Pulmonary nuclear medicine evaluation of thromboembolic disease

PE is a complication of underlying venous thrombosis and most often arises from the deep veins of the lower extremities. The thromboembolic event is difficult to diagnose clinically and carries significant morbidity and mortality. Treatment with anticoagulation also has risks. Thus accurate diagnosis is important. A normal perfusion lung scan excludes major pulmonary emboli. Lung perfusion scintigraphy provides high sensitivity for interrupted blood flow but lacks specificity for embolic vascular occlusion. Ventilation scintigraphy is sensitive for obstructive pulmonary disease and improves specificity for PE when combined with the perfusion scan. Several retrospective studies have established probability levels for PE on the basis of certain ventilation, perfusion, and chest x-ray patterns. These results have high positive and negative predictive value and directly affect patient management. The first large prospective study on PE has just been completed. The results of this study should more clearly define the role for ventilation-perfusion scintigraphy in PE.