Again, not an ideal situation. HCT is designed to accomplish large volume acquisitions in a breathhold, limiting motion artifact related to respiration, heart activity, etc. This technology is expensive and its other applications are limited. As a result, electron-beam CT has not flourished in practice. It is often argued that helical CT has limited accuracy for subsegmental emboli.
Subsegmental emboli are of controversial significance.
A growing concensus suggests they may have some significance in those with chronic cardiopulmonary disease. Pulmonary vessels that have a relatively horizontal traverse, such as the lateral segment, right middle lobe pulmonary artery, can occasionally produce a diagnostic challenge. Peribronchial lymphatic tissue often at the take-offs of the upper lobe vessels, must not be mistaken for clot. Typically, it will not narrow the vessel and is interposed between the vessel and bronchus. This often results from motion or insufficient vascular opacification.