Transcript IWORID 2002

Flat X-ray Detectors
for Medical Imaging
Michael Overdick
Philips Research Laboratories, Aachen, Germany
IWORID 2002, Amsterdam, 11 Sept. 2002
Outline
• Flat Detector Technology
– Overview
– Key Components
• FD Performance
• Imaging Examples
• History & Future
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002
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Flat Detector Technology
Scintillator
ADC
Readout
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002
Addressing
3
Static detector: Digital Diagnost
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Dynamic detector: Integris Allura
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Scintillator: CsI:Tl needle crystals
• Thickness 550µm
 good X-ray
absorption
• Needles act as
light-guides
 sharp MTF
• CsI:Tl emits green
light
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Photodiode array: a-Si technology
• Same technology as
used in active
matrix LCDs
(TFT displays)
• a-Si photodiodes:
low dark currents,
high sensitivity
for green light
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Low noise readout electronics
• Driver and
readout chips
on flex modules
20 cm
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• Allowing very
compact designs
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Main noise sources in Flat X-ray Detectors
Shot noise from the
photodiode
(incl. refresh light)
TFT
switch
Gate
line
Photodiode
Common
electrode
Pixel circuit of
dynamic FD
Column
read-out
line
CSA
300 e-
Switching noise
(kTC-noise)
 750 e-
Amplifier noise
 800 e-
other (TFT etc.)
 600 e-
“Electronic noise”

PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002
approx. ENC
1300 e-
X-ray quantum
noise!
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Integris Allura
Flat Dynamic
Detector
for Cardio
Scintillator
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Photodiode array
Refresh light
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Technical Data
Digital Diagnost
Integris Allura FD
Detection
static
Field of view
43 cm x 43 cm
static + dynamic
(up to 30 frames/s)
18 cm x 18 cm
Number of pixels
3k x 3k
1k x 1k
Pixel size
143 µm x 143 µm 184 µm x 184 µm
DQE(0)
 60 %
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 75 %
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Detective Quantum Efficiency (DQE) for a
Flat Dynamic Detector
1
0.9
1000nGy
0.8
100nGy
10nGy
0.7
5nGy
DQE
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.5
1
1.5
2
2.5
-1
frequency [mm ]
From: F. Busse et al., Proc. SPIE 4320 (2001) 287-298
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DQE for a Static Flat Detector
DQE 0.8
Screen-film (400)
Fuji ST type V
Flat-panel detector
0.6
0.4
0.2
0
0
1
2
3
4
lp/mm
Source: PMS Hamburg
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Static FD performance
vs. Screen/Film systems
•
•
•
•
High DQE
Fully digital
Simple handling (no cassettes or films)
Large dynamic range
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X-ray film: Dynamic range
0.5 mAs
2 mAs
4 mAs
Under-exposed
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8 mAs
16 mAs
32 mAs
63 mAs
Over-exposed
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Flat detector: Dynamic range
typical usage
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Dynamic FD performance
vs. Image intensifiers (II-TV systems)
•
•
•
•
•
Larger dynamic range
Size & weight
Undistorted images
Immune to magnetic fields
Strongly reduced:
Veiling glare and fixed pattern noise
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Imaging examples
Dynamic FD: Heart arteries with contrast agent
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Imaging examples
Static FD: Shoulder and finger
1 cm
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History
1989
1993
1997
2000
2001
Start of FD Research Project at Philips
8”x8” FD Prototype
Joint venture with Thomson and Siemens (Trixell)
Introduction of static FDs by Trixell and GE Medical
Introduction of dynamic FDs for Cardio application
(GE Medical and Trixell)
Apart from CsI:Tl based FDs also Selenium based FDs
are availble (e.g. from Anrad/Toshiba), mainly used
for static applications (e.g. mammography).
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Future
• Flat Detectors for further applications and with
different sizes will enter the market.
• FDs will gradually replace II-TV systems.
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And what about CMOS Pixels?
CMOS Pixel Electronics
+ Amplifier in each pixel
+ Additional functionality
But:
• Cost and feasibility of large area CMOS coverage!
• Please carefully check against FD performance
(as the new “gold standard”)
Counting vs. Integrating:
• Nice topic for an extra talk!
• Observe the high maximal count rates ( 109 counts/s mm²)
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Conclusions
• Flat Detectors are out now in the market
(mainly static detectors and cardio detectors)
• FD technology offers various benefits
as compared to conventional systems.
• Scintillator, a-Si technology and low noise
electronics are the key FD ingredients.
• New X-ray detector developments should use
FD performance as their new benchmark.
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Acknowledgements
• Philips Medical Systems
(Best, Hamburg and North America)
• Trixell (Moirans, France)
• Colleagues at Philips Research Aachen and Redhill
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Residual signals
10
10
10
Normalized residual signal @ 21x30µGy
Normalized residual signal @ 30µGy
Dependence on the Refresh Light Duration
-2
-3
RLD=0µs g= -0.92
RLD=10µs g= -1.06
RLD=50µs g= -1.24
-4
10
-1
0
10
Time in s after exposure
10
1
10
10
10
-2
-3
RLD=0µs g= -0.74
RLD=10µs g= -0.77
RLD=50µs g= -0.83
RLD=250µs g= -0.89
-4
10
-1
0
10
Time in s after last exposure
10
1
 Stronger refresh light accelerates decay of Res. Signals
(M. Overdick et al., Proc. SPIE 4320 (2001) 47-58)
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