title: Detector response function of an energy-resolved CdTe single photon counting detector.
abstract: BACKGROUND
  While spectral CT using single photon counting detector has shown a number of advantages in diagnostic imaging, knowledge of the detector response function of an energy-resolved detector is needed to correct the signal bias and reconstruct the image more accurately.
  
  
  OBJECTIVE
  The objective of this paper is to study the photo counting detector response function using laboratory sources, and investigate the signal bias correction method.
  
  
  METHODS
  Our approach is to model the detector response function over the entire diagnostic energy range (20 keV <E< 140 keV) using a semi-analytical method with 12 parameters. The model includes a primary photo peak, an exponential tail, and four escape peaks. Four radioactive isotopes including Cdmium-109, Barium-133, Americium-241 and Cobalt-57 are used to generate the detector response function at six photon energies. The 12 parameters are obtained by non-linear least-square fitting with the measured detector response functions at the six energies. The correlations of the 12 parameters with energy are also investigated with the measured data.
  
  
  RESULTS
  The analytical model generally describes the detector response function and is in good agreement with the measured data. The trend lines of the 12 parameters indicate higher energies tend to cause grater spectrum distortion. The spectrum distortion caused by the detector response function on spectral CT reconstruction is analyzed theoretically, and a solution to correct this spectrum distortion is also proposed.
  
  
  CONCLUSIONS
  In spectral and fluorescence CT, the spectrum distortion caused by detector response function poses a problem and cannot be ignored in any quantitative analysis. The detector response function of a CdTe detector can be obtained by a semi-analytical method.
authors.affiliation: Nuclear Engineering, Missouri University of Science and Technology, Rolla, MO, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.affiliation: Nuclear Engineering, Missouri University of Science and Technology, Rolla, MO, USA.
authors.forename: Hyoung Koo
authors.initials: HK
authors.lastname: Lee
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D002138:Calibration; D008962:Models, Theoretical; D013691:Tellurium / Q000737:chemistry*; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation* / Q000379:methods*
chemical_list: D019187:Cadmium Compounds; D013691:Tellurium; C028337:cadmium telluride
keywords: Photon counting; detector response function; spectrum distortion