A novel gamma-ray detector with sub-millimeter resolutions using a monolithic MPPC array with pixelized Ce:LYSO and Ce:GGAG scintillators Takuya Kato J.Kataoka, T.Nakamori, T.Miura, H.Matsuda A.Kishimoto (Waseda Univ.) K.Sato, Y.Ishikawa, K.Yamamura, S,Nakamura N.Kawabata (Hamamatsu) H.Ikeda (ISAS/JAXA) S.Yamamoto (KCCT) K.Kamada (Furukawa Co., Ltd.) 8 December th Hiroshima Academia Sinica, Taipei

Contents 2 1.PET and our approach 2.Performances of the MPPC array 3.Charge division readout technique 4.Sub-millimeter pixelized scintillators 5.Future prospects and summary

Positron Emission Tomography 3 ⇒ Well-established method for detecting cancers PMT is incorporated in conventional PET scanner However, PMT is … PMT Scintillator intricate in construction large size sensitive to B fields APD can overcome these points Functional imaging with 511keV annihilation gamma-ray Time of Flight(ToF) and Depth of Interaction(DoI) information improve image quality ToF DoI MRI-PET has become common as a multimodality imaging device ⇒ compactness, low power and ⇒ insensitivity to B fields is required high time resolution are required Cancer

APD-PET project 4 Kataoka, Matsuda et al. 2009, NIM-A, 2010 IEEE-TNS Koizumi et al. 2009, Yoshino et al. 2011, NIM -A 256ch APD-array APD is a compact and insensitive to B fields Developed large size APD and dedicated LSI Sub-millimeter resolution was achived Time resolution is a few ns 3.1ns (FWHM) ⇒ unfavorable for ToF APD gain is relatively low (~50) ⇒ easily affected by electric noise contamination

Multi-Pixel Photon Counter 5 2D-array of Geiger mode APD pixels charges proportional to the number of fired pixels compact low bias voltage (<100V) high gain (10 5 ~10 6 ) insensitive to B fields quenching resistor Geiger-mode APD Geiger -mode quenching discharge charge V I V op V br ON Off ~50ns

Characteristics summary 6 High gain, doesn’t need CSA Less photon-detection efficiency Narrow dynamic range due to limited number of pixels ⇒ much better S/N ⇒ much better time resolution (suitable for ToF-PET) ⇒ worse energy resolution ⇒ need linearity correction PMT APD MPPCPD gain Q.E. (PDE) volume interfered by B structure power consumption 10 5~6 >25 large yes complex high ~6 >80>25 small no simple low suitable for PET

4 × 4 Monolithic MPPC array 7  4×4 array with 3×3mm 2 pixel  50μm type (3600 APDs/pixel)  0.2mm gap  With FPC(flexible printed circuit)  monolithic  buttable  low dark counts rate 20deg) 13.6mm Gain vs Voltage Gain 20deg ±5.6% averaged gain = 7.5 × 10 5 Bias Voltage [V] Gain (×10 5 )

Performance with Ce:LYSO 8  4×4 array of 3×3×10mm 3 crystals  reflective BaSO 4 layer divide pixels  coupled using optical grease  irradiated by V 137 Cs spectra energy resolution map 11.5±0.5% (FWHM) ρ =7.10 g/cm 3 25 ph/keV τ =40 ns LYSO array for 662keV Energy [keV] Counts

Time resolution of the MPPC array 9 CFD TAC delay start stop PHADC  PMT  3×3×10mm 3 Ce:LYSO crystal reference detector LYSO PMT MPPC array 22 Na 493±22ps (FWHM) time resolution map

Charge division readout technique 10 resistor network Fan I/O 100ns delay CSADC ×10 linear amp Gate Generator gate (700ns) Discriminator 4ch analog sum ×16ch  often used for MAPMT  16 anodes are connected to red circles  interaction positions are calculated by centroid method  irradiated by V 137 Cs

Result of charge division readout 11 flood image X position (a.u.) Y position (a.u.) 137 Cs spectra  4×4 pixels are clearly resolved  averaged FWHM of peaks is 0.19mm  spectra are extracted from flood image  energy resolution is slightly better 10.2±0.4% (FWHM) for 662keV averaged FWHM of peaks Energy [keV] Counts

