Optimizing timing resolution of SiPM sensors for use in...
Transcript of Optimizing timing resolution of SiPM sensors for use in...
NDIP – 20 June 2008
Optimizing timing resolution of SiPM sensors for use in
TOF-PET detectors
Ruud Vinke
NDIP – 20 June 2008
Overview
• Principle of TOF-PET• Relevant PET detector requirements• SiPM timing characterization
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The principle of TOF-PET
500 ps → 7.5 cm
uniform probability on line-of-response (LOR)
Δ x=c Δ t2
Moses, W. W., IEEE Trans. Nucl. Sci., vol. NS-50, pp. 1325-1330, 2003
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2 line sourcesinside water cylinder
TOF-PET: a simulated example
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TOF-PET: a simulated exampleno TOF TOF
500 ps FWHM
4 cm
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TOF-PET: a simulated examplesame resolution
improved contrast
non-TOF
TOF
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PET image deterioration
parallax error
incorrectLOR
measuredepth-of-interaction (DOI)
Comptonscattering
Compton scattering
select full-energy peakenergy resolution < 7 %
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Conventional detector configuration
Anger logic
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Monolithic scintillator with photosensor array
Statistics based reconstruction, e.g.:
- Nearest neighbour estimation- Neural network estimation- Maximum likelihood estimation
DOI
M. C. Maas, et al., IEEE Trans. Nucl. Sci.,vol. NS-53, pp. 1071-1077, 2006
Gamma photon entry point estimation -> automatic correction for parallax error
DOI estimation -> correction for DOI-induced time dispersion
(In cooperation with TU Delft)
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Scintillator materialLaBr3:
• sufficient energy resolution• good timing properties
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Photodetector
SiPM:• good timing properties
• MRI compatibility
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Acqiris digitizer
• DC282 high-speed digitizer• 10-bit resolution• 8 GS/s sampling rate
(4 GS/s for 2 ch acquisition) • 2 GHz bandwidth• 50 Ohm input impedance• 1 ps jitter
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Timing setup
• Hamamatsu PLP10-40 laser• 405 nm peak wavelength• 70 ps pulse width
• Hamamatsu MPPC 25U, 50U, 100U
• Hamamatsu PLP10-40 laser• 405 nm peak wavelength• 70 ps pulse width
• High bandwidth voltage preamp
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SiPM pulse tracesMPPC 50U; Vop 70.49 V
Afterpulse filtering
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SiPM risetime spectrum
1.21 ns peak
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SiPM: single photoelectron sensitivity
1
2
3
4
no. of photoelectrons
MPPC 50U; Vop 69.51 V
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Breakdown voltage determination
2 phe
1 phe
3 phe
4 phe
MPPC 50U
Breakdown voltage
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Time pickoff procedure
CF30%
Time mark
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SiPM timingMPPC 50U
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Single photoelectron timingMPPC 50U
100 ps single photon sigma time res.
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Coincidence measurements
• 2x2x8 mm3 LYSO crystal• Hamamatsu SiPM with 1 mm2 effective area• Na-22 source → 511 keV anti-parallel gamma emission• Optical coupling needs to be improved
~180 ps fwhm time resolution
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Coincidence timing resolution (preliminary)
MPPC 100U – Vop 69.77 V (1.14 V above breakdown )
� 600 ps fwhm
1 phe 2 phe
Nr incident photons: ~400
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Photon detectionefficiency Saturation
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Coincidence timing resolution (preliminary)
MPPC 100U – Vop 69.77 V (1.14 V above breakdown )
� 600 ps fwhm
1 phe 2 phe
Nr incident photons: ~400PDE 100U: ~50%→ ~200 photoelectrons→ ~85 pixels fired
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GATE/GEANT4 simulation of optical transport in crystal
• GEANT4 source code adapted to include effect of scintillation rise time on timing:
• Included detailed physics properties of scintillation emission spectrum; gamma absorption length spectrum; crystal surface reflectivity; SiPM fill factor; etc
Shao, Y. P., Phys. Med. Biol., vol. 52, pp. 1103-1117, 2007
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Summary
• ~ 100 ps single photon sigma timing resolution for Hamamatsu SiPM devices
• Pulse digitization allows flexible determination of timing properties
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Outlook
• SiPM photosensor array on monolithic LaBr3 crystal
• MLE determination of 3D gamma interaction position for correcting DOI induced time dispersion