999) 412-423 R. Zhu, Proceedings IEEE2000, Lyon PWO Light Yield improvement

33. Conclusions • LuAP:Ce • Lu0.7Y0.3AP:Ce production is now stabilized. One production line ready • R&D in progress for increasing Lu fraction up to at least 90% this year on a second line • R&D on a third line to understand LuAP:Ce (100%Lu) production issues: technology, yield, cost • New materials based on 5p6 outer shell cations, combined with a rare earth • Promising results for several Hf and Ba compounds • Bright and fast luminescence in the green • Lead Tungstate with increased Light Yield • A light yield ≥ 100 pe/MeV is probably not out of reach • Its very high Zeff (similar to BGO) and low cost would then make this material attractive for lower cost full body machines for cancer screening