Nityanand gopalika digital detectors for industrial applications

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This is a presentation by Nityanand Gopalika on Digital Radiograpgy. The presentation we given @ Digital Radiography workshop organized by GE at JFWTC, Bangalore.

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Nityanand gopalika digital detectors for industrial applications

  1. 1. Digital Radiography:a-Si Array Detectors for Industrial ApplicationsNityanand Gopalika, D. Mishra, V. Manoharan & Greg Mohr* Industrial Imaging and Modeling Laboratory John F Welch Technology Center Bangalore *GE Inspection Technologies One Neumann Way MD K207 Cincinnati, OH 45215
  2. 2. Presentation Outline:• Technology Development• Benefits of Digital Radiography• Quantifying Image Quality• Image Quality Metric for Digital Systems• Comparison of Imaging Devices: CCD, CMOS and a-Si• Performance Study of Flat Panels
  3. 3. Technology Development NDT World Film radiography Productivity Resolution Image intensifiers Computed radiography Cost Size CCD technology Direct digital radiography Evolution of Direct Digital X-ray Detectors 3/ Industrial Imaging and Modeling Laboratory
  4. 4. Benefits of Digital RadiographyProductivity• Faster response• Elimination of chemical processing• Automated inspection• Elimination of retakesCost• Elimination film and consumables• ROI in two to three yearsQuality• Image processing and analysis• Reduces operators fatigue• ConsistencyAdvanced Application• Volumetric CT for High Throughput Productivity and cost benefits 4/ Industrial Imaging and Modeling Laboratory
  5. 5. Quantifying Image Quality What is a good Physical Measure of Increasing Contrast Image Quality? Contrast-to-Noise Ratio Perceived Image Quality Decreasing Noise Measure of Image Quality 5/ Industrial Imaging and Modeling Laboratory
  6. 6. Image Quality Metric for Digital Systems MTF: Same Response to Signal and Noise 6/ Industrial Imaging and Modeling Laboratory
  7. 7. Image Quality Metric for Digital Systems MTF LimitationsContrast  Limiting Spatial Resolution (LSR), MTF measured at high contrast • bar patterns » 100% input contrast  MTF indicates fraction of signal that will be seen in image.Noise  MTF measured under noiseless conditions.  MTF transfers noise in addition to signal.  Image noise can interfere with object detectability. Higher MTF Does Not Mean Better Imaging System 7/ Industrial Imaging and Modeling Laboratory
  8. 8. Image Quality Metric for Digital Systems MTF: High Middle Low SNR = 1 High MTF Middle Higher limiting resolution of smaller Low pixels may not provide better detectability in noisy images. High MTF; But Poor Performance 8/ Industrial Imaging and Modeling Laboratory
  9. 9. Image Quality Metric for Digital Systems• Quantum and electronic noise are unavoidable in digital imaging chain.• SNR can vary widely across systems• High SNR is key to better inspection power• To increase SNR often the only way is to increase radiation dose, unacceptable trade-off• Achieving high SNR at lower dose: better imaging system Traditional gauge used for quantifying image quality cannot be used as a stand alone metric. MTF is One Metric; But Not Enough 9/ Industrial Imaging and Modeling Laboratory
  10. 10. Image Quality Metric for Digital Systems DQE: Detective Quantum Efficiency SNR2 at detector output DQE = SNR2 at detector input SNR = signal-to-noise ratio Measure of SNR transmittance 10 / Industrial Imaging and Modeling Laboratory
  11. 11. Image Quality Metric for Digital SystemsInput SNR2 proportional to radiation dose Image Quality DQE α Input Radiation Dose• Traditional measures such as MTF, LSR are not sufficient to characterize detector performance• Noise is a limiting factor for detectability, image processing, and advanced applicationsDoubling DQE means:• Same output SNR (“image quality”) at half the dose• 40% improvement in SNR at same dose Less Dose and Better Image 11 / Industrial Imaging and Modeling Laboratory
