Reducing abdominal CT radiation dose with adaptive statistical iterative reconstruction technique

Abstract

Purpose: To assess radiation dose reduction for abdominal computed tomography (CT) examinations with adaptive statistical iterative reconstruction (ASIR) technique.

Materials and methods: With institutional review board approval, retrospective review of weight adapted abdominal CT exams were performed in 156 consecutive patients with ASIR and in 66 patients with filtered back projection (FBP) on a 64-slice MDCT. Patients were categorized into 3 groups of <60 kg (n = 42), 61 to 90 kg (n = 100), and >or=91 kg (n = 80) for weight-based adjustment of automatic exposure control technique. Remaining scan parameters were held constant at 1.375:1 pitch, 120 kVp, 55 mm table feed per rotation, 5 mm section thickness. Two radiologists reviewed all CT examinations for image noise and diagnostic acceptability. CT dose index volume, and dose length product were recorded. Image noise and transverse abdominal diameter were measured in all patients. Data were analyzed using analysis of variance.

Results: ASIR allowed for an overall average decrease of 25.1% in CT dose index volume compared with the FBP technique (ASIR, 11.9 +/- 3.6 mGy; FBP, 15.9 +/- 4.3 mGy) (P < 0.0001). In each of the 3 weight categories, CT examinations reconstructed with ASIR technique were associated with significantly lower radiation dose compared with FBP technique (P < 0.0001). There was also significantly less objective image noise with ASIR (6.9 +/- 2.2) than with FBP (9.5 +/- 2.0) (P < 0.0001). For the subjective analysis, all ASIR and FBP reconstructed abdominal CTs had optimal or less noise. However, 9% of FBP and 3.8% of ASIR reconstructed CT examinations were diagnostically unacceptable because of the presence of artifacts. Use of ASIR reconstruction kernel results in a blotchy pixilated appearance in 39% of CT sans which however, was mild and did not affect the diagnostic acceptability of images. The critical reproduction of visually sharp anatomic structures was preserved in all but one ASIR 40% reconstructed CT examination.

Conclusion: ASIR technique allows radiation dose reduction for abdominal CT examinations whereas improving image noise compared with the FBP technique.