A novel gamma-ray detector with sub-millimeter resolutions using a monolithic MPPC array with pixelized Ce:LYSO and Ce:GGAG scintillators

Takuya KatoJ.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 2011 8th Hiroshima Symposium @ Academia Sinica, Taipei

Contents2

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 scannerHowever, PMT is …

PMT

Scintillator

intricate in constructionlarge sizesensitive to B fields

APD can overcome these points

Functional imaging with 511keV annihilation gamma-rayTime 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-TNSKoizumi et al. 2009, Yoshino et al. 2011, NIM -A

256ch APD-array

APD is a compact and insensitive to B fieldsDeveloped large size APD and dedicated LSISub-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 Counter5

2D-array of Geiger mode APD pixelscharges proportional to the number of fired pixelscompactlow bias voltage (<100V)high gain (105~106)insensitive to B fields

quenching resistor

Geiger-mode APD

Geiger-mode

quenching

discharge

chargeV

I

VopVbr

ON

Off ~50ns

Characteristics summary6

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

105~6

>25

large

yes

complex

high

1 50-100 105~6

>80 >25

small

no

simple

low

suitable for PET

4 × 4 Monolithic MPPC array7

4×4 array with 3×3mm2 pixel 50μm type (3600 APDs/pixel) 0.2mm gap With FPC(flexible printed circuit) monolithic buttable low dark counts rate (400kcps @ 20deg)

13.6mm

13.6mm

Gain vs Voltage Gain map @72.01V, 20deg

±5.6%

averaged gain = 7.5 × 105

Bias Voltage [V]

Gai

n (×

105 )

71.5 72.53.5

10

Performance with Ce:LYSO8

4×4 array of 3×3×10mm3 crystals reflective BaSO4 layer divide pixels coupled using optical grease irradiated by 137Cs @20deg, 72.01V

137Cs spectraenergy resolution map

11.5±0.5% (FWHM)

ρ=7.10 g/cm3

25 ph/keVτ=40 ns

LYSO array

for 662keVEnergy [keV]

Cou

nts

Time resolution of the MPPC array9

CFD

CFDTAC

delay

start

stop

PHADC

PMT 3×3×10mm3 Ce:LYSO crystal

reference detector

LYSO

LYSO

PMT

MPPC array

22Na

493±22ps (FWHM)

time resolution map

Charge division readout technique10

1004321

)42()31(

AAAA

AAAAY

1004321

)43()21(

AAAA

AAAAX

resistor network FanI/O

100nsdelay CSADC

×10 linear amp

GateGenerator

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 137Cs @20deg, 72.01V

137Cs

Result of charge division readout11

flood image

X position (a.u.)

Y p

ositi

on (

a.u.

)137Cs 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]

Cou

nts

Sub-millimeter pixelized scintillator12

12×12 array1.0×1.0×10mm3

17×17 array0.7×0.7×10mm3

22×22 array0.5×0.5×10mm3

Ce:LYSO Ce:GGAG

Ce:GGAG is a brand-new scintillator which has very large light yield 0.1mm thick BaSO4 layer coupled with 1mm thick acrylic light guide read out by resistor network

ρ=6.63 g/cm3

42 ph/keVτ=52.8

resistor network

scintillator

light guide

MPPC array

Comparison between LYSO and GGAG13

GGAG has larger light yield

Decay time of LYSO is shorter⇒ LYSO is suitable for ToF

⇒ GGAG has better energy resolution

3×3mm2 , 50μm type MPPC 3×3×10mm3 scintillator crystals

7.9% (FWHM)

9.7% (FWHM)

137Cs spectra

Charge[pC]

Nor

mal

ized

cou

nts

3mm

3mm

GGAGLYSO

pulse shapes of 662keV photoelectric absorption events

1.0mm2 Ce:LYSO array14

flood image

X position (a.u.)

Y p

ositi

on (

a.u.

)137Cs spectra

irradiate by 137Cs 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]C

ount

s

0.7 and 0.5mm2 arrays15

flood images

0.7mm2 Ce:LYSO 0.5mm2 Ce:LYSO 0.5mm2 Ce:GGAGCe:GGAG

11.7±0.7%

(FWHM) for 662keV

14.3±1.8% 12.0±1.3%

X position (a.u.) X position (a.u.) X position (a.u.)

Y p

ositi

on (

a.u.

)

Y p

ositi

on (

a.u.

)

Y p

ositi

on (

a.u.

)

irradiated by 137Cs 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

22Na

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 0.5mm2 pixelized scintillator in flood image

Energy resolution was 10.2% (FWHM @662keV)

Time resolution was 493ps (FWHM)

Appendix

About Ce:GGAGKamada et al. 2011, Cryst Growth Des.

Comparison with APD GGAG decay curve

decay time52.8ns (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

)}/][exp(1{][ akeVbEachADC

1275keV of 22Na

662keV of 137Cs

511keV of 22Na

356keV of 133Ba

122keV of 57Co

Comparison between MPPC and APD

Time resolutonsMPPC: 624ps(FWHM) APD: 5300ps(FWHM)

CFD

CFD100nsdelay

TAC

MCA

22NaCSA

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, IEEEX-ray beam1-2 ns width

TAC

Setup for measuring gain

MPPC array

LED

aluminum case

ClockGenera

tor

100sdela

y

Attenuat

or

GateGenerato

r

Fan

I/O

CSADC

×100 linear amp

gate(100n

s)

465nm

CSADC channel

Counts

LED light spectrum

Q

offset

1photon

2photon3photo

n

100// eQgain

Dark count rates~400kcps @ 0.5p.e. level

Gain vs time resolution

Detail about resistor network

k1 k1

k1k1

nF100 nF100

nF100 nF100

out1

out4

out3

out2

red ： 51Ωblue ： 100Ω

…k10

k10F1

F1

HV

Charges of 662keV photopeak3mm2

1mm2

0.5mm2

A D

1

4

1

4A D

pC9.259.421 pC5.445.410

pC9.249.392

0.7mm2

1

4A D

pC5.445.410