title: [Evaluation method of CT number linearity].
abstract: OBJECTIVE
  To explore the method for computed tomography (CT) number linearity evaluation.
  
  
  METHODS
  The model CTP401 of Catphan500 phantom was adopted to test 43 sets of CT scanners under the same scanning conditions. 1- and 2-order curve fitting of the testing results of each scanner were performed, with the bending of the 2-order fitted curve defined as the degree of CT number non-linearity and the slope of the linear fitting as contrast scale. The 2-norms of the fitting coefficients were calculated for the purpose of fitting quality evaluation. MATLAB 6.1 was employed for programming.
  
  
  RESULTS
  The 2-norm of the fitting coefficients of the 2-order fitting curve was approximately 1/10 of that of corresponding linear fitting, indicating that 2-order fitting accorded better to the parent population distribution pattern. The degree of the non-linearity was manifested by the bending of the 2-order fitting curve that increased monotonously with the 2-norm of the corresponding linear fitting.
  
  
  CONCLUSIONS
  It is statistically valid to define CT number non-linearity and contrast scale on the basis of 1 and 2-order fittings of the testing results, which well serves the purpose of quantitative analysis.
authors.affiliation: Department of Biomedical Engineering, First Military Medical University, Guangzhou 510515, China. yangkch@fimmu.edu.cn
authors.forename: Ke-Cheng
authors.initials: KC
authors.lastname: Yang
authors.forename: Yin-Qun
authors.initials: YQ
authors.lastname: Lin
authors.forename: Xiao-E
authors.initials: XE
authors.lastname: Yu
authors.forename: Guang-Wen
authors.initials: GW
authors.lastname: Lu
authors.forename: Mu-Yan
authors.initials: MY
authors.lastname: Lin
mesh_terms: D000465:Algorithms; D013223:Statistics as Topic / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000592:standards