ce doped lanthanum tri-bromide crystal: recent advances in scintillation imaging
DESCRIPTION
Ce doped lanthanum tri-bromide crystal: recent advances in scintillation imaging. Roberto Pani On behalf of SCINTIRAD Collaboration INFN and Sapienza-University of Rome Italy. LaBr 3 :Ce/PMT Pulse height non linearity. Co 60 gamma ray pulse height spectra measured with LaBr 3 :Ce - PowerPoint PPT PresentationTRANSCRIPT
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