CANADA’S NATIONAL LABORATORY FOR PARTICLE AND NUCLEAR PHYSICS
Owned and operated as a joint venture by a consortium of Canadian universities
via a contribution through the National Research Council Canada

MPPC and Liquid Xenon
technologies from particle physics
to medical imaging
Fabrice Retière
TRIUMFLABORATOIRE NATIONAL CANADIEN POUR LA RECHERCHE EN PHYSIQUE NUCLÉAIRE ET EN PHYSIQUE DESPARTICULES
Propriété d’un consortium d’universités canadiennes, géré en co-entreprise à partir d’une contribution
administrée par le Conseil national de recherches Canada

1Outline
T2K FGD

Xenon TPC (TRIUMF not involved)

Monolithic LSO crystal readout for PET

Liquid Xenon
TPC for PET

2

Positron Emission Tomography

3

PET imaging• PET is a functional imaging
technique– Image biological processes– Tracer are design to target
specific processes (e.g.
tumors)• PET does not necessarily
show anatomical feature– The better the tracer the
fewer additional features– Need an additional imaging
technique (MRI, CT)4Blurring in PET• Random combinations– Reduced by timing resolution• Scatter (Compton interactions inpatient)– Reduced by good energy
resolution• Position resolution– Depth of interaction• Need new techniques• Compton interactions in detector– Reduced by higher atomic Z• Statistics!!!
– Image reconstructed by combining
many lines of response5– Time of flight would helpRequirement for PET
Energy resolution• Important for removing
scatters

Photo-electric
absorption– Energy lost in scatters
implies lower energy– 4% FWHM resolution istypically sufficient forremoving all scatters• Randoms are often scatterand are hence also reduced• Energy resolution is criticalfor Compton reconstruction
if multiple interactions areto be reconstructed

Compton edge
(180⁰ scattering)6

A typical micro-PET detector
Siemens Focus 120
Features

Focus 120

Detector diameter

15 cm

Bore size

12 cm

Axial field of view

7.6 cmNumber of detector blocks

96

Number of LSO elements

13,824

LSO element size

1.6x1.6 mm2

Performances

Focus 120

Peak sensitivity>7%

Resolution at center of FOV<1.4mmAverage energy resolution

18%

7

State of the art: clearPEM

1st clinical images with ClearPEM• ClearPEM: State of the art PEM– Very good 3D resolution– High sensitivity– Complex: 12,000 avalanche
photodiodes and associatedelectronics• MPPCs could easily replace APDs

Nucl. Instrum. And meth. Volume 571, Issues 1-2, (2007), Pages 81-84

8

Reducing complexity by opticalmultiplexing• R&D by UC Davis groupusing Wavelength shiftingbars– 2×2×20 mm3 LYSO
crystals– 2×2×20 mm3 WLS bars

H. Du, Y. Yang, and S. Cherry
Phys. Med. Biol. 53 (2008) 1829–1842• Large prototype by AXPET
collaboration– 3×3×100 mm3 LYSO crystals– 0.9×3×40 mm3 WLS bars
– Detector being tested

9

https://twiki.cern.ch/twiki/bin/view/AXIALPET/WebHome

An optical multiplexer:
The Fine Grained Detector

U. British Columbia, Kyoto U., U. Regina, TRIUMF, U. of Victoria• Two detectors– 15 XY layers (192 bars)– 7 XY layers + 7 water
panels• 8448 channels

10T2K Multi-Pixel Photon Counter
Pictures courtesy of Kyoto University• A type of Pixelated
Photon Detector (PPD)
made by Hamamatsu
Photonics• Main features– High gain (106)– 1.3x1.3 mm2 active area
• 667 50 mm pixels– Photon detection
efficiency ~ 30%– Insensitive to magnetic
field– Pixelated: 1 pixel = 1
photon (or multiple
photons)
11

Characterization ofT2K MPPCs• Gain– Including fluctuations• Dark noise• After-pulsing• Cross-talk• Recovery• Saturation

12

MPPC nuisances

13

MPPC recovery and saturation

MPPC

14

Using MPPCs from T2K to PET
Features and drawbacks

T2K

PET

Insensitivity to magnetic field

Yes

Yes, with MRIHigh photon detection efficiency

Yes

Yes

High gain

Yes

Yes (simplify
electronics)

Fast rise time

No

Yes

Saturation

Not a big issue

May affect resolution

Small active area

Not an issue

May be an issue

Dark noise

Small enough

Depend on area

After-pulsing

Small enough?

