CASCADED LINEAR-SYSTEMS ANALYSIS OF CMOS FLAT-PANEL DETECTORS FOR DIGITAL...
Transcript of CASCADED LINEAR-SYSTEMS ANALYSIS OF CMOS FLAT-PANEL DETECTORS FOR DIGITAL...
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
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)
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Miniatured cone-beam CT system using CMOS flat-panel detector
SO 11-III [2007-494] October 19, 17:00
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
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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
Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
X-ray imaging system evaluation
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DQE
NPS
Resolution
Contrast
Noise
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
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Evaluation procedure
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)(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
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
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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
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
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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
Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Monte Carlo simulation
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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
Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Experimental setup
• RQA 5 experimental condition (IEC 62220-1)
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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)
Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Cascaded model simulation parameter
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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-
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)
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Effect of a photodiode quantum efficiency
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Effect of a fill factor
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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
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Cascaded Linear-systems Analysis of CMOS flat-panel detectors for digital radiography, ANDE 2007
Conclusion
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• 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