labr3:ce scintillation gamma camera prototype for x and

iWoRiD 2-6 July 2006

8th International Workshop on Radiation Imaging Detectors

Pisa 2-6 July 2006

LaBr3:Ce scintillation gamma camera prototype for X and gamma ray imaging

Roberto Pani

On behalf of SCINTIRAD CollaborationINFN University La Sapienza Rome Italy


In 2004, INFN promoted the development of a scintillation camera based on LaBr3:Ce continuous crystal shape.

LaBr3:Ce crystals are now available with continuous shape covering up to 10×10 cm2 with a thickness of 1 cm or more. (the high hygroscopicity and fragility of material have introduced serious concerns in pixellated manufacturing).

AIM of the work• Verify if LaBr3:Ce meets the requirements for SPECT

imaging and has the potential to replace NaI:Tl as the material of choice for SPECT.

• Explore the potential of LaBr3:Ce as integrated detector, with sufficient spatial resolution, for SPET/CT co-registration imaging (scintimammography)


Crystal scintillation properties

Crystals Density(g cm-3)

Light yield(ph/keV)

Decay time(ns)

Maximum Emission

(nm)

∆E/E (FWHM) (%) PMT read-out

662 keV ** 140 keV

NaI:Tl 3.67 41 230 410 5.6 8.5CsI:Na 4.51 40 630 420 7.4 9.5

14

8.0 *5.8

182220

CsI:Tl 4.51 66 800 ÷ 6 x103 550 6.6 (PMT)/ 4.3 (SDD)

LaCl3:Ce 3.79 49 28 350 3.8LaBr3:Ce 5.0 63 16 380 2.8

Bi4Ge3O12 (BGO) 7.1 9 300 480 9.0Lu2SiO5:Ce (LSO) 7.4 26 40 420 7.9Gd2SiO5:Ce (GSO) 6.7 8 60 440 7.8YAl O3:Ce (YAP) 5.5 21 30 350 4.3 APD

** from C.W.E. van Ejjk Phys. Med. Biol. (2002) 85-106 * Expected values


Radiation absorbtion properties

at 140 keV

Crystals ρdensity (g cm-3)

τ (cm-1) µ (cm-1) τ / µ HVL (cm)

Thick.*80% eff. (cm)

LaBr3:Ce 5.0

3.793.674.51

2.2 3.01 0.73 0.23 0.53

LaCl3 :Ce 1.78 2.37 0.75 0.29 0.68NaI:Tl 2.07 2.66 0.78 0.26 0.60CsI:Tl 3.17 3.92 0.81 0.17 0.41


Non-proportionality in light yield

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

1 10 100 1000Energy (keV)

Rel

ativ

e Li

ght Y

ield

LaBr3(Ce)B

NaI(Tl)A

A – Prescott and Narayan, Nucl. Instr. And Meth., Vol 75,51 (1969)B – G.Bizarri, W.E.Van Eijk et al., IEEE TNS, Vol 53,02 (2006)

W.Moses, NIM A, 487 (2002)


LaBr3:Ce Afterglow

Exp. time: 300 s – Source : 241Am

(Nassalski A. et al. IEEE NSS_MIC

Conf. Rec., 2005)

Exp. time: 30 s – Source : X-ray beam

(Bizarri G. et al. IEEE TNS, Vo. 35, 2006)


Energy Resolution

1%

10%

100%

10 100 1000Energy (keV)

Ener

gy re

solu

tion

FW

HM

LaBr:Ce 4mm thick / PMTLaBr:Ce 0.5 inch thick / PMTLaBr:Ce 0.5 inch thick / APDNaI(Tl) Dorenbos TNS 2004Theoretical=2.35/sqrt(Nphe)

0.5” Ø ×0.5” /PMTA

0.5” Ø ×0.5” /APDB

A PMT Hamamatsu R3261 B Si-APD Hamamatsu S8664 - Active Area 10 x 10 mm2


LaBr3:Ce X and γ imager

external size 52 x 52 mm2

49 × 49 mm2 active area

1.5 mm glass window

metal channel dynodes

8×8 matrix 6.0 mm anodes

Hamamatsu H8500

Flat Panel PMT

LaBr3:Ce planar scintillation crystal5 mm thick integralassembled with Flat

Panel PSPMT

LaBr3:Ce planar scintillation crystal10 mm thick + 3 mm window coupled to Flat Panel PSPMT

Photodetector assembly for

10x10 cm2 LaBr3:Ce crystal

Extremely compact(15 mm of thickness)

Ideal for closely packing in array (1.5 mm edge dead zone)Intrinsic spatial resolutionbetter than 0.5 mm


FlatFlat Panel Panel ElectronicElectronic ReadoutReadout: : Multi-anode 64 channels

PCDAQ Board(A/D)

RAL HX2 IntegratingAmplifier

(16 ch)RAL HX2 IntegratingAmplifier

(16 ch)

Anode 1

Anode 2


(16 ch)

