the first examination should always be a CXR! The chest x-ray aids in the interpretation of the lung scan. It also identifies non-embolic conditions superficially mimicking those of pulmonary embolus such as pneumonia, CHF, or pneumothorax. After the CXR is completed, diagnosis of PE is addressed specifically by either a NM lung V/Q scan or a chest CT with pulmonary embolus protocol. Most of the time the imaging evaluation ends at this point. Pulmonary arteriography is suggested only when there is a medical contraindication to anticoagulation that makes absolute diagnosis of PE a necessity or it is technically impossible to perform an adequate V/Q scan or CT PE angiogram. An US of the legs (or occasionally an arm with a central line or other predisposing factor) may be considered concurrently to evaluate for DVT.