In what order are imaging studies obtained in the workup of patients with suspected acute pulmonary embolism?
The first imaging study performed in a patient with suspected pulmonary embolism is typically a chest radiograph. This will often reveal as well as exclude many underlying etiologies and is also necessary for the adequate evaluation of a V/Q scan. The next imaging study performed depends on a number of variables including the current diagnostic evaluation protocols regionally determined by individual hospitals but, more important, on whether the chest radiograph is normal or abnormal. Many hospitals now utilize contrast-enhanced computed tomography (CT) tailored toward evaluation of the pulmonary arterial tree to evaluate for presence of pulmonary embolism as well as for other cardiopulmonary disease conditions. In patients with significant abnormalities seen on chest radiography, it is more likely that a V/Q scan will result in an indeterminate test result and not provide additional diagnostic information. Therefore, only patients with relatively normal chest radiographs generally proceed to V/Q scanning. If a CT and/or a V/Q scan are equivocal for detection of pulmonary embolism, then conventional pulmonary angiography may be performed. Lower extremity ultrasonography (US) may also be used to evaluate for the presence of deep venous thrombosis (DVT).