Diagnostic accuracy of computed tomography using lower doses of radiation for patients with Crohn's disease.

Background & Aims: Magnetic resonance and ultrasonography have increasing roles in the initial diagnosis of Crohn's disease, but computed tomography (CT) with positive oral contrast agents is most frequently used to identify those with acute extramural complications. However, CT involves exposure of patients to radiation. We prospectively compared the diagnostic accuracy of low-dose CT (at a dose comparable to that used to obtain an abdominal radiograph) with conventional-dose CT in patients with active Crohn's disease.

Methods: Low and conventional dose CT of the abdomen and pelvis were acquired from 50 patients with Crohn's disease, referred from an inflammatory bowel disease service (20 male; median age, 34 years). Acute complications of Crohn's disease were suspected. Iterative reconstruction was performed on all CT datasets to facilitate dose reduction. Three radiologists reviewed the low-dose CT images before the conventional-dose CT images.

Results: The median effective dose (interquartile range) of radiation for the low-dose CT was reduced by 72% from that of conventional CT: from 3.5 mSv (3-5.08 mSv) to 0.98 mSv (0.77-1.42 mSv) (P < .001). As expected, the quality indexes of the low-dose images were inferior to those of the conventional-dose images, but no clinically significant diagnostic findings were missed with low-dose imaging. Follow-up CT examinations were recommended for 5 patients; 1 had a cervical tumor, 1 had a pancreatic lesion, and 3 had intra-abdominal abscess. In each case, the image obtained by low-dose CT was considered sufficient for diagnosis.

Conclusions: Although low-dose CT images are of lower quality than images obtained with conventional doses of radiation, no clinically significant diagnostic findings were missed from low-dose CT images of patients with Crohn's disease. The low-dose CT was obtained at a median effective dose equivalent to 1.4 abdominal radiographs.