title: Characteristic performance evaluation of a photon counting Si strip detector for low dose spectral breast CT imaging.
abstract: OBJECTIVE
  The possible clinical applications which can be performed using a newly developed detector depend on the detector's characteristic performance in a number of metrics including the dynamic range, resolution, uniformity, and stability. The authors have evaluated a prototype energy resolved fast photon counting x-ray detector based on a silicon (Si) strip sensor used in an edge-on geometry with an application specific integrated circuit to record the number of x-rays and their energies at high flux and fast frame rates. The investigated detector was integrated with a dedicated breast spectral computed tomography (CT) system to make use of the detector's high spatial and energy resolution and low noise performance under conditions suitable for clinical breast imaging. The aim of this article is to investigate the intrinsic characteristics of the detector, in terms of maximum output count rate, spatial and energy resolution, and noise performance of the imaging system.
  
  
  METHODS
  The maximum output count rate was obtained with a 50 W x-ray tube with a maximum continuous output of 50 kVp at 1.0 mA. A109Cd source, with a characteristic x-ray peak at 22 keV from Ag, was used to measure the energy resolution of the detector. The axial plane modulation transfer function (MTF) was measured using a 67 μm diameter tungsten wire. The two-dimensional (2D) noise power spectrum (NPS) was measured using flat field images and noise equivalent quanta (NEQ) were calculated using the MTF and NPS results. The image quality parameters were studied as a function of various radiation doses and reconstruction filters. The one-dimensional (1D) NPS was used to investigate the effect of electronic noise elimination by varying the minimum energy threshold.
  
  
  RESULTS
  A maximum output count rate of 100 million counts per second per square millimeter (cps/mm2) has been obtained (1 million cps per 100×100 μm pixel). The electrical noise floor was less than 4 keV. The energy resolution measured with the 22 keV photons from a 109Cd source was less than 9%. A reduction of image noise was shown in all the spatial frequencies in 1D NPS as a result of the elimination of the electronic noise. The spatial resolution was measured just above 5 line pairs per mm (lp/mm) where 10% of MTF corresponded to 5.4 mm(-1). The 2D NPS and NEQ shows a low noise floor and a linear dependence on dose. The reconstruction filter choice affected both of the MTF and NPS results, but had a weak effect on the NEQ.
  
  
  CONCLUSIONS
  The prototype energy resolved photon counting Si strip detector can offer superior imaging performance for dedicated breast CT as compared to a conventional energy-integrating detector due to its high output count rate, high spatial and energy resolution, and low noise characteristics, which are essential characteristics for spectral breast CT imaging.
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., Northridge, California 91324.
authors.forename: William C
authors.initials: WC
authors.lastname: Barber
authors.affiliation: Department of Radiological Sciences, University of California, Irvine, California 92697.
authors.forename: Huanjun
authors.initials: H
authors.lastname: Ding
authors.affiliation: DxRay Inc., Northridge, 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: D002138:Calibration; D008327:Mammography / Q000295:instrumentation* / Q000379:methods; D017785:Photons; D012825:Silicon; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods; D014965:X-Rays
chemical_list: D012825:Silicon