New Scintillating Crystals for PET Scanners

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New Scintillating Crystals for PET Scanners

• Paul Lecoq, CERN Geneva, Switzerland
• Pasadena, CALOR2002, 26 March 2002

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A Technology Transfer example from High Energy
Physics to Medical Imaging

• Requirements for HEP crystal calorimeters
• Crystals
• High density (gt 6 g/cm3)
• Fast emission (lt 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
  ( gtgt 10000)

• Requirements for PET and SPECT scanners
• Crystals
• High density (gt 7 g/cm3)
• Fast emission (lt 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
  ( gtgt 10000)

Technology transfer
Technology transfer
Technology transfer
Technology transfer
Technology transfer
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New Scintillators for PET applications
??????????? To be discovered ???????????
??????????? Less light but cheap ???????????
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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

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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

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Lu2O3- Al2O3 Phase diagram

• 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 3C
• A good control of thermal leaks and well designed
  geometry is required to maintain the melt
  temperature in the range 3C everywhere in the
  crucible

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LuAP technology developmentBogoroditsk, Russia
LuAP, Crystal Clear, Bogoroditsk, August 2000
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LuAP technology developmentBogoroditsk, Russia
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Results - Light Output and Energy Resolution
Results by C. Kuntner

• Light output
• 1510 - 2370 phe/MeV ( 70)
• QE25
• 6000 - 9500 ph/MeV ( 500)
• energy resolution
• 10 - 21
• when poor energy resolution
• double or triple peaks
• inhomogeneities in the crystal

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Lu2O3- Al2O3 Phase diagram

• 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 3C
• A good control of thermal leaks and well designed
  geometry is required to maintain the melt
  temperature in the range 3Cevery where in the
  crucible
• Addition of some quantity of Yttrium helps in
  stabilizing the perovskite phase

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The (LuY)Al2O3 system

• Photoefficiency _at_511KeV of the (LuY)Al2O3 system
  as a function of the sample thickness

• Photoelectric absorption coefficient _at_511KeV of
  the (LuY)Al2O3 system, compared to GSO and LSO

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Seeded Lu70Y30APCe
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Seeded Lu70Y30APCe
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Ce4 suppression
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Ce4 suppression
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Results-Light Yield

• LSO Crystal

• LuYAP Crystal

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Results - Different Sources

• Light output (crystal 1098)
• 2030 ( 100) Npe/MeV
• QE25
• ? 8100 ( 400) Nph/MeV

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Results - Energy resolution

• LuYAP Horizontal
• 7.7 ( 0.4) FWHM

• LSO Horizontal
• 8.6 ( 0.4) FWHM

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Results - Energy resolution / Light Yield

• Theory

• Intrinsic resolution
• ?sc 2.7
• YAPCe ? 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
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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)

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New Scintillators for PET applications
??????????? To be discovered ???????????
??????????? Less light but cheap ???????????
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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

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Samples selection and preparation

• Prepared from 5N oxydes, blended, and annealed in
  several steps at 1400C
• 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

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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 gt2000 ph/MeV

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Excitation and emission spectra
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Excitation and emission spectra
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New Scintillators for PET applications
??????????? To be discovered ???????????
??????????? Less light but cheap ???????????
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PWO Low energy and timing resolution (From R.
Novotny et al)
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How to improve PWO Light Yield

• 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

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PWO Light Yield improvement

• 1- PWOMo
• MoO42- has a very high e- capture cross section
• MoO43- is metastable and produces slow components
  and afterglow
• MoO42- luminescence is also temperature quenched

• 2- PWOMo, 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

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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
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PWO Light Yield improvement
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Conclusions

• LuAPCe
• Lu0.7Y0.3APCe production is now stabilized.
• One production line ready
• RD in progress for increasing Lu fraction up to
  at least 90 this year on a second line
• RD on a third line to understand LuAPCe
  (100Lu) 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