Evaluation of a photon counting Medipix3RX CZT spectral x-ray detector

Steven M. Jorgensen, Andrew J. Vercnocke, David S. Rundle, Philip H. Butler, Cynthia H. McCollough, Erik L. Ritman

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Scopus citations


We assessed the performance of a cadmium zinc telluride (CZT)-based Medipix3RX x-ray detector as a candidate for micro-computed tomography (micro-CT) imaging. This technology was developed at CERN for the Large Hadron Collider. It features an array of 128 by 128, 110 micrometer square pixels, each with eight simultaneous threshold counters, five of which utilize real-time charge summing, significantly reducing the charge sharing between contiguous pixels. Pixel response curves were created by imaging a range of x-ray intensities by varying x-ray tube current and by varying the exposure time with fixed x-ray current. Photon energy-related assessments were made by flooding the detector with the tin foil filtered emission of an I-125 radioisotope brachytherapy seed and sweeping the energy threshold of each of the four charge-summed counters of each pixel in 1 keV steps. Long term stability assessments were made by repeating exposures over the course of one hour. The high properly-functioning pixel yield (99%), long term stability (linear regression of whole-chip response over one hour of acquisitions: y = -0.0038x + 2284; standard deviation: 3.7 counts) and energy resolution (2.5 keV FWHM (single pixel), 3.7 keV FWHM across the full image) make this device suitable for spectral micro-CT. The charge summing performance effectively reduced the measurement corruption caused by charge sharing which, when unaccounted for, shifts the photon energy assignment to lower energies, degrading both count and energy accuracy. Effective charge summing greatly improves the potential for calibrated, energy-specific material decomposition and K edge difference imaging approaches.

Original languageEnglish (US)
Title of host publicationRadiation Detectors
Subtitle of host publicationSystems and Applications XVII
EditorsGary P. Grim, Lars R. Furenlid, H. Bradford Barber
ISBN (Electronic)9781510603295
StatePublished - 2016
EventRadiation Detectors: Systems and Applications XVII - San Diego, United States
Duration: Aug 31 2016Sep 1 2016

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherRadiation Detectors: Systems and Applications XVII
Country/TerritoryUnited States
CitySan Diego


  • CZT-based spectral micro-CT
  • Medipix
  • charge sharing
  • photon counting
  • x-ray microtomography

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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