title: Characterization of energy response for photon-counting detectors using x-ray fluorescence.
abstract: OBJECTIVE
  To investigate the feasibility of characterizing a Si strip photon-counting detector using x-ray fluorescence.
  
  
  METHODS
  X-ray fluorescence was generated by using a pencil beam from a tungsten anode x-ray tube with 2 mm Al filtration. Spectra were acquired at 90° from the primary beam direction with an energy-resolved photon-counting detector based on an edge illuminated Si strip detector. The distances from the source to target and the target to detector were approximately 19 and 11 cm, respectively. Four different materials, containing silver (Ag), iodine (I), barium (Ba), and gadolinium (Gd), were placed in small plastic containers with a diameter of approximately 0.7 cm for x-ray fluorescence measurements. Linear regression analysis was performed to derive the gain and offset values for the correlation between the measured fluorescence peak center and the known fluorescence energies. The energy resolutions and charge-sharing fractions were also obtained from analytical fittings of the recorded fluorescence spectra. An analytical model, which employed four parameters that can be determined from the fluorescence calibration, was used to estimate the detector response function.
  
  
  RESULTS
  Strong fluorescence signals of all four target materials were recorded with the investigated geometry for the Si strip detector. The average gain and offset of all pixels for detector energy calibration were determined to be 6.95 mV/keV and -66.33 mV, respectively. The detector's energy resolution remained at approximately 2.7 keV for low energies, and increased slightly at 45 keV. The average charge-sharing fraction was estimated to be 36% within the investigated energy range of 20-45 keV. The simulated detector output based on the proposed response function agreed well with the experimental measurement.
  
  
  CONCLUSIONS
  The performance of a spectral imaging system using energy-resolved photon-counting detectors is very dependent on the energy calibration of the detector. The proposed x-ray fluorescence technique offers an accurate and efficient way to calibrate the energy response of a photon-counting detector.
authors.affiliation: Department of Radiological Sciences, University of California, Irvine, California 92697.
authors.forename: Huanjun
authors.initials: H
authors.lastname: Ding
authors.affiliation: Department of Radiological Sciences, University of California, Irvine, California 92697.
authors.forename: Hyo-Min
authors.initials: HM
authors.lastname: Cho
authors.affiliation: DxRay, Inc., Northridgek, California 91324.
authors.forename: William C
authors.initials: WC
authors.lastname: Barber
authors.affiliation: DxRay, Inc., Northridgek, California 91324.
authors.forename: Jan S
authors.initials: JS
authors.lastname: Iwanczyk
authors.affiliation: Department of Radiological Sciences, University of California, Irvine, California 92697.
authors.forename: Sabee
authors.initials: S
authors.lastname: Molloi
mesh_terms: D055592:Biophysical Phenomena; D004867:Equipment Design; D006801:Humans; D008962:Models, Theoretical; D017785:Photons; D011874:Radiometry / Q000295:instrumentation* / Q000706:statistics & numerical data; D059629:Signal-To-Noise Ratio; D012825:Silicon; D013052:Spectrometry, X-Ray Emission / Q000295:instrumentation* / Q000706:statistics & numerical data; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data
chemical_list: D012825:Silicon