title: Objective analysis of tomographic ventilation-perfusion scintigraphy in pulmonary embolism.
abstract: BACKGROUND
  Ventilation-perfusion scintigraphy is highly sensitive for pulmonary embolism (PE), but its clinical usefulness is limited by its nondiagnostic rate. Objective analysis of single photon emission computed tomography (SPECT) three-dimensional scintigraphy may improve its diagnostic performance compared with subjective interpretation.
  
  
  OBJECTIVE
  To determine the diagnostic accuracy of objective SPECT analysis in PE.
  
  
  METHODS
  We determined the ventilation/perfusion (V(.)/Q(.)) relationship using SPECT scintigraphy in a retrospective cohort of 73 patients. Measures of V(.)/Q(.) heterogeneity (logSD(Q(.)), logSD(V(.)), logSD(VQR)), including a novel parameter, the weighted median V(.)/Q(.) value, were calculated. Using receiver operating characteristic (ROC) analysis, each parameter's diagnostic accuracy was determined. The weighted median V(.)/Q(.) value was then assessed prospectively in a second cohort of 50 patients.
  
  
  RESULTS
  In cohort 1, all parameters of V(.)/Q(.) heterogeneity were higher in patients with PE (p < 0.002). The weighted median V(.)/Q(.) had the highest area under the ROC curve (0.93; 95% confidence interval, 0.87-0.98). When applied to the prospective cohort, the area under the ROC curve was 0.87 (95% confidence interval, 0.75-0.99), with diagnostic cutoff values having negative and positive predictive values of 96 and 83%, respectively. In the retrospective and prospective cohorts, 82 and 73% of initially reported intermediate or low probability scans had diagnostic weighted median V(.)/Q(.) values, with 90 and 100% accuracy, respectively.
  
  
  CONCLUSIONS
  Objective analysis of SPECT scintigraphy has a high diagnostic accuracy in patients with suspected PE. Objective analysis has the potential to reduce the number of nondiagnostic scan results, and may be useful for quantifying V(.)/Q(.) mismatch in other pulmonary disorders.
authors.affiliation: Department of Respiratory Medicine, Royal North Shore Hospital, Pacific Highway, St. Leonards 2065, Australia. bharris@med.usyd.edu.au
authors.forename: Benjamin
authors.initials: B
authors.lastname: Harris
authors.forename: Dale
authors.initials: D
authors.lastname: Bailey
authors.forename: Susan
authors.initials: S
authors.lastname: Miles
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Bailey
authors.forename: Kerry
authors.initials: K
authors.lastname: Rogers
authors.forename: Paul
authors.initials: P
authors.lastname: Roach
authors.forename: Paul
authors.initials: P
authors.lastname: Thomas
authors.forename: Michael
authors.initials: M
authors.lastname: Hensley
authors.forename: Gregory G
authors.initials: GG
authors.lastname: King
mesh_terms: D000368:Aged; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D012372:ROC Curve; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012720:Severity of Illness Index; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014692:Ventilation-Perfusion Ratio / Q000502:physiology