Dose-modified 256-MDCT of the abdomen using low tube current and hybrid iterative reconstruction

Abstract

Rationale and objectives: To evaluate the performance of hybrid iterative reconstruction technique (h-IRT) on image quality (IQ) in abdominal dose-modified (DM) scans in phantom and in patients in comparison to filtered back projection (FBP).

Materials and methods: An anthropomorphic phantom was scanned using various kVp (80-140) and mAs (25-100) settings. Images were reconstructed with FBP and h-IRT levels (1-6). In 69 adults (59.6 ± 13.54 years; 20 male, 49 female), DM computed tomography (CT) scans were performed using 120 kVp and 100-120 mAs. In 25/69, 5-mm FBP and h-IRT (levels 1-4 and 5) images were analyzed to validate IQ. The subsequent 44/69 had FBP and h-IRT (level 4) images reconstructed. Two readers evaluated 188 image series for IQ, noise, and artifacts. Objective and subjective data were analyzed using t-test and Wilcoxon signed-rank test, respectively. In 46/69 patients, prior dose CT was available for dose comparison.

Results: In the phantom, noise reduction ranged from 12% (h-IRT level 1) to 50% (level 6). In patients, h-IRT level 4 images were rated diagnostic in 69/69 exams but DM-FBP images were found nondiagnostic in 20/69 patients. The size-specific dose estimate (SSDE) was reduced by 55% in the dose-modified CT group, (SSDE:4.55 ± 1.15 mGy) over the prior dose protocol (SSDE:10.21 ± 3.5 mGy, P < .0001).

Conclusion: h-IRT improved IQ in abdominal DM-CT scans in phantom and in patients. Dose improvements were greater in smaller patients than larger ones.

Keywords: Radiation dose; abdomen; computed tomography; image quality; iterative reconstruction.