The first test should be plain films (3 views) of the abdomen to include an upright chest for the detection of free air. A lateral decubitus view of the abdomen is an alternative to the chest x-ray if necessary. Frequently bowel obstruction will improve or resolve with NG suction, and only serial plain films are required to assess progress. If obstruction worsens or fails to resolve, an urgent small bowel series may be useful to evaluate the jejunum and ileum. A single contrast barium enema is the alternative examination if the site of obstruction is felt to be in the colon. The plain films will frequently determine upper vs. lower obstruction and guide these imaging decisions. Other modalities such as CT may be useful as second line or follow-up examinations.