Anode 16


(16 ch)

PSPMTH8500

Flat Panelphot

ocat

ode

Anode 48

Anode 64

Comparator

Event TriggerLast

Dynode

Control Logic

Southampton Read64

Multiplexer

NI DAQ 6110E


Position Arithmetic for continuousscintillator in single photon counting

1 2 3 4 5 6 7 8 … i

∑=k

k

ii nn

kin

k12345678

Anode array (Hamamatsu H8500)Charge distribution samplingby anode array

Position:

Energy:

Σi i niΣi ni

X =

Ε = Σi ni

X & Y Position Centroid AlgorithmScintillation light flash on photocathode


Expected Spatial Resolution

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50Position (mm)

Spa

tial R

esol

utio

n (m

m

1 2 3 4 5 6 7 8Anodes

tribcharge_disERSR σ×=

LaBr3(Ce) 1,5 mm

LaBr3(Ce) 10 mm

( ) iii f∑ ><−=i

phe

cX n1σ 2

pheii nnf =

i

in

LaBr3(Ce) 5 mm

Projected charge ( X-axis)


Charge distribution treatment for position linearity correction

Original charge distribution

from single γ interaction

Threshold level

Squared charge

LaBr3:Ce

10 mm thick


Position linearity correction

0

10

20

30

40

50

0 10 20 30 40 50Mechanical Position (mm)

Mea

sure

d Po

sitio

n (m

raw datacharge threshold = 1y=x

Corrected

Raw

The correct position

linearity relation enables

to carry out the true

intrinsic spatial resolution

LaBr3:Ce

integral assembly

Co57 Spot scanning,

1.5 mm stepM

easu

red

Posi

tion

(mm

)

0

550

1100

1650

2200

90 120 150 180 210Image Pixel

Cou

nts

Raw data

Cou

nts

0

500

10001500

2000

2500

90 120 150 180 210image pixel

Cou

nts

(a.u

Threshold & squared charge

Cou

nts


LaBr3:Ce Position Linearity Enhancement continuous crystals

3 inch PSPMT

Hamamatsu R2486

10 mm thick + 3 mm window

Sanchez F. et al., “Design and tests of a portable mini gamma camera”, Med.Phys. , Vol.31,June 2004


LaBr3:Ce Energy and Spatial Resolution Enhancement

Sanchez F. et al., Medical Physics, Vol.31, June 2004

3 inch PSPMT Hamamatsu R2486

continuous crystals


Intrinsic Spatial Resolution vs Energy

0.1

1.0

10.0

10 100 1000Energy (keV)

Intri

nsic

SR

(mm

)

E1

∝

0.5 mm @ 511keV

Anger Camera 10 mm

LaBr3(Ce) 10 mm

LaBr3(Ce) 5 mm

LaBr3(Ce) 1.5 mm

broken line


Intrinsic Spatial Resolution vs γ energyLaBr3:Ce 5 mm thickness- 1mm collimated Ba133 source

0

200

400

600

800

70 110 150 190 230

image pixels

coun

ts

80 keV

ISRavg=1,14mmISRmin=0,83mm

5mm

Overall SR = 1.51 mm

0

20

40

60

80

100

120

70 120 170 220image pixels

coun

ts

302 keV

ISRavg=0,73mmISRmin=0,48mm

5mm

Overall SR = 1.24 mm


Spatial resolution vs crystal thicknessCo57 1 mm collimated source - Detector Scanning @ 1.5 mm step

0

550

1100

1650

2200

70 90 110 130 150 170 190Image Pixel

Cou

nts

Intrinsic SR = 1.00 mm mean value

0.90 mm best value

LaBr3:Ce 5 mm thick

Integral assembly

0

400

800

1200

1600

70 90 110 130 150 170 190Image Pixel

Cou

nts

Intrinsic SR = 2.05 mm mean value

1.85 mm best value

LaBr3:Ce 10 mm thick

3 mm window


Absorption efficiency of BrilLianCe TM 380

(LaBr3:Ce)

Courtesy of Saint Gobain Crystals

80 keV

140 keV

511 keV


4.6mm

1.2mm

LaBr3:Ce 5 mm thickness -Integral assembly

Spatial Resolution = 0.90 mm – Efficiency: 80%

LaBr3:Ce 1.5 mm thickness -Integral assembly

Spatial Resolution = 0.65 mm – Efficiency: 35%

(S. Majewsky, Jlab, Va, USA)

“Mario” transmission Pb mask

Co57 flood field irradiation


Conclusion

• This work confirms the expected high potential of the LaBr3:Ce gamma camera for single photon Imaging.

• Continuous LaBr3:Ce crystal shows superior spatial and energy resolution performances than previous generation scintillators

• It shows interesting features as integrated detector for SPET/CT imaging though the wide charge distribution detection in pulse mode is the major limitation for high count rate X-ray imaging

labr3:ce scintillation gamma camera prototype for x and

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