Objective analysis of tomographic ventilation-perfusion scintigraphy in pulmonary embolism. 
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.  To determine the diagnostic accuracy of objective SPECT analysis in PE.  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.  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.  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.