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Imaging Properties of the Medipix2 System exploiting Single and Dual Energy Thresholds

Imaging Properties of the Medipix2 System exploiting Single and Dual Energy Thresholds. L. Tlustos 1 , R. Ballabriga 1 , M. Campbell 1 , E. Heijne 1 , k Kincade 2 , X. Llopart 1 , P. Stejskal 3 1 Ph Department, CERN, Geneva, Switzerland 2 University of Canterbury, Christchurch, New Zealand

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Imaging Properties of the Medipix2 System exploiting Single and Dual Energy Thresholds

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  1. Imaging Properties of the Medipix2 System exploiting Single and Dual Energy Thresholds L. Tlustos1, R. Ballabriga1, M. Campbell1, E. Heijne1, k Kincade2, X. Llopart1, P. Stejskal3 1 Ph Department, CERN, Geneva, Switzerland 2 University of Canterbury, Christchurch, New Zealand 3 Institute of Experimental and Applied Physics, Technical University of Prague, Czech Republic.

  2. The Medipix2 Consortium • Institut de Fisca d'Altes Energies, Barcelona, Spain • University of Cagliari and INFN Section thereof, Italy • CEA, Paris, France • CERN, Geneva, Switzerland, • Universitat Freiburg, Freiburg, Germany, • University of Glasgow, Scotland • Universita' di Napoli and INFN Section thereof, Italy • NIKHEF, Amsterdam, The Netherlands • University of Pisa and INFN Section thereof, Italy • University of Auvergne, Clermont Ferrand, France, • Laboratory of Molecular Biology, Cambridge England • Mitthogskolan, Sundsvall, Sweden, • Czech Technical University, Prague, Czech Republic • ESRF, Grenoble, France • Academy of Sciences of the Czech Republic, Prague • Universität Erlangen-Nurnberg, Erlangen, Germany • University of California, Berkeley, USA Michael Campbell

  3. Outline • Motivation and a brief overview of the Medipix2 system • MTF, NPS and DQE for a single photon counting system as a function of lower threshold • Imaging of an object using the energy window • Concluding remarks Michael Campbell

  4. Introduction and Motivation • Single photon counting provides clean images across a wide range of incoming photon fluxes • Flexible – many applications • Energy selective x-ray imaging possible • MTF, NPS and DQE as a function of threshold - Medipix2 readout chip and a 300 mm thick Si sensor • First energy selective images of an object using a polychromatic source Michael Campbell

  5. Hybrid Pixel Detector Detector and electronics readout are optimized separately Michael Campbell

  6. Hybrid Pixel Detector - Cross Section Michael Campbell

  7. Medipix2 Cell Schematic Charge sensitive preamplifier with individual leakage current compensation 2 discriminators with globally adjustable threshold 3-bit local fine tuning of the threshold per discriminator 1 test and1 mask bit External shutter activates the counter 13-bit pseudo-random counter 1 Overflow bit Michael Campbell

  8. Medipix2 Cell Layout Michael Campbell

  9. Medipix2 Chip Architecture 256 x 256 pixels 10ms readout time Michael Campbell

  10. Medipix2 bump bonded to a 300mm Si sensor Michael Campbell

  11. Bumps of readout side Michael Campbell

  12. Bumps of readout side – close up Michael Campbell

  13. 90Sr source scanned in real time 20 frames per second – limited by DAQ not chip Michael Campbell

  14. Calculated incoming spectrum and position of thresholds used Thresholds 9.1 keV 11.3 keV 12.8 keV 18.8 keV Siefert FK-61-04x12 X-ray tube, W-target, 2.5 mm Al, Vpeak = 25 kV. Michael Campbell

  15. Measures MTF @ various thresholds Michael Campbell

  16. NPS @ different thresholds NB. Dose changed from threshold to threshold to obtain good statistics Michael Campbell

  17. DQE @ different thresholds Michael Campbell

  18. Summary of measurements Michael Campbell

  19. Spectrum of X-ray source using energy window Raw sum of counts in all 64 000 pixels versus global threshold Threshold windows 1.4 keV 2.8 keV 4.2 keV Sn in bump bond 63% Ag in die attach glue Spectroscopic information – insight into environment Siefert FK-61-04x12 X-ray tube, W-target, 2.5 mm Al, Vpeak = 50 kV. Michael Campbell

  20. Image of a Swatch (16.1-19.6 keV) Michael Campbell

  21. Image of a Swatch (21.6-25.1 keV) Michael Campbell

  22. Image of a Swatch (27.1-31.4 keV) Michael Campbell

  23. Image of a Swatch (40.0-43.5 keV) Michael Campbell

  24. Comparison (16.1 – 19.6 keV) (21.6 – 25.1 keV) Michael Campbell

  25. Comparison (27.1 - 31.4 keV) (21.6 – 25.1 keV) Michael Campbell

  26. Comparison (27.1 - 31.4 keV) (40.0 - 43.5 keV) Michael Campbell

  27. Concluding remarks • The Medipix2 system offers clean particle imaging • MTF is typically 70% at pixel pitch. This can be enhanced by increasing threshold but at the expense of DQE • Energy window measurements provide insight into environment • Quantitative evaluation of the imaging properties using the energy window in preparation • Maybe the window should be used to exclude given energies! • And finally, a message for those who doubt the future of photon counting energy sensitive imaging systems….. Michael Campbell

  28. …the clock is ticking! < 1 frame/sec. Limited by DAQ software Michael Campbell

  29. Acknowledgements • Fellow members of the Medipix Consortium • www.cern.ch/medipix • Colleagues from Nikhef for Muros2 readout system • J. Visschers • H. Verkooijen • Colleagues the Naples group for Medisoft4.0 • P. Russo • G. Mettivier • M.C. Montesi Michael Campbell

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