Patients with different body mass index underwent liver enhanced CT scan: the influence of different noise indexes combined with iterative recombination algorithm on image quality and radiation dose

Abstract

Objective To investigate the effect of different noise index (NI) combined with iterative recombination on the image quality and radiation dose of CT scan in patients with different body mass index (BMI). Method One hundred and sixty patients who had a liver CT enhanced scan were divided into group A (18 kg/m2 ≤ BMI< 24 kg/m2) and group B (24 kg/m2 ≤ BMI< 31 kg/m2) according to BMI, and each group had 80 patients. The two groups were randomly divided into 4 subgroups which NI value was 11, 13, 15 and 17 respectively. All images were restructured with 50% adaptive statistical iterative reconstruction. Subjective evaluation, objective evaluation [signal noise ratio (SNR) and contrast noise ratio (CNR)] and the effective dose of each group were recorded and calculated after the scan. ANOVA and Kruskal-Wallis test were used to evaluated the difference of imaging quality and radiation dose. Results In group A, the SNR, CNR and the subjective score of the later arterial phase images showed a statistical difference between NI= 17 group and other subgroups (P<0.05), while there was no statistical differences among the other three subgroups during three CT enhanced phase. The average ED of NI=15, 17 group were decreased by 57.56% (2.17/3.77) and 61.54% (2.32/3.77) compared with NI=11 group, respectively. In group B, the SNR, CNR and the subjective image scores of the later arterial phase showed a significant difference between NI=15 and NI=11, 13 group (P<0.05). There was a statistically difference of image quality in group NI=17 compared with the other three subgroups in the later arterial phase, portal venous phase and equilibrium phase (P<0.05). The average ED of NI= 13, 15 group was decreased by 26.41% (1.69/6.40) and 45.31% (2.90/6.40) compared with NI=11 group, respectively. Conclusion Upon maintaining diagnostic imaging quality, setting different NI according to BMI and applying the iterative reconstruction algorithm can effectively reduce the radiation dose of liver CT enhanced scanning. Key words: Tomography, X-ray computed; Radiation Dosage; Body weight; Noise index