Radiological (scintigraphic) evaluation of patients with suspected pulmonar thromboembolism

The optimal strategy for diagnostic evaluation of patients with suspected pulmonary thromboembolism (PE) is subject of controversial and often conflicting opinions. If untreated, as many as 30% of patients with PE may die. Conversely, anticoagulant therapy significantly decreases mortality from PE, but bleeding complications occur. Underdiagnosis may result in a preventable death, and overdiagnosis may lead to significant hemorrhage from unnecessary anticoagulant therapy. This article outlines a practical guide for the use of pulmonary ventilation-perfusion (V-P) scintigraphy in patients with suspected PE. Perfusion imaging involves the intravenous injection of radiolabeled particles ranging from 10 to 60 μm in diameter (technetium Tc 99m macroaggregated albumin or technetium Tc 99m serum albumin microspheres); these particles are trapped in the capillaries and precapillary arterioles of the lung. The radiolabeled particles are distributed to the lungs in proportion to regional pulmonary blood flow. The correspondence of perfusion defects to bronchopulmonary segments is best appreciated in the posterior oblique views