低剂量CT胸部扫描最佳噪声指数及适应迭代重建权重的选择分析

The best noise index combined with ASIR weighting selection in low-dose chest scanning

目的 探讨基于体质指数（BMI）低剂量CT胸部扫描最佳噪声指数（NI）与自适应迭代重建（ASIR）权重组合的选择.方法 收集自2014年5至12月郑州大学第一附属医院体检科行胸部CT平扫的健康体检者200名,随机分为常规剂量组（A组NI15结合30％ ASIR）和三个低剂量组（B组NI25结合40％ ASIR、C组NI30结合50％ ASIR、D组NI35结合60％ ASIR）,每组50名;BMI（kg/m2）分为三组：BMI＜ 18.5组、18.5≤BMI≤25组和BMI＞ 25组.基于BMI比较低剂量组与常规剂量组信噪比（SNR）、对比信噪比（CNR）、剂量容积指数（CTDIvol）、剂量长度乘积（DLP）、有效剂量（ED）及各组主观评分.SNR、CNR、CTDIvol、DLP及ED各组间比较用方差分析,医师对图像一致性检验用Kappa分析.结果 SNR、CTDIvol、DLP及ED随着噪声指数的升高逐渐减小,差异均有统计学意义（均P＜0.05）;两名医师主观评分的一致性检验Kappa值为0.888.BMI＜ 18.5 kg/m2时四组主观评分均在3分以上;18.5 kg/m2≤BMI≤25 kg/m2组在ABC组中主观评分均在3分以上.BMI＞ 25 kg/m2组在AB组中主观评分均在3分以上.结论 当BMI＜ 18.5 kg/m2时,选择NI35结合60％ ASIR;18.5 kg/m2≤BMI≤25 kg/m2时,选择NI30结合50％ ASIR;BMI＞ 25 kg/m2时,选择NI25结合40％ASIR为最佳参数组合既可以明显降低辐射剂量又可保证图像质量.

Objective To discuss the best noise index combined with ASIR weighting selection in low-dose chest scanning based on BMI.Methods 200 patients collected from May to December 2014 underwent non-contrast chest CT examinations,they were randomly assigned into standard dose group （Group A,NIl5 combined with 30% ASIR） and low-dose groups （Group B,NI25 combined with 40% ASIR,Group C,NI30 combined with 50% ASIR,Group D,NI35 combined with 60% ASIR）,50 cases in each group;the patients were assigned into three groups based on BMI （kg/m2）：BMI 〈 18.5;18.5 ≤ BMI ≤ 25;BMI 〉25.Signal-to-nosie ratio （SNR）,contrast-to noise ratio （CNR）,CT dose index volume （CTDIvol）,dose-length product（DLP）,effective dose（ED） and subjective scoring between the standard and low-dose groups were compared and analyzed statistically.Differences of SNR,CNR,CTDIvol,DLP and ED among groups were determined with ANOVA analysis and the consistency of diagnosis with Kappa test.Results SNR,CTDIvol,DLP and ED reduced with the increase of nosie index,the differences among the groups were statistically significant （P 〈 0.05）.Kappa value of the two reviewers were 0.888.Subjective scoring of four groups were all above 3 points in BMI 〈 18.5 kg/m2 group;subjective scoring of ABC groups were all above 3 points in 18.5 kg/m2 ≤BMI≤25 kg/m2 group and subjective scoring of AB groups were all above 3 points in BMI 〉25 kg/m2 group.Conclusions NI35 combined with 60%ASIR in BMI 〈 18.5 kg/m2 group;NI30 combined with 50% ASIR in 18.5 kg/m2 ≤BMI≤25 kg/m2 group;NI25 combined with 40%ASIR in 18.5 kg/m2 ≤BMI ≤25 kg/m2 group were the best parameters combination which both can significantly reduce the radiation dose and ensure the image quality.