  12. 12. Image Quality Metric for Digital Systems “Improved” “Standard” “Object” DQE = 0.5 DQE = 0.25 SNR = 5 SNR = 3.5 SNR = 2.5 High DQE at Lower Dose 12 / Industrial Imaging and Modeling Laboratory
  13. 13. Image Quality Metric for Digital Systems Film GE Detector High DQE  Better Detectability 13 / Industrial Imaging and Modeling Laboratory
  14. 14. Image Quality Metric for Digital Systems Detector Design Keeping DQE in Mind 14 / Industrial Imaging and Modeling Laboratory
  15. 15. Detector Design for High DQE The Detector Measurements One Properties and Requirements Image Quality Measure Pixel Size MTF Sampling, Fill Factor, Aliasing High Resolution (for small object detection) Scintillator/ Coupling Signal (S) DQE CsI, Lanex, Se lens/Direct Efficient X-Ray Conversion 1 S 2 ⋅ MTF 2 (for minimum exposure) DQE = Photodetector Q NPS aSi, CCD, CMOS Noise (NPS) Readout Low Noise (for clear visualization) Electronic Noise 15 / Industrial Imaging and Modeling Laboratory
  16. 16. Flat Panel Technology Direct Conversion (Se) Indirect Conversion (CsI) Photons Photons Cesium Iodide (CsI) Selenium Light Amorphous Silicon Panel Electrons Electrons Read Out Electronics Read Out Electronics Digital Data Digital Data Flat Panel Technology Variation 16 / Industrial Imaging and Modeling Laboratory
  17. 17. CsI vs. SeCesium Iodide Selenium• Very high DQE; potential for high • Direct conversion of X-Ray into image quality at low dose electrical signals• Fluoro capable • Currently not capable of fluoro• Advanced application capable • Low X-Ray absorption• Mature technology: 25-year history • High sensitivity to temperature with Image Intensifiers Again Keep DQE in Mind!! 17 / Industrial Imaging and Modeling Laboratory
  18. 18. Point Spread Function for DifferentDetector Types Electrons Image Intensifiers CSI Flat panels Se Flat panels MTF is One Part of the Story, DQE is the Other BIG Part 18 / Industrial Imaging and Modeling Laboratory
  19. 19. CCD Technology Photons Scintillator Light Fiber Optic Taper CCD Electrons Amorphous Silicon CCD• Potentially high image quality at low • CCDs are easily available dose (high DQE) • Low development costs• Active Research on New Applications • “Transition” technology to• Designed for X-Ray from the start flat panel• Compact packaging • High CCD cost• Very high development cost • Tiling and design complexity 19 / Industrial Imaging and Modeling Laboratory
  20. 20. Silicon Imaging Devices, CCD, CMOS &a-Si Imager Dimensions • CCDs: 10 – 60-mm on a side • CMOS: 50-mm on a side • a-Si: 200 – 410-mm on a side Size governed by silicon process • CCDs and CMOS – 6” wafers • Multiple chips/wafer – yield • a-Si – Large area deposition/glass Pixel Dimensions • CCDs: 9 – 25 microns • CMOS: 40 – 50 microns • a-Si: 100 – 400 microns • Pixel size governed by architecture All will convert visible energies into an electronic charge 20 / Industrial Imaging and Modeling Laboratory
  21. 21. Silicon Imaging Devices, CCD, CMOS &a-Si Coupling device Phosphor or Silicon Device Photoconductor or Method Fiber optic coupler Requires 10X more Exposure CCD or CMOS Requires 100X more Exposure Lens Fiber optic scintillator and/or Shielding Cooled CCD phosphor Glass Camera 21 / Industrial Imaging and Modeling Laboratory
  22. 22. GE Digital X-Ray Detectors3 Types of GE Digital X-Ray PanelsAll feature high efficiency & fast 14-bitreadoutHighest resolution (DXR-500) • 7” x 9” (19 cm x 23 cm) @ 100 micron • Over 20% MTF at 5 lp/mmHighest efficiency (DXR-250) • 16” x 16” (41 cm x 41 cm) @ 200 micronFastest Imaging (DXR-250RT) • Up to 30 Hz • 8” x 8” (20 cm x 20 cm) @ 200 micron Panels Optimized for Different Applications 22 / Industrial Imaging and Modeling Laboratory
