Pulmonary arteries are opacified with contrast. This evaluates for intra-arterial thrombi within the pulmonary arteries, which are seen as filling defects. The disadvantages of this examination are its expense and invasiveness. Ultrasound on a basic level simply evaluates for clot within veins as seen sonographically such that the veins will not compress. Normal veins collapse when pushed by the transducer.
Arteries are more difficult to compress due to their muscular walls.
Doppler also assists in this examination. It has a low complication rate but is uncomfortable, more expensive, and is still more invasive than venous ultrasound. First pass contrast enhanced pulmonary MR angiography is also being evaluated for the diagnosis of pulmonary embolism. These techniques have yet to gain wides acceptance. However, more recently CT and MRI have been used to evaluate for arterial disease.