ce doped lanthanum tri-bromide crystal: recent advances in scintillation imaging

Ce doped lanthanum tri-bromide crystal: recent advances in

scintillation imaging

Roberto Pani

On behalf of SCINTIRAD CollaborationINFN and Sapienza-University of Rome Italy

LaBr3:Ce/PMT Pulse height non linearity

Gamma Ray Spectroscopy With a Ø 19 x19 mm3 LaBr3 : 0:5% Ce3+ ScintillatorP. Dorenbos, J. T. M. de Haas, and C. W. E. van Eijk, Member, IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 51, NO. 3, JUNE 2004

Co60 gamma ray pulse height spectra measured with LaBr3:Ceat cathode voltages a) HV = -500 V and b) HV = -700 V.

Scintillation crystals

• Planar LaBr3:Ce 49494 mm3 + 3 mm glass window

• Planar NaI(Tl) 49494 mm3 + 3 mm glass window

• LaBr3:Ce cylinder ½” Ø ½” thickness (gold standard)

R6231 Hamamatsu:optimized PMT for LaBr3:Ce crystal

• QE typ. = 30 % @ 420 nm

• Number of dinode = 8

• Gain= 2.7 E+05 @ HV= -1000 V

• Voltage Divider modified by Saint Gobain

Pulse height linearity vs photon energy

0

400

800

1200

1600

2000

0 200 400 600Energy (keV)

Ch

an

ne

l

planar LaBr

best fit LaBr

cylinder LaBr

best fit cyl. LaBr

HamamatsuR6231

HV=-1000V

Energy resolution FWHM R6231 Hamamatsu PMT @ HV=-1000 V

Planar LaBr3:Ce 49x 49 x 4 mm3 + 3 mm windowPlanar NaI(Tl) 49x 49 x 4 mm3 + 3 mm windowCylinder LaBr3:Ce ½” Ø x ½ “ thickness

Overall Energy Resolution: Theory

1

56.522

NRER s

•Rs= intrinsic resolution of scintillator crystal•N = mean value of photon= 0.3 , =0.98, ~4.8 (PMT R6231 Hamamatsu @ HV=-1000 V)•Photon Energy 122 keV

Crystal Intrinsic

Energy

Resolution

@122 keVa

Energy

Resolution

(theor.)

Energy

Resolution

(exp.)

Nphe

(theor.)

Nphe

(exp.)

LaBr3:Ce

Planar

4.6% 7.1 %(70000 ph/MeV)

6.9% 2475 2478

NaI(Tl)

Planar

6.6% 9.55%(38000 ph/MeV)

9.50% 1344 1369

a:Comparative study of scintillators for PET/CT detectorsNassalski, A.; Kapusta, M.; Batsch, T.; Wolski, D.; Mockel, D.; Enghardt, W.; Moszynski, M.;Nuclear Science Symposium Conference Record, 2005 IEEE, Volume 5,  23-29 Oct. 2005 Page(s):2823 – 2829

LaBr3:Ce - Energy Resolution Summary

Energy (keV)

Hamamatsu R6231 +

Planar LaBr

(49x49x4 mm3) (2006)

Hamamatsu

R6231 +

LaBr Cylinder

(1/2”Øx1/2”thick) b

(2005)

Photonis XP20Y0QDA +

LaBr

(10x10x5 mm3)a

(2004)

60 9.8% 10.6% 13.0%

81 8.6% 9.3% 10.0%

122 6.8% 6.9% 8.0%

356 4.0% 4.3% -

511 3.3% 3.1% 4.0%a:Comparative study of scintillators for PET/CT detectorsNassalski, A.; Kapusta, M.; Batsch, T.; Wolski, D.; Mockel, D.; Enghardt, W.; Moszynski, M.;Nuclear Science Symposium Conference Record, 2005 IEEE, Volume 5,  23-29 Oct. 2005 Page(s):2823 – 2829

bX-ray and gamma-ray response of a 2”x2” LaBr3:Ce scintillation detector F. Quarati, A.J.J. Bos, S. Brandenburg, C. Dathy, P. Dorenbos, S. Kraft,R.W. Ostendorf, V. Ouspenski, Alan Owens, Nuclear Instruments and Methods in Physics Research A 574 (2007) 115–120

H8500 Hamamatsu FP :

• Metal channel dynode

• QE typ. = 24 % @ 420 nm

• Number of dinode = 12

• Gain= 1.5 E+06 typ.

• Number of anodes = 8 x 8 array

(6.08 mm pitch)

Energy resolution analysis The output signal was obtained from the

short circuit of all anodic signals

15 mm 50 mm

Pulse height linearity vs photon energy

LaBr3:Cecontinuous crystal

+ HamamatsuH8500 FP(sc anode) HV=-1000V

0

500

1000

1500

2000

0 100 200 300 400 500 600Energy (keV)

Cha

nnel

-25%-20%-15%-10%

-5%0%5%

10%

0 100 200 300 400 500 600

Energy (keV)

De

via

tion

%

Energy resolution H8500 Hamamatsu F.P. (sc anode) @ HV= -1000V

Planar LaBr3:Ce 49 x 49 x 4 mm3 + 3 mm glass window

QE max. = 41.6 % @ 380 nm Number of dinode = 10 Gain= 2.0 E+06 @ HV=-800 V

R7600-200 Hamamatsu PMT

LaBr3:Ce Cylinder (½”Ø ½” thickness)

