If it is necessary to evaluate an image that is not labeled for position, how does one determine which position the patient was in when the film was taken?

There are two ways to tell which position the patient was in when the exam was done:

1. Evaluate which structures contain air. If ventral structures (e.g., the antrum of the stomach) contain air, the patient was probably supine when the exam was done. If the gas is in the fundus, the exam was done with the patient upright.

2. Look for horizontal interfaces consisting of air above and fluid below (i.e., air-fluid levels). These interfaces indicate that the exam was done with the patient either upright or in the decubitus position. Air-fluid levels can be key to diagnosing bowel obstruction.