title: Performance characterization of a MVCT scanner using multislice thick, segmented cadmium tungstate-photodiode detectors.
abstract: OBJECTIVE
  Megavoltage computed tomography (MVCT) and megavoltage cone beam computed tomography (MVCBCT) can be used for visualizing anatomical structures prior to radiation therapy treatments to assist in patient setup and target localization. These systems are less susceptible to metal artifacts and provide better CT number linearity than conventional CT scanners. However, their contrast is limited by the properties of the megavoltage photons and the low detective quantum efficiency (DQE) of flat panel detector systems currently available. By using higher DQE, thick, segmented cadmium tungstate detectors, the authors can improve the low contrast detectability of a MVCT system. This in turn would permit greater soft tissue visualization for a given radiation dose, allowing MVCT to be used in more clinical situations.
  
  
  METHODS
  This article describes the evaluation of our prototype system that uses thick, segmented detectors. In order to create images using a dose that would be acceptable for day to day patient imaging, the authors evaluated their system using the low intensity bremsstrahlung component of a 6 MeV electron beam. The system was evaluated for its uniformity, high contrast resolution, low contrast detectability, signal to noise ratio, contrast to noise ratio, and CT number linearity.
  
  
  RESULTS
  The prototype system was found to have a high contrast spatial resolution of about 5 line pairs per cm, and to be able to visualize a 15 mm 1.5% contrast target with 2 cGy of radiation dose delivered. SNR2 vs radiation dose and mean pixel value vs electron density curves were linear.
  
  
  CONCLUSIONS
  This prototype system shows a large improvement in low contrast detectability over current MVCBCT systems.
authors.affiliation: Department of Physics, University of Alberta, Edmonton, Alberta T6E 2E1, Canada. pkirvan@ualberta.ca
authors.forename: P F
authors.initials: PF
authors.lastname: Kirvan
authors.forename: T T
authors.initials: TT
authors.lastname: Monajemi
authors.forename: B G
authors.initials: BG
authors.lastname: Fallone
authors.forename: S
authors.initials: S
authors.lastname: Rathee
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D010865:Pilot Projects; D011856:Radiographic Image Enhancement / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012666:Semiconductors; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*; D014159:Transducers; D017973:Tungsten Compounds / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D017973:Tungsten Compounds; C052547:cadmium tungsten oxide