Radiation dose reduction and image quality in pediatric abdominal CT with kVp and mAs modulation and an iterative reconstruction technique

Abstract

OBJECTIVE: The objective of this study was to compare the radiation dose and image quality of pediatric abdominal computed tomography (CT) using a protocol reconstructed with filtered back projection (FBP) and a protocol with both kVp and mAs modulation and sinogram-affirmed iterative reconstruction (SAFIRE). MATERIALS AND METHODS: We retrospectively reviewed pediatric abdominal CT examinations performed with both kVp and mAs modulation. These raw data were reconstructed with SAFIRE at different strengths from 2 to 4 (SAFIRE groups 2-4). Another set of age/sex-matched pediatric abdominal CT examinations were also reviewed, which were performed during the same period with only mAs modulation and FBP (control group). The radiation dose and image quality were compared between groups. The image quality was objectively evaluated as the noise measured in the liver, aorta, and spleen at the level of the main portal vein and the image quality was subjectively reviewed by two radiologists for diagnostic acceptability using a four-point scale (0: unacceptable; 1: worse than the control group, but acceptable; 2: comparable with the control group; and 3: better than the control group). An independent t test was used in order to compare the radiation dose. An independent t test with Bonferroni correction and generalized estimating equations were used for the comparison of the objective and subjective image quality, respectively. RESULTS: Twenty-nine patients (M:F=19:10; mean age, 10.0 years) were enrolled in each group. The SAFIRE group, using the size-specific dose estimates calculation method showed a 64.2% radiation dose reduction (from 8.1 to 2.9 mGy, P<.05), compared with the results of the control group. The objective image noise of the SAFIRE groups 2 and 3 was comparable to that of the control group. The subjective image quality was the best in SAFIRE group 3 [odds ratio (OR) 3.015, P<.001 when comparing to SAFIRE group 0; OR 1.513, P<.001 when comparing to SAFIRE group 2]. CONCLUSIONS: Image acquisition with both kVp and mAs modulation and iterative reconstruction using SAFIRE with strength 3 can preserve the objective and subjective image quality of pediatric abdominal CT scans with less than half the radiation dose.