In the case of bowel perforation with peritonitis, which imaging study is most effective?

A CT scan of the abdomen is the most effective imaging study for evaluating bowel perforation with peritonitis. This method provides high-resolution images that can clearly illustrate the presence of air or fluid in the abdominal cavity, as well as any associated complications such as abscesses. The sensitivity and specificity of CT scans make them superior for identifying perforations in the gastrointestinal tract and understanding the overall extent of peritonitis.

In contrast, an abdominal ultrasound can be useful, especially in specific clinical settings or for patients who are unable to undergo CT scanning due to contraindications. However, ultrasound is generally less reliable in detecting subtle perforations or intra-abdominal free air. X-ray imaging can indicate free air under certain conditions but lacks the detailed visualization provided by a CT scan. MRI is not typically used as a first-line imaging study for this type of acute condition due to its higher cost and limited use in emergent scenarios related to bowel perforation, making it less practical in this context.