Sub-millimeter pixelized scintillator 12 12×12 array 1.0×1.0×10mm 3 17×17 array 0.7×0.7×10mm 3 22×22 array 0.5×0.5×10mm 3 Ce:LYSOCe:GGAG  Ce:GGAG is a brand-new scintillator which has very large light yield  0.1mm thick BaSO 4 layer  coupled with 1mm thick acrylic light guide  read out by resistor network ρ =6.63 g/cm 3 42 ph/keV τ =52.8 resistor network scintillator light guide MPPC array

Comparison between LYSO and GGAG 13 GGAG has larger light yield Decay time of LYSO is shorter ⇒ LYSO is suitable for ToF ⇒ GGAG has better energy resolution  3×3mm 2, 50μm type MPPC  3×3×10mm 3 scintillator crystals 7.9% (FWHM) 9.7% (FWHM) 137 Cs spectra Charge[pC] Normalized counts 3mm GGAGLYSO pulse shapes of 662keV photoelectric absorption events

1.0mm 2 Ce:LYSO array 14 flood image X position (a.u.) Y position (a.u.) 137 Cs spectra  irradiate by 137 Cs  side pixels are overlapped, but central 8×8 pixels are successfully resolved  energy spectra are extracted from flood image 11.5±0.9% (FWHM) for 662keV Energy [keV] Counts

0.7 and 0.5mm 2 arrays 15 flood images 0.7mm 2 Ce:LYSO 0.5mm 2 Ce:LYSO Ce:GGAG 0.5mm 2 Ce:GGAG 11.7±0.7% (FWHM) for 662keV 14.3±1.8% 12.0±1.3% X position (a.u.) Y position (a.u.)  irradiated by 137 Cs  side pixels are overlapped, but central pixels are successfully resolved  energy resolution of GGAG is better than that of LYSO

16 Future prospects Yamamoto et.a ｌ. 2011, IEEE tweezers type coincidence imaging system Monolithic MPPC array with FPC cable Sub-millimeter pixelized scintillator ⇒ more compact ⇒ much better spatial resolution 22 Na Experimental coincidence measurements are conducted Simple 2-dimensional geometrical reconstruction is achieved ~1.3mm (FWHM) ⇒ ~1.3mm (FWHM) resolution

17 Summary MPPC with sub-millimeter scintillator could be promising for high spatial and time resolution gamma-ray imaging, particularly in PET scanner We developed 4×4 monolithic MPPC array Fine gain uniformity of ±5.6% and low dark count rates of ~400kcps were obtained We achieved resolving 0.5mm 2 pixelized scintillator in flood image Energy resolution was 10.2% Time resolution was 493ps (FWHM)

Appendix

About Ce:GGAG Kamada et al. 2011, Cryst Growth Des. Comparison with APD GGAG decay curve decay time 52.8ns (73%), 282ns (27%)

Performances of Hamamatsu MPPC Low dark count (e.g. 3x3mm2, 50um pixel) 10Mcps (2007) --> 5Mcps (2009) --> 1Mcps (2010 – best run) --> consolidate High time resolution (jitter) (e.g. 1x1mm, 1 p.e. level) aro 250ps (2009) --> Lower than 130ps (2010)

Linearity correction 1275keV of 22 Na 662keV of 137 Cs 511keV of 22 Na 356keV of 133 Ba 122keV of 57 Co

Comparison between MPPC and APD Time resolutons MPPC: 624ps(FWHM) APD: 5300ps(FWHM) CFD 100ns delay TAC MCA 22 Na CSA only when using APDs MPPC or APD

Time resolution of APD 155 ps (FWHM) for 10keV beam (=corresponding to the charge of 511keV when coupled with LYSO) CSA limits time resolution Kataoka et al. 2010, IEEE X-ray beam 1-2 ns width TAC

Setup for measuring gain MPP C array LED aluminum case Clock Generato r 100s delay Atten uator Gate Generator Fan I/O CSADC ×100 linear amp gate (100ns ) 465nm CSADC channel Counts LED light spectrum Q offset 1photon 2photon 3photo n

Dark count rates 0.5p.e. level

Gain vs time resolution

Detail about resistor network out1 out4 out3 out2 red ： 51Ω blue ： 100Ω … HV

Charges of 662keV photopeak 3mm 2 1mm 2 0.5mm 2 A D A D 0.7mm A D