Enhanced CT Scan In Liver Using Different Noise Index And Iterative Reconstruction Algorithm With Different Body Mass Index: Imaging Quality And Radiation Dose

Objective : To investigate the differences in image quality and radiation dose in contrast-enhanced liver CT scans with different body mass index(BMI)by using different Noise Index(NI).Method:A total of 240 patients who would have contrast-enhanced liver CT scans were divided into two equal-sized groups: A(18kg/m2?BMI<24kg/m2)and group B(24 kg/m2 < BMI?31kg/m2)according to body mass index(BMI),each group had 120 patients.The two groups were randomly divided into four subgroups with an NI of 11,13,15 and 17,respectively.All patients underwent three phases hepatic contrast-enhanced liver CT scanning by tube voltage of 120 k Vp and automatic tube current modulation(ATCM)technology.All images were restructured with 50% adaptive statistical iterative reconstruction(ASIR).The signal-to-noise ratio(SNR)and contrast-to-noise ratio(CNR)were calculated after the late arterial,portal venous,and equilibrium phases were completed,Images were evaluated by two radiologists using a subjective 0–5 scale.Mean CT dose index of volume,dose-length product,and effective dose(ED)were calculated.SNR and CNR of images in different CT enhanced phase were compared with repeated measures ANOVA,CTDIvol,DLP and ED were compared with one-way ANOVA.Results:In group A,SNR,CNR and the subjective scores of later arterial phase images showed a statistical difference between NI=17 and the other subgroups(P<0.01),while portal venous phase and equilibrium phase showed no statistical differences between NI=17 and the other subgroups and no statistical differences among the other three subgroups with the three phases scans.The average ED were significantly lower in the NI=15 and N=17 subgroups than in NI=11 and N=13.Specifically,the ED of NI=15 and NI=17 was reduced by 57.56% and 61.54% compared to NI=11,respectively.In group B,SNR,CNR and the subjective image scores of the later arterial phase showed significant difference between NI=15 and NI=11,13(P<0.01),while portal venous phase and equilibrium phase showed no statistical differences between NI=15 and NI=11,13.The image quality of NI=17 was statistically significant with the other three subgroups in the later arterial phase,portal venous phase and equilibrium phase(P<0.01).The average ED of NI=13 and NI=15 was reduced by 26.41% and 45.31% compared to NI=11,respectively.Conclusion:A BMI—adjusted NI combined with the application of an iterative reconstruction algorithm—the ASIR—maintained image quality on liver CT,even at low radiation dose.