Download - Photodetector requirements for gamma ray imaging with scintillation crystals Roberto Pani
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Photodetector requirements for gamma ray imaging with
scintillation crystalsRoberto Pani
INFN and Sapienza-University of Rome Italy
1th Workshop on “Photo Detection”
June 13 - 14 , 2007 Perugia, Italy
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Individual Coupling
LightSharing
Pixellatedcrystal
Continuouscrystal
Scintillation crystal readout technique
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Individual coupling technique
Munich APD PET*
4 x 8 APD Array (Hamamatsu Photonics)2 x 2 x 6 mm3 LSO individual coupledIntrinsic FWHM ~ 1.2 mm
* Courtesy of Roger Lecomte – Université de Sherbrooke (Québec, Canada)
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Individual coupling technique High packing fraction > 80%
Spatial resolution limited by crystal pixel size ( 1mm tomography, > 1mm planar image) Electronic readout up to 20000 chains (SPET)
Single photoelectron readout not needed
Low noise to allow 140 keV photon energy detection
High gain (104 or more) not needed
Energy resolution depending on scintillation crystal / photodetector
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Light sharing technique
1 2 3 4 5 6 7 8 … i
k
k
ii nn
kin1
2345678
Anode array (Hamamatsu H8500)Charge distribution sampling by anode array
Position:
Energy:
i i ni
i ni X =
i ni
X & Y Position Centroid AlgorithmScintillation light flash on photocathode
k
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
phe
lightPSFim n
phenER 1
0
1250
2500
3750
5000
0 100 200 300
Pulse height (a.u.)
coun
ts (a
.u.)
Co57 pulse height analisys
0
10
20
30
40
50
0 10 20 30 40 50mechanical position (mm)
mea
sure
d po
sitio
n (m
m)
Position linearity
dxdX
l
Image PSF 1mm FWHM
Many γ-ray interactions
one γ-ray interaction
Scintillation light PSF 15 mm FWHM
lSR image
Position determination in light sharing technique
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Light sharing technique
Spatial resolution limited by crystal pixel size ( scintillation array)
Spatial resolution not limited for continuous crystal
Low number of electronic chains
Single photoelectron readout needed
Energy resolution depending on scintillation crystal /photodetector
High gain ( >104 ) is needed
Timing/rise time < 500 ps for ToF
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Point Spread Function and critical angle c
oc n
nsen 52)(0
21
Pixellated crystal / PMT glass window
Light output angle < 45°
Planar crystal / PMT glass window
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Pixellated scintillation crystal
NaI:Tl1m m x 1mm x 4 mm
+H8500 MAPMT
0
400
800
0 500 1000 1500channel
Cou
nts
0
10
20
30
40
50
0 100 200 300 400 500 600
image pixel
coun
ts
Pixel Spatial resolution < 1.3 mm Poor energy resolution ~ 14%Image Spatial resolution > 1.3 mm
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Continuous scintillator crystal1.5 mm step scannig – 0.4 mm Ø Tc99m point source
LaBr3:Ce49 mm x 49 mm x 4 mm+ 3 mm glass window
H8500 MAPMT
0
50
100
150
200
250
300
350
400
450
500
0 5 10 15 20 25 30 35 40 45 50
Mechanical Position (mm)
Imag
e Po
sitio
n (c
hn)
0
100
200
300
400
500
600
700
50 100 150 200 250 300 350 400 450 500
Best Values:
Energy resolution = 9.6 % (@ 1000V) Overall Spatial Resolution= 1.1 mm Intrinsic Spatial Resolution= 1.0 mm
Very good linearity !!!
