Ventilation/perfusion scintigraphy.

V/Q imaging is often very useful in evaluating patients in whom a PE is suspected. A normal scan result can be used to exclude embolism and a high likelihood ratio scan can be used to make the diagnosis of PE. Most patients with PE do not have high likelihood ratio scans; therefore, it is important to pursue this diagnosis in patients with intermediate likelihood ratio scans and in the appropriate clinical setting for patients with the low likelihood ratio scans. In patients with parenchymal chest x-ray abnormalities who are likely to fall into the intermediate category, it can be more appropriate to use CT angiography instead of V/Q scintigraphy. This strategy probably increases the fraction of scans with high diagnostic utility.