Objective analysis of tomographic ventilation-perfusion scintigraphy in pulmonary embolism

Rationale: 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. Objectives: 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. Measurements and Main 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.