Post on 12-Aug-2020
transcript
Computed Radiography System
Simulation Focusing on the Optical
Readout Process
Min YAO INSA de Lyon
Valérie KAFTANDJIAN INSA de Lyon
Philippe DUVAUCHELLE INSA de Lyon
Angéla PETERZOL-PARMENTIER AREVA
Andreas SCHUMM EDF
Peter WILLEMS GE
Juin 22, 2015
Digital Industrial Radiology and Computed Tomography (DIR 2015) 22-25 June 2015, Belgium, Ghent - www.ndt.net/app.DIR2015
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Outline
1. Computed radiography principle, advantages and
limitations
2. Optical readout simulation
Involved phenomena
Simulation method
– Laser spreading inside imaging plate (Monte Carlo tool)
– Laser scanning (Analytical model)
3. Illustration of different optical effects
4. Conclusion
3 / 18
What is Computed Radiography (CR)?
Imaging Plate Moved Translationally
Laser
ADCDigitizedSignal
2.Readout
3.Erasure
Intense Light
1.X-Ray Exposure
IPirradiation
Imaging Plate (IP)
Latent image
X-ray source
object
4 / 18
Advantages and limitations
• Advantages
+ Flexibility of detector
+ Direct digital image
+ Reusability
+ High dynamic range up to 105
• Limitations
- Poor efficiency at high energies
- Poor spatial resolution
due to the optical readout process
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Objective
• CR imaging chain modeling
Exposure Readout
Source
object
detector
ScannerX-ray
Latent imageX-ray CR final imageLatent image
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Optical readout simulation: involved phenomena
Imaging Plate Moved Translationally
Laser
ADC DigitizedSignal
Scan (Laser Beam) Direction
Sub-s
can (
Pla
te
Tra
nsla
tion)
Direction
* AAPM Task Group 10 (2006)
• Flying spot scanner
Latent image read by a scanning laser
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Optical readout simulation: involved phenomena
• Static laser
Photo-stimulation by laser beam
Light emission: photo-stimulated luminescence (PSL)
Laser beam
Support
Protective layer
PSL
Phosphor layer
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• Scanning laser
PSL emission
Latent image
modification
PSLLaser
t+Δt
PSLLaser
t+2Δt
PSLLaser
t+3Δt
Optical readout simulation: involved phenomena
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• Analytical operator using a Monte Carlo optical response model
Optical readout simulation: method
H2
Latent image
Limg(x,y,z)
CR final imageDimg(x,y)
Optical response
model f(x,y,z)
Scanning
parameters
PSLLaser
PSLLaser
PSLLaser
),,(),( 2 parametersscanningfLimgHyxDimg nm
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yx
scanlasernm
z
nm
dxdytPzyyxxfzyxLimgdzzP
parametersscanningfLimgHyxDimg
,
(mod)
2
),,(exp1),,()(
),,(),(
Optical readout simulation: method
latent image
modified by
scanning
optical cross
section of
photostimulation
optical response
(Monte Carlo)
PSL
detection
probability
Scanning
parameters
* Modified fromThoms (1996)
11 / 18Radius (m)
De
pth
(
m)
-200 -100 0 100 200
0
50
100
150
La
se
r d
istr
ibu
tio
n (
cm
-2)
2
4
6
8
10
x 106
Optical readout simulation: method
• Monte Carlo tool to obtain the optical response f(x,y,z)
IP is described by
Absorption coefficient
Scattering coefficient
Anisotropic factor :
– Forward peaked scattering
– Isotropic
– ...
Boundary conditions
• Output
light intensity function f(x,y,z)
Laser
f(x,y,z)
* Wang et al. (1995)
Fasbender et al. (2003)
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100 200
Different optical effects illustration: absorption coefficient
• Great absorption coefficient: small scattering region
Bad efficiency, good resolution
100 times higher absorptionreference
-200 -100200
150
100
50
0
-200 -100200
150
100
50
0
Laser
-200 -100200
150
100
50
0
50
100
150
200
250
300
350
400
Intensity
IP d
epth
(µ
m)
Radius (µm)
I(x,y,z)
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100 200
-200 -100200
150
100
50
0
• Forward peaked scattering: great penetration depth
Good efficiency, good resolution
Different optical effects illustration: anisotropy factor
Forward peaked scattering
Laser
reference
-200 -100200
150
100
50
0
50
100
150
200
250
300
350
400
IP d
epth
(µ
m)
Radius (µm)
Intensity
-200 -100200
150
100
50
0
I(x,y,z)
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Different optical effects illustration: laser intensity
• Great intensity: great penetration depth
Good efficiency, bad resolution
2 times more intensity
100 200
Laser
reference
-200 -100200
150
100
50
0
-200 -100200
150
100
50
0
50
100
150
200
250
300
350
400
IP d
epth
(µ
m)
Radius (µm)
-200 -100200
150
100
50
0 Intensity
I(x,y,z)
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Different optical effects illustration: IP thickness
• Small thickness: small scattering region
Bad efficiency, good resolution
Small thickness
100 200
Laser
reference
-200 -100200
150
100
50
0
-200 -100200
150
100
50
0
50
100
150
200
250
300
350
400
IP d
epth
(µ
m)
Radius (µm)
-200 -100200
150
100
50
0 Intensity
I(x,y,z)
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Different optical effects illustration: scanning effect
x (mm)
y (
mm
)
-1 -0.5 0 0.5 1
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1 15.2
15.4
15.6
15.8
16
16.2
16.4
16.6
16.8
17Readout factor1010
x (mm)
y (
mm
)
-1 -0.5 0 0.5 1
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1 660
670
680
690
700
710
720
730
Readoutfactor1016
x (mm)
y (
mm
)
-1 -0.5 0 0.5 1
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
13.8
3.85
3.9
3.95
4
4.05
4.1
4.15
4.2
4.25
x 104
Limg
x 104
Readout factor= Laser power × scanning time
Example of latent image (reference test object with various holes)
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-10 -8 -6 -4 -2 0 2 4 6 8 100.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1
y (mm)
No
rma
lize
d p
rofi
le
Latent image
1e10
1e16
-10 -8 -6 -4 -2 0 2 4 6 8 100.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1
y (mm)
No
rma
lize
d p
rofi
le
Latent image
1e10
1e16
-10 -8 -6 -4 -2 0 2 4 6 8 100.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1
y (mm)
No
rma
lize
d p
rofi
le
Latent image
1e10
1e16
• Influence of readout factor
Different optical effects illustration: scanning effect
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Conclusion
• Simulation of optical readout process combining
analytical and MC tool
Interest of the tool
→ study of different optical effects
– absorption and scattering factors, IP thickness …
– scanning parameters
Modeling of the complete CR system is now available
→ in use at industrial site AREVA and EDF
To be done in the future : structural noise of IP
Thank you for your attention!