A dynamic attenuator improves spectral imaging with energy-discriminating, photon counting detectors

Scott S. Hsieh, Norbert J. Pelc

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Energy-discriminating, photon counting (EDPC) detectors have high potential in spectral imaging applications but exhibit degraded performance when the incident count rate approaches or exceeds the characteristic count rate of the detector. In order to reduce the requirements on the detector, we explore the strategy of modulating the X-ray flux field using a recently proposed dynamic, piecewise-linear attenuator. A previous paper studied this modulation for photon counting detectors but did not explore the impact on spectral applications. In this work, we modeled detection with a bipolar triangular pulse shape (Taguchi , 2011) and estimated the Cramer-Rao lower bound (CRLB) of the variance of material selective and equivalent monoenergetic images, assuming deterministic errors at high flux could be corrected. We compared different materials for the dynamic attenuator and found that rare earth elements, such as erbium, outperformed previously proposed materials such as iron in spectral imaging. The redistribution of flux reduces the variance or dose, consistent with previous studies on benefits with conventional detectors. Numerical simulations based on DICOM datasets were used to assess the impact of the dynamic attenuator for detectors with several different characteristic count rates. The dynamic attenuator reduced the peak incident count rate by a factor of 4 in the thorax and 44 in the pelvis, and a 10 Mcps/mm2 EDPC detector with dynamic attenuator provided generally superior image quality to a 100 Mcps/mm2 detector with reference bowtie filter for the same dose. The improvement is more pronounced in the material images.

Original languageEnglish (US)
Article number6910270
Pages (from-to)729-739
Number of pages11
JournalIEEE transactions on medical imaging
Issue number3
StatePublished - Mar 1 2015


  • Dose reduction
  • dynamic bowtie filter
  • fluence modulation
  • photon counting detectors

ASJC Scopus subject areas

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


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