Scintigraphic evaluation of pulmonary embolism

Pulmonary embolism (PE) is difficult to diagnose. The clinical signs and symptoms of the disorder are nonspecific, and the results of laboratory tests are undependable. Accordingly, imaging studies have played a major role in evaluation of patients with suspected PE. Chest radiography is an essential part of this imaging evaluation, but is neither sensitive nor specific, per se. The radiograph is used primarily to provide a regional comparison for ventilation-perfusion (V-P) scintigraphy. V-P scintigraphy typically is the pivotal noninvasive approach to diagnosis of PE. Multi-view perfusion scintigraphy is a sensitive means for detecting the multiple, wedge-shaped defects characteristic of PE. The perfusion scan's inherent nonspecificity is improved by the ventilation study, which reveals abnormalities of ventilation that account for perfusion defects not caused by PE. Multi-view ventilation imaging with either the xenon gases, Kr-81m or radioaerosols is useful for comparison with perfusion scans. When performed properly and interpreted within the guidelines of current diagnostic schemes for scintigraphy, V-P studies provide approximately 90% reliability for the diagnosis of PE. When used alone or in conjunction with noninvasive studies of deep venous thrombosis, they provide an excellent basis for selection of certain patients for pulmonary angiography, and for other decisions about the clinical management of patients with suspected PE.