Flat X-ray Detectors for Medical Imaging Michael Overdick Philips Research Laboratories, Aachen, Germany IWORID 2002, Amsterdam, 11 Sept. 2002.
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Flat X-ray Detectors for Medical Imaging
Michael Overdick Philips Research Laboratories, Aachen, Germany
IWORID 2002, Amsterdam, 11 Sept. 2002
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 2
Outline
• Flat Detector Technology– Overview
– Key Components
• FD Performance
• Imaging Examples
• History & Future
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 3
Flat Detector Technology
Scintillator
AddressingReadout
ADC
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 4
Static detector: Digital Diagnost
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 5
Dynamic detector: Integris Allura
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 6
Scintillator: CsI:Tl needle crystals
• Thickness 550µm
good X-ray absorption
• Needles act as light-guides
sharp MTF
• CsI:Tl emits green light
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 7
Photodiode array: a-Si technology
• Same technology as used in active matrix LCDs (TFT displays)
• a-Si photodiodes: low dark currents,high sensitivityfor green light
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 8
Low noise readout electronics
• Driver and readout chips on flex modules
• Allowing very compact designs
20 cm
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 9
Main noise sources in Flat X-ray Detectors
Commonelectrode
CSA
TFTswitch
Photo-diode
Gateline
Columnread-out
line
Switching noise (kTC-noise) 750 e-
Amplifier noise 800 e-
X-ray quantum noise!
“Electronic noise” 1300 e-
other (TFT etc.) 600 e-
Shot noise from the photodiode (incl. refresh light)
300 e-
approx. ENC
Pixel circuit ofdynamic FD
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 10
Integris AlluraFlat Dynamic Detectorfor Cardio
Scintillator Photodiode array Refresh light
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 11
Technical Data
Digital Diagnost Integris Allura FD
Detection static static + dynamic(up to 30 frames/s)
Field of view 43 cm x 43 cm 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 % 75 %
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 12
Detective Quantum Efficiency (DQE) for a Flat Dynamic Detector
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5
frequency [mm-1]
DQ
E
1000nGy
100nGy
10nGy
5nGy
From: F. Busse et al., Proc. SPIE 4320 (2001) 287-298
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 13
DQE for a Static Flat Detector
0 1 2 3 4
lp/mm
0
0.2
0.4
0.6
0.8DQE
Screen-film (400)Fuji ST type VFlat-panel detector
Source: PMS Hamburg
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 14
Static FD performance vs. Screen/Film systems
• High DQE• Fully digital• Simple handling (no cassettes or films)• Large dynamic range
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 15
X-ray film: Dynamic range
Over-exposedUnder-exposed
8
mAs
0.5
mAs
2
mAs
4
mAs
16
mAs
32 mAs 63
mAs
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 16
Flat detector: Dynamic range
typical usage
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 17
Dynamic FD performancevs. Image intensifiers (II-TV systems)• Larger dynamic range• Size & weight• Undistorted images• Immune to magnetic fields• Strongly reduced:
Veiling glare and fixed pattern noise
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 18
Imaging examplesDynamic FD: Heart arteries with contrast agent
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 19
Imaging examplesStatic FD: Shoulder and finger
1 cm
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 20
History
1989 Start of FD Research Project at Philips1993 8”x8” FD Prototype1997 Joint venture with Thomson and Siemens (Trixell)2000 Introduction of static FDs by Trixell and GE Medical2001 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).
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 21
Future
• Flat Detectors for further applications and with different sizes will enter the market.
• FDs will gradually replace II-TV systems.
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 22
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)
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 23
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.
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 24
Acknowledgements
• Philips Medical Systems (Best, Hamburg and North America)
• Trixell (Moirans, France)
• Colleagues at Philips Research Aachen and Redhill
PFL-Aachen, M. Overdick, 11 Sept 2002, IWORID 2002 26
Residual signalsDependence on the Refresh Light Duration
10-1
100
101
10-4
10-3
10-2
Time in s after exposure
Nor
mal
ized
res
idua
l sig
nal @
30µ
Gy
RLD=0µs g= -0.92 RLD=10µs g= -1.06RLD=50µs g= -1.24
10-1
100
101
10-4
10-3
10-2
Nor
mal
ized
res
idua
l sig
nal @
21x
30µ
Gy
Time in s after last exposure
RLD=0µs g= -0.74 RLD=10µs g= -0.77 RLD=50µs g= -0.83 RLD=250µs g= -0.89
Stronger refresh light accelerates decay of Res. Signals
(M. Overdick et al., Proc. SPIE 4320 (2001) 47-58)
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