sensitivity study of the rpc–pet whole-body scanner
DESCRIPTION
Sensitivity Study of the RPC–PET whole-body scanner. M. Couceiro 1,2 , A. Blanco 1 , Nuno C. Ferreira 3 , R. Ferreira Marques 1,4 , P. Fonte 1,2 , L. Lopes 1. 1 LIP, Laboratório de Instrumentação e Física Experimental de Partículas, Coimbra, Portugal - PowerPoint PPT PresentationTRANSCRIPT
Sensitivity Study of the RPC–PET whole-body scanner
M. Couceiro1,2, A. Blanco1, Nuno C. Ferreira3,
R. Ferreira Marques1,4, P. Fonte1,2, L. Lopes1
1 LIP, Laboratório de Instrumentação e Física Experimental de Partículas,Coimbra, Portugal
2 ISEC, Instituto Superior de Engenharia de Coimbra, Coimbra, Portugal3 IBILI-FMUC, Instituto Biomédico de Investigação da Luz e Imagem, Faculdade de
Medicina, Coimbra, Portugal4 Departamento de Física, Universidade de Coimbra, Coimbra, Portugal
RPC-PETJornadas do LIP - 2008
Summary
Resistive Plate Chambers (RPCs)
Simulation Results of Sensitivity for Human Full-Body Axial Field Of View PET Systems
Conclusions
RPC-PETJornadas do LIP - 2008
XY readout plane
Y-strips
RC
passive netw
ork
RC passive network
X-strips
RPCs for PET
EResistive Cathode
Resistive Anode
At least one resistive electrode
e-
Photon
For 511 keV photons, and commonly used materials
~300 ps FWHM for photon pairs < 0.4% efficiency per gap for singles No energy resolution
Time signalHVSensitive Area
(precise small Gas Gap ~300 µm)
RPC-PETJornadas do LIP - 2008
Stacked RPCs
..........
e-
e-
e-
Improving Detection Efficiency
Efficiency depends both on Photon interaction probability in the
converter plate Electron extraction probability from
the converter plate
Converter plates with high interaction probabilityfor 511 keV photons
Optimize plate thickness for optimum electron extraction
RPC-PETJornadas do LIP - 2008
Plate Thickness (m)
Pho
ton
(511
keV
)D
etec
tion
Pro
babi
lity
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
10 100 1000
Glass
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
10 100 1000
Lead-Glass
Detection Efficiency: 511 keV Photons (GEANT4 Simulation)
Optimum efficiency is balanced by beam absorption (thicker plates) and extraction probability (thinner plates)
Optimum thickness depends on the number of plates and on the material. Optimum Thickness (µm)
N P
late
s
N Plates
Lead
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
10 100 1000
21
41
61
81
101
121
141
161
181
201
1001
Bateman et al.5 plates of 0.4 mm glass:Our measurements: 0.8% GEANT4 Simulation: 1.0%
RPC-PETJornadas do LIP - 2008
Detection Efficiency: Energy Dependence (GEANT4 Simulation)
Pho
ton
Det
ectio
n P
roba
bilit
y
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
100 200 300 400 500
Glass Lead-Glass
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
100 200 300 400 500
Incident Photon Energy (keV)
Lead
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
100 200 300 400 500
21
41
61
81
101
121
141
161
181
201
1001
N Plates
Strong ENERGY SENSITIVY scattered photons statistically rejected
Material
max Glass Lead-Glass Lead
N Plates 101 17% 29% 31%
201 29% 47% 50%
@ optimumthickness
@ optimumthickness
@ optimumthickness
RPC-PETJornadas do LIP - 2008
Disadvantages Much smaller detection efficiency: 20% to 50%. No energy resolution, although energy sensitivity.
Advantages
Increased position accuracy Sub-millimetric spatial resolution Full 3D detection
Increased system sensitivity Inexpensive Large areas possible
large solid angle coverage Excellent timing resolution (300 ps FWHM for 511 keV
photon pair) TOF-PET Optimum randoms rejection
Comparison With the Standard PET Technology
Possible specialized
PET applications
Full-BodyHuman
TOF-PET
RPC-PETJornadas do LIP - 2008
Human Full Body FOV RPC–PET: Sensitivity Advantage
Main Goals Study the sensitivity gain for large Axial Field Of View human PET systems (> 200 cm)
Crystal based RPC based
Comparison with commercial scanners (e.g. GE Advance)
Methods Simple analytical model for the sensitivity to true coincidences GEANT4 simulations of photon transport through sensitivity phantoms (NEMA NU2 1994
and an extended version) Photon interaction within detectors not simulated Post processing of detection and coincidences (detection efficiency, packing fraction,
energy blurring, energy window, coincidence window, etc.): Scintillator based detectors RPC based detectors
3D true sensitivity computation followed the NEMA NU2 1994 procedure
RPC-PETJornadas do LIP - 2008
d
d
x1
x2
1 2
2( ) / cos( ( ))
20 0
1( )
dn x x Z zT Z z e d d
d
Emitting Point
Human Full Body PET Sensitivity: Simplified Analytical Model
2
1 1
202 2
32 22
2
2
z
Z z
R T Z zS d dz dZ
R Z z
1 max 2 , tanz L Z R
2 min 2 , tanz L Z R
1 max 2, 2Z L
L
Water Phantom
Z
z
d
R
2L Z 2L Z
2 2
r
ds
Tomograph
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Human Full Body PET Sensitivity: Simulation Setups
(a) 15 cm AFOV by 92.7 cm ØNEMA NU 2 1994 sensitivity phantom
(b) 15 cm AFOV by 92.7 cm Øwith an extended phantom
(c) 240 cm AFOV by 92.7 cm Øwith an extended phantom
(a)
(b) (c)
RPC-PETJornadas do LIP - 2008
Human Full Body PET Sensitivity: Validation for Crystal Based Systems
3D True Sensitivity (kcps/(µCi/cc))
Lewellen et al. This Simulation
Ring Difference NEMA NU2 1994 PhantomExtended Phantom
11 1020 1013 (-0.7%) 1032 (+1.2%)
17 1240 1160 (-6.5%) 1180 (-4.8%)
Data processing Photons assigned to a Module/Block/Crystal according to the GE Advance segmentation Gaussian energy blurring with 20% FWHM at 511 keV 300 – 650 keV energy window Detection efficiency adjusted to obtain reasonable agreement with published data.
