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Objective Analysis of Tomographic Ventilation–Perfusion Scintigraphy in Pulmonary Embolism

¹ Department of Respiratory Medicine, Royal North Shore Hospital, Sydney, Australia; ² Northern Clinical School, Faculty of Medicine, University of Sydney, Sydney, Australia; ³ The Woolcock Institute of Medical Research, Sydney, Australia; ⁴ Department of Nuclear Medicine, Royal North Shore Hospital, Sydney, Australia; ⁵ School of Medical Radiation Sciences, University of Sydney, Sydney, Australia; Departments of ⁶ Respiratory and Sleep Medicine and ⁷ Nuclear Medicine, John Hunter Hospital, Newcastle, Australia; and ⁸ School of Medicine and Public Health, University of Newcastle, Newcastle, Australia

Correspondence and requests for reprints should be addressed to Benjamin Harris, M.B. B.S., Department of Respiratory Medicine, Royal North Shore Hospital, Pacific Highway, St. Leonards 2065, Australia. E-mail: bharris{at}med.usyd.edu.au

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 (/) relationship using SPECT scintigraphy in a retrospective cohort of 73 patients. Measures of / heterogeneity (logSD_Q, logSD_V, logSD_VQR), including a novel parameter, the weighted median / value, were calculated. Using receiver operating characteristic (ROC) analysis, each parameter's diagnostic accuracy was determined. The weighted median / value was then assessed prospectively in a second cohort of 50 patients.

Measurements and Main Results: In cohort 1, all parameters of / heterogeneity were higher in patients with PE (p < 0.002). The weighted median / 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 / 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 / mismatch in other pulmonary disorders.

Key Words: tomography, emission-computed, single-photon • radionuclide imaging • ventilation–perfusion ratio • pulmonary embolism • image processing, computer-assisted

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject No work has been done to date on the objective analysis of ventilation–perfusion single photon emission computed tomography (SPECT) scintigraphy to investigate ventilation/perfusion (/) relationships in patients with potential pulmonary embolism. What This Study Adds to the Field Objective analysis of SPECT scintigraphy has a high diagnostic accuracy in patients with suspected pulmonary embolism.

 

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