Silicon Photomultiplier as an Alternative for APD in PET/MRI Applications

NSS-MIC October 2008

Antoni Nassalski, M. Moszyński, A. Syntfeld-Każuch, Ł. Świderski, T. Szczęśniak, D. Wolski, T. Batsch, J. Baszak*)

The Sołtan Institute for Nuclear Studies, PL 05-400 Otwock-Świerk, Poland

*) Hamamatsu Photonics Deutschland GmbH, Polish Office

Antoni Nassalski – Silicon Photomultiplier as an Alternative for APD in PET/MRI Applications, 2/11

Development of Multi Pixel Photon Counters (MPPC), a solid state photodetector known as the Silicon PhotoMultiplier (SiPM), with significant advantages such as high gain, fast timing, compactness and insensitivity to magnetic field, suggest to characterize the performances of this photodetector.

The MPPC is a new type of photon-counting device made up of multiple avalanche photodiode (APD) pixels operating in Geiger mode [1-4].

The aim of this work was to characterize: •the MPPC detectors, using a laser diode pulser,•the MPPC coupled to a 3x3x20 mm3 LSO pixel crystal,•fired number of pixels, and the amount of detected light, •the time & energy resolution for 511 keV annihilation

quanta,•the non-proportionality of the light yield.

Motivations

Experimental DetailsHamamatsu MPPC parameters

[2] Type S10362-

33-025CS10362-33-050C

Active area3×3 mm2 3×3 mm2

Number of pixels 14400 3600

Pixel size 25x25 m 50x50 mFill factor 30.8 % 61.5 %Gain 2.75 x 105 7.5 x 105

Spectral resp. range 270 - 900 nm

Q.E. 70% at 400 nmOperating voltage 70 ± 10 V

Dark counts 5 McpsCapacitance 320 pF

The MPPC were illuminated by a red laser diode type HL6501MG, Opnext, Japan.

The signal was sent to the:

Charge sensitive preamplifier,Ortec 460 Delay Line Amplifier, Multichannel analyzer Tukan 8K [exhibition Booth 42].

Antoni Nassalski – Silicon Photomultiplier as an Alternative for APD in PET/MRI Applications, 3/11

Properties of the LSO crystal [5]

Light output [ph/MeV] 31000Peak emission [nm] 420Decay time [ns] 40 – 47Refr. Index 1.82Density [g/cm3] 7.4Manufacturer CTI

Results The MPPC performance

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The signal from the MPPC is proportional to the number of the detected photons [1]-[4].

If two or more photons triggers one pixel then, the photon detection linearity lowers because the number of incident photons becomes larger then the number of fired pixels.

The individual photon peaks are separated.

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The deviation from the linear dependence - the solid line, calculated for the infinite number of pixels in the MPPC.

The nonlinear response of MPPC reflected by a deviation of FWHM from the theoretical values calculated for a perfectly linear photodetector.

The range of linearity is more extended in case of MPPC with higher number of active pixels

The increase of the gain for about 70%, (0.3 V bias voltage change), does not affect the pulse height resolution.

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Antoni Nassalski – Silicon Photomultiplier as an Alternative for APD in PET/MRI Applications, 7/11

a) Number of photoelectrons, phe/MeV, 137Cs (662keV),e) 2x2x15 mm3 LSO crystal coupled to Hamamatsu S8550 APD array [7],

Gamma-ray Spectrometry

The energy spectra of single photoelectron and 137Cs, measured for LSO crystal with 14400 pixels Hamamatsu MPPC.

Photodetector Number of pixels Nphe

a) E/E [%] QE (PMT) PDE (MPPC)

Light output[ph/MeV]

MPPC 025C 14400 1550±80 14.8±0.6 8.6±1% 180001800MPPC 050C 3600 1700±90 14.0±0.6 9.2±1% 180001800PMT XP2020Q - 3950±200 11.3±0.5 21.9% 180001800APD S8550 e) - 7010±350 12.8±0.6 - -

The light output of the LSO measured with the XP2020Q PMT, allows estimate the PDE of the tested MPPC.

The estimated PDE is much lower than expected (based on the QE and fill factor) 43 % for 14400 and 22 % for 3600 pixels devices.

Lower number of pixelslimits the detector linearity.

The non-proportionality for LSO measured with Hamamatsu MPPC

The energy resolution for LSO measured with Hamamatsu MPPC

The En. Res. measured with the PMT is superior thanks to a larger number of photoelectrons produced at the photocathode.

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Antoni Nassalski – Silicon Photomultiplier as an Alternative for APD in PET/MRI Applications, 9/11

Time Resolution Study Photodetector Number

of pixelsNphe

a) δt [ps] δt*N1/2 x 103

MPPC 025C 14400 790±40 850±40 23.9±1.2MPPC 050C 3600 870±40 780±40 23.0±1.2

PMT XP2020Q - 2000±100 240±10 10.7±0.6APD S8550 b) - 3180±160 2150±110 -a) Number of photoelectrons for 511 keV,b) 2x2x15 mm3 LSO crystal coupled to Hamamatsu S8550 APD array [7].

The best time resolution was measured with the PMT, 3 times better than with the MPPCs and superior to the APD array due to its dark noise.

The time resolution normalized to the number of photoelectrons reflects a better timing capabilities of the PMTs in comparison to the MPPCs. This is the effect of a slow rise time and a large capacitance of the MPPCs.

Conclusions• The number of fired pixels and its relation to the pulse

height resolution were determined and the photon detection efficiency for the light from LSO crystal was estimated,

• A high number of pixels in the detector assure a good linearity of the response to the light and a acceptable energy resolution,

• A slow output pulse is associated with a high capacitance of the devices, which limits the time resolution,

• The studies showed that the new Hamamatsu S10362-33-025C / 050C MPPC can be applied in nuclear medicine (for PET/MRI instrumentation as alternative to APD arrays or commonly used PMTs and in high energy physics.

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References

Silicon Photomultiplier as an Alternative for APD in PET/MRI Applications A. Nassalski, M. Moszyński, A. Syntfeld-Każuch,

Ł. Świderski, T. Szczęśniak, D. Wolski, T. Batsch, J. Baszak

Submitted to IEEE Trans. Nucl. Sci.

[1] P. Buzhan et al., “Silicon Photomultipliers and its possible applications”, Nucl. Instr. and Meth. A 504, pp. 48-52, 2003.

[2] www.sales.hamamatsu.com[3] G. Llosá, et al. “Silicon Photomultiplier and SiPM matrices as photodetectors in nuclear

medicine”, 2007 Nucl. Sci. Symp. Conf. Rec., pp. 3220- 3223, N14-4.[4] C. Piemonte, et al. “Recent developments on silicon photomultipliers produced at FBK-

irst”, 2007 Nucl. Sci. Symp. Conf. Rec., pp. 2089-2092, N41-2.[5] C. L. Melcher and J.S. Schweitzer, „Cerium doped lutetium oxyorthosilicate: A fast efficient

new scintillator”, IEEE Trans. Nucl. Sci., vol. 39, 502-505, 1992.[6] M. Moszyński, M. Kapusta, M. Mayhugh, D. Wolski, S.O. Flyckt, "Absolute Light Output

of Scintillators”, IEEE Trans. Nucl. Sci., vol. 44, no. 3, pp 1052-1061, June 1997.[7] A. Nassalski, et al. , “Application of Hamamatsu S8550 APD array to the Common

PET/CT Detector”, IEEE Trans. Nucl. Sci., vol 55, no 5, pp., Oct. 2008.

Thank you www.ipj.gov.pl/anassalski/Files/pliki.html

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