Use of depth information from in-depth photon counting detectors for x-ray spectral imaging: A preliminary simulation study

Yuan Yao, Hans Bornefalk, Scott S. Hsieh, Mats Danielsson, Norbert J. Pelc

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

2 Scopus citations


Purpose: Photon counting x-ray detectors (PCXD) may improve dose-efficiency but are hampered by limited count rate. They generally have imperfect energy response. Multi-layer ("in-depth") detectors have been proposed to enable higher count rates but the potential benefit of the depth information has not been explored. We conducted a simulation study to compare in-depth detectors against single layer detectors composed of common materials. Both photon counting and energy integrating modes were studied. Methods: Polyenergetic transmissions were simulated through 25cm of water and 1cm of calcium. For PCXD composed of Si, GaAs or CdTe a 120kVp spectrum was used. For energy integrating x-ray detectors (EIXD) made from GaAs, CdTe or CsI, spectral imaging was done using 80 and 140kVp and matched dose. Semi-ideal and phenomenological energy response models were used. To compare these detectors, we computed the Cramér-Rao lower bound (CRLB) of the variance of basis material estimates. Results: For PCXDs with perfect energy response, depth data provides no additional information. For PCXDs with imperfect energy response and for EIXDs the improvement can be significant. E.g., for a CdTe PCXD with realistic energy response, depth information can reduce the variance by 50%. The improvement depends on the x-ray spectrum. For a semi-ideal Si detector and a narrow x-ray spectrum the depth information has minimal advantage. For EIXD, the in-depth detector has consistent variance reduction (15% and 17%19% for water and calcium, respectively). Conclusions: Depth information is beneficial to spectral imaging for both PCXD and EIXD. The improvement depends critically on the detector energy response.

Original languageEnglish (US)
Title of host publicationMedical Imaging 2014
Subtitle of host publicationPhysics of Medical Imaging
ISBN (Print)9780819498267
StatePublished - 2014
EventMedical Imaging 2014: Physics of Medical Imaging - San Diego, CA, United States
Duration: Feb 17 2014Feb 20 2014

Publication series

NameProgress in Biomedical Optics and Imaging - Proceedings of SPIE
ISSN (Print)1605-7422


OtherMedical Imaging 2014: Physics of Medical Imaging
Country/TerritoryUnited States
CitySan Diego, CA


  • CRLB
  • Energy Response Function
  • Material Decomposition
  • Photon-counting Detector
  • Spectral CT

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Atomic and Molecular Physics, and Optics
  • Radiology Nuclear Medicine and imaging


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