RPC-PETJornadas do LIP - 2008
Human Full Body PET Sensitivity: Results for Crystal Based Systems
~100-fold sensitivity advantage for standard PET without TOF? ~300-fold sensitivity advantage for LSO based PET with TOF ?
0
20
40
60
80
100
120
0 30 60 90 120 150 180 210 240
AFOV (cm)
Rel
ativ
e 3D
Tru
e S
ensi
tivi
ty
Simulated Data - 5.7 deg
Simulated Data - 15 deg
Simulated Data - 30 deg
Simulated Data - 45 deg
Simulated Data - Full Acceptance
Analitical Model - 5.7 deg
Analitical Model - 15 deg
Analitical Model - 30 deg
Analitical Model - 45 deg
Analitical Model - Full Acceptance
0
5
10
15
0 15 30 45 60
+ Badawi et al.normalized
Normalized to the GE Advance sensitivityring difference of 11 (axial acceptance angle ~5.7 deg)
RPC-PETJornadas do LIP - 2008
Human Full Body AFOV PET
Full Body AFOV Crystal Based PET Scanners Maintaining crystal thickness for full body AFOV PET scanners
unaffordable Keeping overall crystal volume, reducing crystal thickness
reduce detection efficiency, and sensitivity
RPC TOF-PET Scanners?
RPC-PETJornadas do LIP - 2008
Human Full Body RPC TOF–PET Sensitivity: Selected Efficiencies
y = -1,96E-16 x6 + 3,39E-13 x5 - 2,29E-10 x4 + 7,62E-08 x3 - 1,19E-05 x2 + 8,95E-04 x - 7,05E-03
R2 = 1,00E+00
y = -1,62E-16 x6 + 2,86E-13 x5 - 1,97E-10 x4 + 6,56E-08 x3 - 1,02E-05 x2 + 6,99E-04 x - 5,15E-03
R2 = 1,00E+00
0,00
0,05
0,10
0,15
0,20
0 100 200 300 400 500
60 Plates
120 Plates
Polinómio(60 Plates)
Incident Photon Energy (keV)
Pho
ton
Det
ectio
n E
ffic
ienc
y
Efficiencies of 60 and 120 stacked RPCsbased on 0.4 mm glass plates
19.4%
11.0%
RPC-PETJornadas do LIP - 2008
Human Full Body RPC TOF–PET Sensitivity: Simulation Results
200~ 4.4
( / 2) 45TOF
L mmg
c t mm
t = 300 ps FWHM
With TOF information
~20-fold sensitivity increase
Axial Field of View (cm)
3D T
rue
Sen
sitiv
ity (
kcps
/(µ
Ci/c
c))
0
5000
10000
15000
20000
25000
30000
0 30 60 90 120 150 180 210 240
GE Advance - 11 Rings (Lewellen et al)
GE Advance - 11 Rings (simulation)
GE Advance - 17 Rings (Lewellen et al)
GE Advance - 17 Rings (simulation)
60 Plates - 5.7 degrees
60 Plates - 15 degrees
60 Plates - 30 degrees
60 Plates - 45 degrees
60 Plates - Full Acceptance
120 Plates - 5.7 degrees
120 Plates - 15 degrees
120 Plates - 30 degrees
120 Plates - 45 degrees
120 Plates - Full Acceptance
GE Advance(max. ~1240 kcps/(µCi/cc))
RPC-PETJornadas do LIP - 2008
Human Full Body RPC TOF–PET Scatter Fraction: Simulation Results
Moderate excess of scatter over most
standard PET systems
Scatter Important source of
image noise; Typically rejected by
energy discrimination.
0%
10%
20%
30%
40%
50%
0 50 100 150 200 250
GE Advance
60 Plates
120 Plates
Sca
tter
Fra
ctio
n in
Ful
l A
ccep
tanc
e M
ode
Axial Field of View (cm)
RPC Energy Sensitivity
Incident Photon Energy (keV)
Eff
icie
ncy
0%
5%
10%
15%
20%
25%
30%
0 100 200 300 400 500
20 4060 80100 120140 160180 200
Number of 0.4 mm Glass Plates
RPC-PETJornadas do LIP - 2008
Conclusions
Full-body AFOV sensitivity ~20 fold sensitivity gains for 240 cm AFOV RPC TOF-PET may be attainable Scatter is partially rejected by detector energy sensitivity
RPC application to PET seems possible in Full-body human PET, offering larger throughput - hopefully without extra cost
Comprehensive study of a full system in progress A first detector has been assembled and Luís Lopes in his talk will show the
detector details, and present some preliminary results obtained with it