Flat X-ray Detectors for Medical Imaging

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Flat X-ray Detectors for Medical Imaging

• Michael Overdick
• Philips Research Laboratories, Aachen, Germany
• IWORID 2002, Amsterdam, 11 Sept. 2002

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Outline

• Flat Detector Technology
• Overview
• Key Components
• FD Performance
• Imaging Examples
• History Future

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Flat Detector Technology
Scintillator
ADC
Addressing
Readout
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Static detector Digital Diagnost
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Dynamic detector Integris Allura
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Scintillator CsITl needle crystals

• Thickness 550µm
• good X-ray absorption
• Needles act as light-guides
• sharp MTF
• CsITl 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
  sensitivityfor green light

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Low noise readout electronics

• Driver and readout chips on flex modules
• Allowing very compact designs

20 cm
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Main noise sources in Flat X-ray Detectors
TFT switch
Gate line
Photo- diode
Common electrode
Column read-out line
Pixel circuit of dynamic FD
CSA
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Integris AlluraFlat Dynamic Detectorfor Cardio
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Technical Data
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Detective Quantum Efficiency (DQE) for a Flat
Dynamic Detector
From F. Busse et al., Proc. SPIE 4320 (2001)
287-298
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DQE for a Static Flat Detector
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
8 mAs
0.5 mAs
2 mAs
4 mAs
16 mAs
32 mAs
63 mAs
Over-exposed
Under-exposed
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Flat detector Dynamic range
typical usage
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Dynamic FD performancevs. Image intensifiers
(II-TV systems)

• Larger dynamic range
• Size weight
• Undistorted images
• Immune to magnetic fields
• Strongly reducedVeiling glare and fixed pattern
  noise

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Imaging examplesDynamic FD Heart arteries with
contrast agent
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Imaging examplesStatic FD Shoulder and finger
1 cm
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History

• 1989 Start of FD Research Project at Philips
• 1993 8x8 FD Prototype
• 1997 Joint venture with Thomson and Siemens
  (Trixell)
• 2000 Introduction of static FDs by Trixell and
  GE Medical
• 2001 Introduction of dynamic FDs for Cardio
  application (GE Medical and Trixell)

Apart from CsITl 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 signalsDependence on the Refresh Light
Duration
Normalized residual signal _at_ 30µGy
Normalized residual signal _at_ 21x30µGy
g
RLD0µs
-0.74
g
g
RLD0µs
-0.92
RLD10µs
-0.77
g
g
RLD10µs
-1.06
RLD50µs
-0.83
g
g
RLD50µs
-1.24
RLD250µs
-0.89
Time in s after exposure
Time in s after last exposure
? Stronger refresh light accelerates decay of
Res. Signals
(M. Overdick et al., Proc. SPIE 4320 (2001) 47-58)