Effect of spectral degradation and spatio-energy correlation in x-ray pcd for imaging

Paurakh L. Rajbhandary, Scott S. Hsieh, Norbert J. Pelc

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Charge sharing, scatter, and fluorescence events in a photon counting detector can result in counting of a single incident photon in multiple neighboring pixels, each at a fraction of the true energy. This causes energy distortion and correlation of data across energy bins in neighboring pixels (spatio-energy correlation), with the severity depending on the detector pixel size and detector material. If a 'macro-pixel' is formed by combining the counts from multiple adjacent small pixels, it will exhibit correlations across its energy bins. Understanding these effects can be crucial for detector design and for model-based imaging applications. This paper investigates the impact of these effects in basis material and effective monoenergetic estimates using the Cramér-Rao Lower Bound. To do so, we derive a correlation model for the multi-counting events. CdTe detectors with grids of pixels with side length of 250μm , 500μm , and 1 mm were compared, with binning of 4×4 , 2×2 , and 1×1 pixels, respectively, to keep the same net 1 mm 2 aperture constant. The same flux was applied to each. The mean and covariance matrix of measured photon counts were derived analytically using spatio-energy response functions precomputed from Monte Carlo simulations. Our results show that a 1 mm 2 macro-pixel with 250× 250 mu;m 2 sub-pixels shows 35% higher standard deviation than a single 1 mm 2 pixel for material-specific imaging, while the penalty for effective monoenergetic imaging is <10% compared with a single 1 mm 2 pixel. Potential benefits of sub-pixels (higher spatial resolution and lower pulse pile-up effects) are important but were not investigated here.

Original languageEnglish (US)
Article number8356096
Pages (from-to)1910-1919
Number of pages10
JournalIEEE transactions on medical imaging
Issue number8
StatePublished - Aug 2018


  • Charge Sharing
  • K-Fluorescence Escape
  • Material Decomposition
  • Photon Counting X-Ray Detector
  • Spatio-Energetic Correlation
  • Spectral CT

ASJC Scopus subject areas

  • Software
  • Radiological and Ultrasound Technology
  • Computer Science Applications
  • Electrical and Electronic Engineering


Dive into the research topics of 'Effect of spectral degradation and spatio-energy correlation in x-ray pcd for imaging'. Together they form a unique fingerprint.

Cite this