title: Incremental diagnostic quality gain of CTA over V/Q scan in the assessment of pulmonary embolism by means of a Wells score Bayesian model: results from the ACDC collaboration.
abstract: OBJECTIVE
  Our objective was to evaluate the diagnostic value of computed tomography angiography (CTA) and ventilation perfusion (V/Q) scan in the assessment of pulmonary embolism (PE) by means of a Bayesian statistical model.
  
  
  METHODS
  Wells criteria defined pretest probability. Sensitivity and specificity of CTA and V/Q scan for PE were derived from pooled meta-analysis data. Likelihood ratios calculated for CTA and V/Q were inserted in the nomogram. Absolute (ADG) and relative diagnostic gains (RDG) were analyzed comparing post- and pretest probability. Comparative gain difference was calculated for CTA ADG over V/Q scan integrating ANOVA p value set at 0.05.
  
  
  RESULTS
  The sensitivity for CT was 86.0% (95% CI: 80.2%, 92.1%) and specificity of 93.7% (95% CI: 91.1%, 96.3%). The V/Q scan yielded a sensitivity of 96% (95% CI: 95%, 97%) and a specificity of 97% (95% CI: 96%, 98%). Bayes nomogram results for CTA were low risk and yielded a posttest probability of 71.1%, an ADG of 56.1%, and an RDG of 374%, moderate-risk posttest probability was 85.1%, an ADG of 56.1%, and an RDG of 193.4%, and high-risk posttest probability was 95.2%, an ADG of 36.2%, and an RDG of 61.35%. The comparative gain difference for low-risk population was 46.1%; in moderate-risk 41.6%; and in high-risk a 22.1% superiority. ANOVA analysis for LR+ and LR- showed no significant difference (p = 0.8745, p = 0.9841 respectively).
  
  
  CONCLUSIONS
  This Bayesian model demonstrated a superiority of CTA when compared to V/Q scan for the diagnosis of pulmonary embolism. Low-risk patients are recognized to have a superior overall comparative gain favoring CTA.
authors.affiliation: Universitat de Barcelona, Barcelona, Spain. lailacochon@hotmail.com.
authors.forename: Laila
authors.initials: L
authors.lastname: Cochon
authors.affiliation: University of Miami Miller School of Medicine, Miami, FL, USA.
authors.forename: Kaitlin
authors.initials: K
authors.lastname: McIntyre
authors.affiliation: Medical Intensive Care Unit, Hospital Clínic de Barcelona, Universitat de Barcelona, Barcelona, Spain.
authors.forename: José M
authors.initials: JM
authors.lastname: Nicolás
authors.affiliation: Jackson Memorial Hospital, Miami, FL, USA.
authors.forename: Amado Alejandro
authors.initials: AA
authors.lastname: Baez
mesh_terms: D001499:Bayes Theorem; D000072226:Computed Tomography Angiography; D006801:Humans; D064847:Multimodal Imaging; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging*; D012680:Sensitivity and Specificity; D014692:Ventilation-Perfusion Ratio
keywords: Bayesian model; CT angiography; Pulmonary embolism; V/Q scan