title: Dynamic contrast-enhanced computed tomography in metastatic nasopharyngeal carcinoma:  reproducibility analysis and observer variability of the distributed parameter model.
abstract: OBJECTIVE
  To determine the reproducibility and observer variability of distributed parameter analysis of dynamic contrast-enhanced computed tomography (DCE-CT) data in metastatic nasopharyngeal carcinoma, and to compare 2 approaches of region-of-interest (ROI) analyses.
  
  
  METHODS
  Following ethical approval and informed consent, 17 patients with nasopharyngeal carcinoma underwent paired DCE-CT examinations on a 64-detector scanner, measuring tumor blood flow (F, mL/100 mL/min), permeability surface area product (PS, mL/100 mL/min), fractional intravascular blood volume (v1, mL/100 mL), and fractional extracellular-extravascular volume (v2, mL/100 mL). Tumor parameters were derived by fitting (i) the ROI-averaged concentration-time curve, and (ii) the median value of parameters from voxel-level concentration-time curves. Measurement reproducibility and inter- and intraobserver variability were estimated using Bland-Altman statistics.
  
  
  RESULTS
  Mean F, PS, v1, and v2 are 44.9, 20.4, 7.1, and 34.1 for ROI analysis, and 49.0, 18.7, 6.7, and 34.0 for voxel analysis, respectively. Within-subject coefficients of variation are 38.8%, 49.5%, 54.2%, and 35.9% for ROI analysis, and 15.0%, 35.1%, 33.0%, and 21.0% for voxel analysis, respectively. Repeatability coefficients are 48.2, 28.0, 10.7, and 33.9 for ROI analysis, and 20.3, 18.2, 6.1 and 19.8 for voxel analysis, respectively. Intra- and interobserver correlation coefficient ranged from 0.94 to 0.97 and 0.90 to 0.95 for voxel analysis, and 0.73 to 0.87 and 0.72 to 0.94 for ROI analysis, respectively.
  
  
  CONCLUSIONS
  Measurements of F and v2 appear more reproducible than PS and v1. Voxel-level analysis improves both reproducibility and observer variability compared with ROI-averaged analysis and may retain information about tumor spatial heterogeneity.
authors.affiliation: Department of Medical Oncology, National Cancer Centre Singapore, Singapore, Republic of Singapore. ng.q.s@nccs.com.sg
authors.forename: Quan-Sing
authors.initials: QS
authors.lastname: Ng
authors.forename: Choon Hua
authors.initials: CH
authors.lastname: Thng
authors.forename: Wan Teck
authors.initials: WT
authors.lastname: Lim
authors.forename: Septian
authors.initials: S
authors.lastname: Hartono
authors.forename: Yee Liang
authors.initials: YL
authors.lastname: Thian
authors.forename: Puor Sherng
authors.initials: PS
authors.lastname: Lee
authors.forename: Daniel Shao-Weng
authors.initials: DS
authors.lastname: Tan
authors.forename: Eng Huat
authors.initials: EH
authors.lastname: Tan
authors.forename: Tong San
authors.initials: TS
authors.lastname: Koh
mesh_terms: D000328:Adult; D002277:Carcinoma / Q000000981:diagnostic imaging* / Q000556:secondary* / Q000628:therapy; D003287:Contrast Media; D005260:Female; D006801:Humans; D007472:Iohexol; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging* / Q000556:secondary* / Q000628:therapy; D015588:Observer Variation; D055420:Perfusion Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome
chemical_list: D003287:Contrast Media; D007472:Iohexol