Cross-talk
Small enough?
MPPC are a good match to small (1x1 to 3x3 mm2) LSO crystals.
New PET detector are being designed with MPPCs, lots of MPPCs…
15

Reading out a monolithic LSO crystal
with WLS bars and MPPCs•

Goals– Position resolution < 2 mm
(FHWM) in every dimension– Energy resolution < 20% (FHWM)– Timing resolution < 3 ns (FWHM)•

Concept

14.4cm– Large LSO crystal: 144×144×20mm3– Light transported to the side by
Wavelength shifting bars or clear
light guides• Dimension: 3×3×150 mm3• 48 bars per side
• 96 channels per module compare to
12,000 for clearPEM!

– Readout by 3×3 mm2 MPPCs

14.4cm16

Using wavelength shifting bar to
reduce the number of channel• 16,500 blue photons are
emitted by a 511 keV
photon in a LSO crystal• Some blue photons areabsorbed in wavelength
shifting bars at the top andbottom– The WLS bar reemitted
green photons– A small fraction of thephotons is trapped in the
bar and travel to the end to
be detected
17

Position reconstruction• Along crystal transverse
directions: “weighted
mean”• Along crystal depth: lightspread– Limited by angle of totalreflection: ~50 degreewith optical gel, ~30
degree with air gap• Keys to good resolution– Light collection > 5%
– Noise < 0.1 photo-electron• Possible with MPPCs
Total internalreflection
LSO

Interaction
pointLight cone
entering the bars

18

Photon collection: key to good
performances
H. Du, Y. Yang, and S. Cherry
Phys. Med. Biol. 52 (2007) 2499–2514

LSO• Photon propagation in
LSO and LSO-WLS
reemission wellunderstood• Main issue is reflection
efficiency along theedges of the fibers• For this concept to workneed > 100 photons– > 97% reflection
effiency

19

MPPCLight collection (simulations)
GEANT simulations
LSO

LSO

20

Position resolution (simulations)
GEANT simulations

LSO

21

Prototype• Building a prototype insummer 2010
• Test in fall 2010
• 6 by 6 WLS bars
– Readout alternatively
on either side
– Need 12 MPPCs• 1.8x1.8x1.2 cm2 LSO
crystal• We will know if thisconcept is sound22

Light spread for different positions
GEANT simulations

If the measured photon collection is as good as
simulated, this concept will work… Answer in 3-4 months

23

From LSO to liquid Xenon
Liquid Xenon is a good scintillator
Parameter

BGO

LSO

LXe

Comment

Attenuation length
at 511 keV

11 mm

12 mm

36 mm

Required depth ≥ 10 cm

Photo-electric
fraction

42%

33%

22%

Require handling
Compton interactions# Photons at 511
keV

3,300

16,40012,000(2kV/cm)

Decay time

300 ns

40 ns

2 ns (97%)
27 ns (2%)

< 1ns timing resolution
possible in principle

Peak wavelength

480 nm

420 nm178 nmRequire special photosensors

And, an excellent ionization detector
24Liquid Xenon for microPET
A breakthrough technology?
• Achieving ultimate performances at low cost?
• Used for physics experiments for example dark
matter search• Key advantage is to combine high Z material
with the ability to detect scintillation light andionization charge at the same time
– Allow the best of both world25

microPET detector concept

APDs

Anode strips and wires

Compton+photo-electric

Photo-electric
Cathodegg

26

Liquid Xenon detector specifications
Features

Focus 120

LiquidXenon

Detector diameter

15 cm

12 cm

Bore size

12 cm

10 cm

Axial field of view

7.6 cm

8 cm

Number of detector blocks

96

12

Number of readout elements

13,824~3,000Element size

1x1x1 mm3

Performances

1.6x1.6x20mm2Focus 120

Liquid Xenon

Peak sensitivity

>7%

>10%

Resolution at center of FOV<1.4mm< 1mm

Average energy resolution

18%

10%
27

Micro-PET concept28

First prototype to investigate energy
resolution• 4% (sigma) has beenmeasured• Build a test chamber toinvestigate energy
resolution– Use APD
– Use Time Projection
Chamber configuration

29

Energy resolution• Before combining
resolution dominatedby recombination
fluctuations• After combination main
source of fluctuations:– Electronic noise onelectrode (ionization)• 2.7%– APD gain fluctuation• 2.7%

30

Second prototype. Full scale detector• Operated from fall 2009
• Few issues– Achieving required
purity has been achallenge– Signal to noise on APD
is border line

31

Such chamber can be used to measurecosmic rays

32

Position resolution from cosmics

1mm (FWHM)