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
0
0.25
0.5
0.75
1
0 0.2 0.4 0.6 0.8Spatial Frequencies (mm-1)
MTF
(nor
m)
MC simulation LEGPLaBr3(Ce) continuous crystalNaI(Tl) 1,1 mm pixel array
MTF for Continuous CrystalSpatial Resolution limited to LEGPEnhancement in Contrast - increased AUC (Area Under Curve) NO restrictions in image digitization (Nyquist frequency not limited from image pixel)Continuous position responseIncreased detection efficiency
Detector assembly:MAPMT Hamamatsu H8500LEGP collimator (1.5 mm hole, 22 cm lenght)Multi-anode read-out
dxexLSFfMTF fxi2
Crystal samples:LaBr3:Ce continuous, 5mm thickNaI:Tl array, 1.1mm pixel 1.3 pitch
Modulation Transfer Function
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Scintillation crystal: requirements for SPECT (@140 keV)
Z 40 → Photofraction greater than 70%
High density (> 3 gr/cc) → Reduction of crystal thickness to obtain 80-90% efficiency ( important for light collection) Refraction index close to 1.5 → To avoid light loosing due to critical angle (continuous crystal) Decay time 1 s→ To obtain 200 kHz max.
High luminous efficiency (> 20000 at suitable wavelength) → To improve: Decoding crystal pixel in scintillation array
Spatial resolution, in continuous crystal Energy resolution.
Low afterglow for high counting rate
There are few predictions if energy resolution or light output dominates the intrinsic spatial resolution in light sharing
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Density
(g/cm3)
Atten.len. @
140keV*(mm)
Z eff.
Photo-fraction
(%)
Light yield(ph/MeV)
Decay time (ns)
Refr.index
ΔE/E(@140keV
)(PMT)
Emiss max(nm)
NaI:Tl 3.67 3.76 51.0 84 41,000 230 1.85 9% 410
CsI(Tl) 4.51 2.55 52.0 86 66,000 630 1.80 14% 565
YAP 5.50 10.00 36.0 50 21,000 27 1.95 20% 350
LaCl3:Ce 3.86 4.22 49.5 80 40,00027
(65%)1.90 8% 350
LaBr3:Ce 5.07 3.32 47.4 79 63,000 16 (97%) 1.90 6% 380
LuI3:Ce 5.60 1.70 - 90 90,000 30 - -472535
Scintillator crystals for SPECT
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Scintillation crystal: requirements for PET (@ 511 keV)
Z 50 → Photofraction greater than 30%
High density ( >7 gr/cc) → To obtain, in 30 mm crystal length, 50% coincidence efficiency and reduction parallax error for small animal imaging. Scintillation decay time 300 ns → To allow good coincidence time resolution. Time resolution better than 0.5 ns can reduce random coincidences (50 % in a 3D PET) and time of flight can be realized.High luminous efficiency > 8000 ph/MeV →
To enable block detectors with a greater number of pixel (from 8 8 BGO to 16 16 LaBr3(Ce) crystal pixel/module).
Improvement in energy resolution reduces scatter background (25% Compton scattering / 25% “true” events in a 3D PET).
Low afterglow for high counting rate
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Density
(g/cm3)
Emiss. max(nm)
Z eff.Photo-
fraction (%)
Light yield(ph/MeV)
Decay time (ns)
Relative coinc.
efficiency
Coinc. timing res.
(ps)
ΔE/E @511
keV(PMT)
BGO 7.1 480 83 43 9,000 300 100% 3000 10%
Lu2SiO5:Ce
(LSO)7.4 420 65 34 26,000 40 90% 300 10%
Lu2(1-x)Y2xSiO5:Ce
(LYSO)7.1 420 54 - 30,000 40 - - 11%
LaCl3:Ce 3.86 350 49.5 15 46,000 20 (65%) 36% 265 4%
LaBr3:Ce 5.07 380 47.4 14 63,000 16 (97%) 42% 260 3%
LuI3:Ce 5.60472535
- 29 90,000 30 73% 200 <15%
Scintillator crystals for PET
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
2
2. )(355.2)(
MNENC
NR
EE
ERphph
sciee
Intrinsic Scintillation Contribute Non homogeneities Non proportionality of scintillation response
Statistical generation of the signalNph: number of photons in a scintillation flash worsening of the Poisson behaviour Quantum Efficiency
Electronic noisePhotodetector and preamplifier system
[Equivalent noise charge – E. Gatti, NIM Phys Res 1990 ]
PMT P-I-N APD SSD SiPM 1.25 1 2 1 1
at pk 30% 80% 80% > 80% 60%
M 5 105 1 < 103 1 104-105
ENC/M 0 370 20 25 0
Energy Resolution
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
[email protected] – Prescott and Narayan, NIM A, 75 (1969)
B – G.Bizarri, IEEE TNS, Vol 53,02 (2006)
LaBr3(Ce)BNaI(Tl)A
W.Moses, NIM A, 487 (2002)
Luminosity (phe @ 662keV - PMT 25% QE)
CrystalNph/MeV
Nel
@ 662 keV
ER(%)@ 662 keV
ERscint.
