多模型迭代重建算法对腹部体模CT扫描图像质量和辐射剂量的影响

Influence of adaptive statistical iterative reconstruction-V on image quality and radiation dose of abdominal CT in phantom

目的分析前置全模型迭代重建算法(ASIR-V)在腹部体模CT扫描中图像质量的变化规律及辐射剂量的降低程度,探讨优化图像质量和辐射剂量的最佳前置ASIR-V。方法采用腹部仿真体模和Revolution CT机。根据噪声指数(NI)设置(6、8、10、12、14)分为5组。每组设置0~100%(间隔10%)前置ASIR-V扫描和常规扫描(即不联合迭代),共获得55组图像。分析各NI组图像CT值、噪声、主观评分及辐射剂量随ASIR-V比例的变化规律。各NI组图像的主观评分比较采用秩和检验,CT值、噪声和辐射剂量比较采用单因素方差分析和配对t检验。结果在0~40%前置ASIR-V水平,NI为6、8、10组图像主观评分基本稳定,NI为12、14组图像主观评分呈略升高趋势;50%~100%前置ASIR-V,各组主观评分均呈逐渐降低趋势;NI为6、8、10组,超过70%前置ASIR-V图像主观评分降至3分以下,NI为12、14组,超过60%前置ASIR-V主观评分降至3分以下;NI为6、8、10组,常规扫描图像主观评分与40%前置ASIR-V图像差异无统计学意义(P=0.626、0.915、0.514),NI为12、14组,常规扫描图像主观评分略低于40%前置ASIR-V图像(P=0.041、0.036);各NI组常规扫描图像主观评分均优于60%前置ASIR-V图像((P=0.021、0.012、0.015、0.014、0.007))。各NI组中不同部位CT值、噪声随前置ASIR-V比例的增高呈基本稳定状态(P均>0.05)。各NI组CTDIvol随前置ASIR-V比例的增高,呈逐渐下降趋势。40%、50%和60%前置ASIR-V比例条件下,CTDIvol较常规扫描组下降比率分别为49.82%、62.51%、71.63%。结论前置ASIR-V可在保证图像质量的条件下明显降低辐射剂量;腹部前置ASIR-V比例推荐40%~60%。

Objective To evaluate the influence of preset adaptive statistical iterative reconstruction V （ASIR-V） tech- niques on image quality and radiation dose reduction of abdominal CT in phantom, and to investigate the optimal ASIR-V level. Methods Abdominal anthropomorphic phantom was scanned using Revolution CT, when noise index （NI） were set as 6, 8, 10, 12 and 14, respectively. Then 0-100% ASIR-V and conventional scan was performed and 55 sets of images were obtained. CT value, noise, subjective score and radiation dose were recorded, and the optimal ASIR V was obtained. Subjective scores of images in each group were compared using rank sum test, and CT value, noise and radiation dose were compared with one way ANOVA and paired t test. Results The image subjective score unchanged when NI was 6, 8 or 10, slightly increased when NI was 12 and 14 with 0 40% ASIR-V, and decreased above 50% ASIR-V at all NI. When NI was 6, 8 or 10, more than 70% ASIR-V image subjective score fell below 3 points. When NI was 12 or 14 group, more than 60% ASIR V subjective score fell below 3 points. The image quality score of conventional scan had no difference with 40% ASIR-VwhenNIwas 6, 8 or 10, respectively （P=0.626, 0.915, 0.514）, and inferior to 40% ASIR V when NI was 12 or 14 （P=0. 041, 0. 036）, while in all NI group, image quality score of conventional scan was superior to 60% ASIR-V （P=0. 021, 0. 012, 0. 015, 0. 014, 0. 007）. CT values and image noises had no significant differences in different parts in all NI groups （all P〉0.05）. CT dose index volume （CTDIvol） continuing decreased with ASIR-V. Compared with that of conventional scan, at 40%, 50% and 60% ASIR-V, CTDIvol reduced by 49.82%, 62.51% and 71.63%, respectively. Conclusion Preset ASIR V can reduce radiation dose obviously while maintaining the overall image quality, and 40%-60 % ASIRV can be recommended for abdominal CT in clinical application.