33

Detecting 511 keV photons

34

Two issues with prototype• Purity• Electronics noise– So far purity not goo
enough– Carbon particle fromcarbon loaded kapton
40-70 ms life time
Different running period– Collect 15,000 – 20,000
e- at 511 keV– Requirement, noise ~15 keV• Equivalent noise charge= 600 e• Not so well defined overwhat frequency• Pick up noise can be aserious issue35

Dealing with Compton interactions• The 1st interaction in Xenon is a Compton 78%
of the time
– Distance between the 1st and 2nd interactions
exceed position resolution• Finding the first interaction point is critical toachieve pointing resolution• In addition Compton reconstruction may be
used to reject background36

A large number of configurations
Topology

Intrinsic

2 hit
distance >1 mm

Hit E > 50
keV

both

1-1

7.6%

9.7%

9.7%

12.3%

1-2

20.8%

24.4%

28.0%

31.6%

1-3

12.6%

13.1%

12.5%

12.0%

1-4

4.9%

4.4%

2.2%

1.8%

2-2

14.1%

15.0%

20.2%

20.3%

2-3

17.3%

16.3%

18.1%

15.5%

2-4

6.7%

5.5%

3.2%

2.3%

3-3

5.3%

4.4%

4.0%

2.9%

3-4

4.0%

2.9%

1.4%

0.9%

4-4

0.8%

0.5%

0.1%

0.1%

No need to investigate higher order topological configurations

37

Compton reconstruction algorithm• Build every possible interaction
sequence using the information
on both detector sides– Reject the sequence that lead toLine of Response outside thesample volume• For each sequence
Sequence 1

Sequence 2(rejected by LOR)

Sequence 3

Sequence 4, 5, 6 not shown– Calculate two angles at every
possible scattering point• From energy deposited• From geometry• Assess the errors of both methods(energy always dominate errors)– Calculate a chi2 quantity
comparing the energy andgeometrical angle– Select the sequence with lowestchi238

Algorithm evaluation by simulations• Simulate using GEANT• Use NEMA phantom scaled for
micro-PET• 1-2 and 2-2 have the worst
signal to background– Some irresolvable ambiguities• Most of the background is due
to selecting wrong first point– Random and scatter very much
suppressed due to very goodenergy and time resolution
39

FocusLiquid Xenon promise excellent image
quality

Simulations

40

Summary• PET is continuously evolving– Current trend is towards ever smaller crystals andan ever larger number of channels• TRIUMF is developing alternate solution– Liquid Xenon• Extremely promising technology yet complex– Reading out monolithic LSO crystal withwavelength shifting bars
• Hopefully validate the concept before end of 2010
• Development of GEANT simulations
41

Collaboration• Liquid Xenon collaboration
A. Miceli, P-A. Amaudruz , J.Glister, L. Kurchaninov, F. Retière, T.J. Ruth
(TRIUMF)
F. Benard (BCCA)
D.A. Bryman, C. Clements, A.J. Stoessl, V. Sossi, H. Zhu (UBC)
J-P. Martin (U. Montreal)• Scintillator detectors

C. Lim, F. Retière, P. Gumplinger, C. Ohlman (TRIUMF)

42

CANADA’S NATIONAL LABORATORY FOR PARTICLE AND NUCLEAR PHYSICS
Owned and operated as a joint venture by a consortium of Canadian universities
via a contribution through the National Research Council Canada

BackupLABORATOIRE NATIONAL CANADIEN POUR LA RECHERCHE EN PHYSIQUE NUCLÉAIRE ET EN PHYSIQUE DESPARTICULES
Propriété d’un consortium d’universités canadiennes, géré en co-entreprise à partir d’une contribution
administrée par le Conseil national de recherches Canada

43

Corresponding electrical circuit
Quenchingresistor

RquenchCquenchRquenchCquenchRquenchCquenchRquenchiavalanche

Cpixeliavalanche

Cpixeliavalanche

Cpixeliavalanche

CpixelCline

CquenchParameters for T2K MPPC
Cpixel = 90 fF
Rquench = 150 kW
Cquench ~ 4 fF (parasitic)
Cline ~ 10 pF (parasitic)
Iavalanche = (Voperation – Vbreakdown) / Rquench ~ 5-10 mA
44Q
avalanche = (Voperation – Vbreakdown) Cpixel ~DiodeMPPC signal
Charge distribution of 9 INGRID channels

T. Murase (Tokyo University)
M. Otani (Kyoto). PD09 talk45