(%)ERst
(%)ERnoise
(%)Light detector Ref.
NaI(Tl) 40000 6000 6.7 5.9 3.2 0 PMT typical
CsI(Tl) 65000 6000 6.6 5.8 3.2 0PMT
XP2254B PhilipsAllier (1998)
CsI(Tl) 65000 26000 4.3 3.8 1.5 1.2 SDD Fiorini (1997)
LaBr3(Ce) 63000 12000 3.6 2.2 2.5 0 PMT XP20Y0 Photonis Moszynski (2006)
LaBr3(Ce) 63000 19000 2.7 2.0 1.7 0.5 SDD Fiorini (2006)
LSO 2000 5300 8.8 7.8 3.6 0 PMT XP20Y0 Photonis Moszynski (2006)
BGO 9000 880 11.7 5.8 8.0 0 PMT XP20Y0 Photonis Moszynski (2006)
YAP 21000 10300 4.3 2.5 2.3 2.6APD –
6307073500 Adv.Phot.Inc.
Moszynski (2000)
Intrinsic Scintillator Energy Resolution
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Is the QE really useful?
Crystal Test: LaBr3:Ce Cylinder (½”Ø ½” thickness)
1 inch
1 inc
h
1° PMT HIGH QE:Hamamatsu R7600-200
QE max. = 41.6 % @ 380 nm Number of dinode = 10 Gain= 2.0 E+06 @ HV= -700 V
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
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Is the QE really useful?Pulse heigh Resolution & Coincidence
Resolving Time:
Crystal TEST: LSO 4 x 4 x 20 mm3 Source : Na22 (E @ 511keV)
PHR (%) CRT (psec)
PositionStandard
Type (QE=22%)
HIGH QE Type
Standard Type
(QE=22%)
HIGH QE Type
A 15.1 14.0 460 400
B 16.0 14.5 500 440
C 16.4 14.8 520 460
D 15.8 14.8 550 480
E 16.0 15.4 600 510
F 17.1 15.4 590 530
2° PMT HIGH QE:Hamamatsu R8900-00-C12
QE max. = 42 % @ 350 nm Number of dinode = 12 Gain= 1.0 E+06 @ HV= -800 V
PMT position
*Courtesy of Hamamatsu Photonics K.K. (Iwata City - Japan)
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Critical Angle & Q.E. :MC Simulation GEANT 4 Scintillation crystal : LaBr3:Ce continuous crystal
50 x 50 x 4 mm3 ( white entrance face – black edges) 8 8 Photodetector array ( 6.0 mm pitch) 140 keV photon energy
3 mm glass window Q.E = 0.22 – Phe n°=1153
No glass window Q.E = 0.60 – Phe n° = 5102
No glass window Q.E = 0.22 – Phe n°=1860
S.R.= 0.60 mmE.R. = 1.4 %
( 4.8 % including intrinsic energy resolution of LaBr3:Ce)
S.R.=0.82 mmE.R. = 5.1 %
( 6.9 % including intrinsic energy resolution of LaBr3:Ce)
S.R.= 0.75 mmE.R. = 2.3%
( 5.1 % including intrinsic energy resolution of LaBr3:Ce)
PD June 13-14 , 2007 Perugia - ItalyRoberto Pani
Conclusion
LaBr3:Ce seems a very promising crystal for SPET ( PET ToF)
application
Light sharing on continuous crystal requires position sensitive
photodetectors with superior performances
Intrinsic energy resolution of scintillators can seriously limit the energy
resolution response of a high Q.E. photodetectors
Removing glass window( critical angle) in scintillator coupling, could
strongly enhance imaging performances