1%

10%

100%

10 100 1000

Energy (keV)

R7600-200 (QE = 41%)

R6231 standard PMT (QE = 30%)

H8500 MA-PMT (QE = 22%)

1%

10%

100%

10 100 1000

Ene

rgy

Res

olut

ion

R7600-200 Hamamatsu LaBr3:Ce Cylinder (½” Ø x ½ “ thickness)

Ba133 source HV=-700V

0

100

200

300

400

500

0 500 1000 1500 2000 2500 3000

channel

Co

un

ts

32 keV81 keV

274 keV302 keV

356 keV

380 keV

0

500

1000

1500

2000

0 200 400 600 800 1000 1200 1400

channel

coun

ts

274/302 keV356/380 keV

NaI(Tl) planar + R6231

Scintillation

event

PSF Image

Light PSF

phe

PSF

imm

n

0

10

20

30

40

50

0 10 20 30 40 50mechanical position (mm)

mea

sure

d po

sitio

n (m

m)

0

1250

2500

3750

5000

0 100 200 300

Pulse height (a.u.)

coun

ts (

a.u.

)

phenE

1R

Co57 pulse height analisys

PSF image

Position linearity

lPSFSR immSpatial Resolution

mech

channel

dx

dXl

Centroid Algorithm for small FoV gamma camera

jj

jjj

c n

xn

X'

'

k

kjj tnn

2'

jj

jjj

cn

xn

X

Standard algorithm:

k

kjj nn

New algorithm:

1 2 3 4 5 6 7 8

S1

S3

S5

S7

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8

S1

S3

S5

S7

0

5

10

15

20

25

30

35

40

After procedure

t = threshold (0÷1)

LaBr3:CeCharge spread

HV=-825V

Performances Analysis:

LaBr3(Ce)49 49 4 mm3 + 3 mm glass window

• Coupled to the MA-PMT H8500 tube

• 0.4 mm Øcollimated Tc99m source (140 keV photon energy) 1.5 mm step scanning

• Image analysis with and without new

algorithm

LaBr3(Ce): Overall Spatial Resolution@140 keV

SR = 1.67 mm

SR = 1.90 mm

HV=-800V

0

100

200

300

400

500

600

150 200 250 300 350 400

image pixel

co

un

ts

HV=-750V

0

100

200

300

400

500

600

700

150 200 250 300 350 400

image pixel

coun

ts

HV=-750V

0

100

200

300

400

500

600

150 200 250 300 350 400

image pixel

counts

SR=1.36 mm

SR=1.28 mm

HV=-800V

0

100

200

300

400

500

600

150 200 250 300 350 400

image pixel

co

un

ts

HV = - 800V

HV = - 750V

Standard algorithm New algorithm

0

0.2

0.40.6

0.8

1

1.2

0 20 40Mechanical Position (mm)

Pu

lse

He

igh

t Ce

ntr

oid

(%

)

LaBr3(Ce)

MC simulation

Experimental data vs Monte Carlo simulation GEANT4:

Pulse Height Centroid @ 140 keV

0

2

4

6

8

10

12

14

-30 -20 -10 0 10 20 30Mechanical Position (mm)

Sp

rea

d (S

igm

a -m

m)

MC Simul.LaBr HV=-775V

1 23

45

67

8

S1

S2

S3

S4

S5S6

S7S8

0.00

0.50

1.00

1.50

2.00

2.50

3.00

1 2 3 4 5 67

8

S1

S2

S3

S4S5

S6S7

S8

0

20

40

60

80

100

120

Experimental data vs Monte Carlo simulation: Charge distribution spread @ 140 keV

Monte Carlo Simulation

LaBr3:Ce49x49x4 mm3

continuous crystal + H8500 MA-PMT

Experimental measurement:•0.4 mm Ø point source Tc99m

•1.5 mm step

Monte Carlo simulation:•140 keV photon energy•6 mm step

LaBr3:Ce49x49x4 mm3 + 3mm glass window

continuous crystal +

8x8 anode array

Experimental data vs Monte Carlo simulation:

Spatial resolution & position linearity without new centroid algorithm

0

50

100

150

200

250

300

-30 -20 -10 0 10 20 30

Mechanical position (mm)

Ima

ge

Po

sitio

n (

pix

el) Experimental data

Monte Carlo data

Theoretical linearity

Experimental data vs Monte Carlo simulation:

Spatial resolution & position linearity with new centroid algorithm

00,20,40,60,8

11,21,41,61,8

2

0 10 20 30 40 50

Mechanical position (mm)

Sp

atia

l res

olu

tio

n (

mm

)

Monte Carlo Data

Experimental data

Experimental measurement:•0.4 mm Ø point source Tc99m

•1.5 mm step

Monte Carlo simulation:•140 keV photon energy•6 mm step

LaBr3:Ce49x49x4 mm3 + 3mm glass window

continuous crystal +

8x8 anode array

Conclusions

• LaBr3:Ce seems a very attractive scintillation crystal for SPET application (140 keV)

• At 140 keV photon energy, continuous crystal can allow the highest values of spatial resolution, energy resolution and detection efficiency

• Hamamatsu MAPMT photodetector are limiting energy resolution and spatial resolution response

• Probably the new ultra high Q.E. MAPMT could solve such limitations