Scintigraphy-ventilatio/perfusion scanning and imaging of the embolus

Summary

Purpose: This is a review of data on ventilation/perfusion (V/Q) imaging obtained in the collaborative study, Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). Special emphasis is given to data obtained subsequent to the main PIOPED publication. New criteria for the interpretation of V/Q scans are based on data obtained by retrospective evaluation of the data from PIOPED.

Background: PIOPED was a prospective randomized double blind investigation of the validity of V/Q scans, based on an angiographic diagnosis of acute pulmonary embolism (PE) in 251 patients and an angiographic exclusion of PE in 480 patients and based on follow-up of patients with normal V/Q scans who did not undergo angiography.

Results: The original PIOPED criteria for interpretation of V/Q scans are reviewed. The positive predictive value of V/Q scans based on these criteria is shown. Clinical assessment in combination with objective readings of V/Q scans is evaluated. The positive predictive value of V/Q scans is assessed according to the complexity of associated disease. The validity of the perfusion scan alone is evaluated. Revised criteria for the interpretation of V/Q scans are described. Criteria for a very low probability interpretation are proposed. The importance of small perfusion defects is described. The diagnostic value of matched ventilation, perfusion and chest radiographic abnormalities is described. The concept of segmental equivalent perfusion defects is assessed. The concept of a mismatched vascular defect, whether moderate or large size, is described. An interpretation of V/Q scans based on the presence of a mismatched perfusion defect in patients stratified according to prior cardiopulmonary disease is described.

Conclusion: Retrospective analysis of the data from PIOPED has permitted an extensive assessment of the diagnostic validity of V/Q scans since the original PIOPED publication. New criteria for interpretation of V/Q scans have been proposed.