iWoRiD 2-6 July 2006 8th International Workshop on Radiation Imaging Detectors Pisa 2-6 July 2006 LaBr 3 :Ce scintillation gamma camera prototype for X and gamma ray imaging Roberto Pani On behalf of SCINTIRAD Collaboration INFN University La Sapienza Rome Italy
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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
iWoRiD 2-6 July 2006
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)
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
iWoRiD 2-6 July 2006
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)
iWoRiD 2-6 July 2006
Charge distribution treatment for position linearity correction
Original charge distribution
from single γ interaction
Threshold level
Squared charge
LaBr3:Ce
10 mm thick
iWoRiD 2-6 July 2006
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
iWoRiD 2-6 July 2006
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
iWoRiD 2-6 July 2006
LaBr3:Ce Energy and Spatial Resolution Enhancement
Sanchez F. et al., Medical Physics, Vol.31, June 2004
3 inch PSPMT Hamamatsu R2486
continuous crystals
iWoRiD 2-6 July 2006
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
iWoRiD 2-6 July 2006
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
iWoRiD 2-6 July 2006
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
iWoRiD 2-6 July 2006
Absorption efficiency of BrilLianCe TM 380
(LaBr3:Ce)
Courtesy of Saint Gobain Crystals
80 keV
140 keV
511 keV
iWoRiD 2-6 July 2006
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
iWoRiD 2-6 July 2006
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