The news was mixed for CT in the emergency department in research presented Wednesday at the RSNA meeting. CT was found to be better than ultrasound for diagnosing ER patients with abdominal pain, but radiation dose can be drastically reduced for patients suspected of appendicitis, according to authors of several studies.

In a study comparing CT and ultrasound for diagnosing acute abdominal pain, CT scans provided greater sensitivity but more false-positive urgent diagnoses while ultrasound had more false negatives in 1021 patients who presented in the ER with acute abdominal pain and suspected appendicitis. Based on the findings, the investigators consider CT the modality of choice for detecting urgent disease, although the urgency may be overestimated.

In a related study, researchers used the same patient base to develop a decision model for use of CT. They analyzed three scenarios for use of CT, based on clinical predictors, and found that selective CT use could lower the negative appendectomy rate and improve its efficiency.

CT is not used for all patients with suspected appendicitis and a negative appendectomy rate ranging from 12% to 16% is reported.

In another study of 131 patients with suspected appendicitis, researchers compared standard and (simulated) low dose, with and without oral /and or intravenous contrast.

Results showed that the protocol had little effect on diagnosis, leading to the conclusion that radiation dose should be reduced to 30 mAs from 100 mAs in this situation. Results also showed that when contrast material was used, fewer signs were misclassified, and appendix visualization and the readers' confidence in their diagnosis were higher.