CASCADED LINEAR-SYSTEMS ANALYSIS OF CMOS FLAT-PANEL DETECTORS FOR DIGITAL...
Transcript of CASCADED LINEAR-SYSTEMS ANALYSIS OF CMOS FLAT-PANEL DETECTORS FOR DIGITAL...
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Biomedical Mechatronics Lab
CASCADED LINEAR-SYSTEMS ANALYSIS
OF CMOS FLAT-PANEL DETECTORS
FOR DIGITAL RADIOGRAPHY
Seung Man Yun, Min Kook Cho,Chang Hwy Lim, Ho Kyung Kim*
School of Mechanical Engineering, Pusan National University, Republic of Korea
Thorsten GraeveRad-icon Imaging Corp., Belick street, Santa Clara, CA 95045-2404 USA
Hyosung ChoDepartment of Radiological Science, Yonsei University, Republic of Korea
Jung-Min KimCollege of Health Science, Korea University, Republic of Korea
ANDE 2007
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Motivation
• For better design and usage of various radiographic modalities▫ Computed tomography (CT), digital radiography (DR)
Biomedical Mechatronics Lab 2
Miniatured cone-beam CT system using CMOS flat-panel detector
SO 11-III [2007-494] October 19, 17:00
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
CMOS flat panel detector
• Photodiode arrays manufactured by CMOS process with scintillator▫ Smaller image lag and larger fill factor than a conventional amorphous
photodiode array
Biomedical Mechatronics Lab 3
Rad-icon RadEye1TM
Array format512 1024
pixels/1 detector
Pixel pitch 48 m
Field of view25 50
mm2/1 detector
Dynamic range 85 dB (>14 bits)
ADC bit-depth 12 bits
Pixel fill factor 0.87
Kodak Lanex Min-RTM
Composition Gd2O2S:Tb
Coverage 33.91 mg/cm2
Thickness 90 m
Density 3.77 g/cm3
RadEyeTM
Min-RTM
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
X-ray imaging system evaluation
Biomedical Mechatronics Lab 4
DQE
NPS
Resolution
Contrast
Noise
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Objectives
• Analyzing DQE of CMOS flat-panel detector for digital radiography▫ As a function of design parameters using cascaded model analysis
• Cascaded linear-systems theory-based modeling and simulation▫ Numerical modeling of NPS and DQE for x-ray imaging system evaluation
• Investigating a validity of the proposed cascaded model▫ Comparison with experimentally measured data for same condition
• Simulating DQE of the CMOS photodiode array with various design parameters▫ Photodiode quantum efficiency, fill factor, additive electronic noise
Biomedical Mechatronics Lab 5
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Evaluation procedure
Biomedical Mechatronics Lab 6
)(NNPS
)(MTF)(DQE
0
2
fq
ff
2D FFT
1D FFT
• Slit images• Gain-offset corrections
• Synthesizing LSF`s
• HVL measurements• Spectral simulation• Tuning kVp• Estimating fluence
• Scaling for non-uniformity• Averaging• Extracting 1D profiles
• White images• Gain-offset corrections• Detrending• Conversion into relative noise• Windowing
f
f
f
mmAl
I/I 0
spect
ral density
MTF
1
DQ
E
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Cascaded linear system analysis
• Cascade model describes the interacting of each process in detectors▫ The response of an system be linear and shift invariant (LSI), random noise
process be wide-sense stationary
Biomedical Mechatronics Lab 7
Stage Description Symbol Process
Incident X-ray q Uniform distribution
Quantum detection g1=AQBinomial selection
Quantum amplification g2=AMBinomial selection
Quantum scattering TscnStochastic blurring
Quantum conversion g4=ADBinomial selection
Aperture integration TapertDeterministic blurring
Sampling III Deterministic process
Additive noise saddDeterministic process
1g
2g
scnT 3
gapert
T III addσ signaldigital q
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
• DQE of cascaded linear-systems of the CMOS flat-panel detectors
Biomedical Mechatronics Lab 8
Fluence System gain
Noise power spectrum Additive electronic noise
System MTF
22
0
224
2222
σ)()(11
)()( )( )(DQE
addk
apertscn
M
DDMQ
apertscnDMQ
dd
kT
d
kT
I
AAAAAaq
TTAAAaq
ρρ
ρρρ
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Monte Carlo simulation
Biomedical Mechatronics Lab 9
Absorption Reflection
Refraction & transmission
Energy deposition& light conversionScintillator
Air gap = 1 m
Light photon detection plane
Spectral source sampling
MCNPXTM
DETECT2000TM
Polished surface
Grounded surface
Refractive index of phosphor = 2.6Absorption mfp. = 10 cmScattering mfp = 0.0017 cm
Pencil beam
Thin slap geometry: radius >> thickness
Subdividing the scintillatorinto thin sublayers to calculate the partial energy deposition and to estimate the escape probability of light photons with respect to the depth!!! Source
AED
OPD
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Experimental setup
• RQA 5 experimental condition (IEC 62220-1)
Biomedical Mechatronics Lab 10
Tube voltage 70 kVp (RQA5)
Tube current 0 ~ 125 mA
Exposure time at 1fps 550 ms
Source-to-detector distance 1000 mm
Added filter 21 mmAl
Added filter
Source-to-detector distance
X-raytube
CM
OS d
ete
ctor
surface
10 m wide slit camera(I.I.E. GmbH, Aachen, GER)
Slit camera
Ion chamber
Ion chamber(RAD-CHECK PLUS 06-526)
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Cascaded model simulation parameter
Biomedical Mechatronics Lab 11
Description Parameters
Pixel pitch d = 48 m
Pixel fill factor g = 87 %
pixel aperture a = 44.72 m
Incidence of X-ray q = 4.4×105 mm-2
Quantum absorption efficiency of screen AQ = 0.23
Average conversion efficiency of screen AM = 520
Quantum efficiency of photodiode AD = 0.55
Statistical swank factor I = 0.9
MTF of the scintillator Tscn( f ) = (1+1.0001f 2)-1
MTF due to the aperture integration Tapert( f ) = |sinc(af )|
Additive electronic noise sadd = 1100 e-
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Model validation
• Compared with Kodak Lanex Min-RTM screen (RQA 5, @50mA)
Biomedical Mechatronics Lab 12
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Effect of a photodiode quantum efficiency
Biomedical Mechatronics Lab 13
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Effect of a fill factor
Biomedical Mechatronics Lab 14
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Effect of a additive electronic noise
• The DQE is vulnerable to the additive noise than the other parameters
Biomedical Mechatronics Lab 15
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Conclusion
Biomedical Mechatronics Lab 16
• Cascaded linear-systems analysis of CMOS detector▫ Describes the signal and noise propagation
▫ Estimates its overall imaging performance
▫ Additive electronic noise is the most significant design parameter
• The developed model is a useful tool to design the CMOS flat-panel detector for digital radiography
• Based on this study, we can simulate a optimized design parameters of the CMOS photodiode array with scintillator