  23. 23. Performance Study: Radiation Exposure DXR-500 DR system 14000 12000 Signal(ADC) 10000 8000 6000 4000 2000 0 0 5 10 15 20 25 30 35 Relative exposure Comparative study Useful exposure range Industrial X-ray filmCharacteristics DXR-500 Digital Detector ( Medium speed) Min and Max exp ratio 2 In the order of few mR to get 1.3 R to get Optical Productivity: Speed signal level of 12000 density of 2 Useful minimum to • High Speed (mR vs. R) Useful minimum toDynamic range maximum exposure • Minimized Rework maximum exposure ratio 12 ratio 2 • High Latitude CoverageTypical Exposure ratio requirements Advantages • Less radiation field X-ray tube Subject Material Lattitude potential contrast • Micro focus (Faster response Ti 3 to 20 mm 160 kV 12.7 enables high definition Steel 1 to 10 mm 160 kV 7.28 radiography) Detector Characteristics Suitable for Industrial Applications 23 / Industrial Imaging and Modeling Laboratory
  24. 24. Dynamic range Ti step wedge image 2 –20 mm • High latitude coverage1 • ~ 10 times > image- intensifier2 • No blooming or saturation3 • Window leveling 2& 3 window level • No Lead masking adjusted Wide dynamic range enables- high latitude imaging 24 / Industrial Imaging and Modeling Laboratory
  25. 25. Artifacts Source:GE Health care Source:GE Health care Image Intensifier- distortion Flat panel- no distortion > No distortion Flat panel XII > No blooming > Uniform sensitivity Source:GE Health care over entire area Brightness uniformity > Brightness uniformity 25 / Industrial Imaging and Modeling Laboratory
  26. 26. Performance study-Spatial resolution FS = 1.8 mm FS = 0.4 mm Observation: • System can be designed to match with film MTF. • Digital detector with mini/micro focal tube outperforms film radiography with large focal spots. • DQE of DXR-500 is comparatively good. FS = 1.8mm System Design for Meeting Requirements FS = 0.4 mm 26 / Industrial Imaging and Modeling Laboratory
  27. 27. Detective quantum efficiency Source: GE healthcare DQE comparison- XII vs. DR Better defect detectability in useful spatial resolution range 27 / Industrial Imaging and Modeling Laboratory
  28. 28. Performance study-Noise response • Poisson distributed noise • Noise Quantum limited • Averaging of frames reduces noise Effect of no. of frames 5 frames Effect of no. of X-ray photons 1 mAs 10 frames 20 frames 5 mAs Quantum Limited Noise Performance 28 / Industrial Imaging and Modeling Laboratory
  29. 29. Performance study-IQI sensitivity Mat. – Ti Mat. – SS Mat. – Al Mat. – Ti Thick. – 25mm Thick. – 10mm Thick. – 40 mm Thick. – 10mm KVp – 120 KVp– 140 KVp – 120 KVp – 120 mAs – 1.0 mAs – 1.0 mAs – 1.0 mAs – 1.0 FS – 0.4 mm FS – 0.4 mm FS – 0.4 mm FS – 0.4 mm 2-1T sensitivity over range of thickness 29 / Industrial Imaging and Modeling Laboratory
  30. 30. Performance study-Imaging 2-2T Porosity SensitivityLack ofpenetrationKVp – 125mAs – 1.0FS – 0.4mmMat. – CSI KVp – 125 Mat. – CS mAs – 1.0 FS – 0.4 mm Range of applications with 2-1T sensitivity Imaging and Modeling Laboratory/ Industrial 30
  31. 31. Performance study-Imaging Object – IC KVp – 70 mAs – .5 FS – 10 microns Mag. – 50X Object – IC Object –ceramics KVp – 70 KVp – 70 mAs – .5 mAs – .5 FS – 10 microns FS – 10 microns Mag. – 50X Mag. – 50X 31 / Enable high definition radiography Industrial Imaging and Modeling Laboratory
  32. 32. Welding defects-Lack of penetrationand spatter Material: CS Plate, 12 mm thk SW SI – Offset FS-0.4 mm SDD-700 mm KVp: 130, 2 mAs Filter: Cu –0.4 mm 32 / Industrial Imaging and Modeling Laboratory
  33. 33. Summary• System can be designed to meet image quality requirements• Quantum limited noise performance• Faster response and wide dynamic range• Real time (fluoro)• Range of applications with 2-1T sensitivity• Enables high definition radiography• Advanced image processing for image optimization 33 / Industrial Imaging and Modeling Laboratory

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