儿童低剂量胸部CT中自适应迭代重建权重最佳阈值的初步研究

Preliminary Study on the Optimization of Image Quality of Low Dose Chest CT Scanning Using Different Weighted ASIR

目的比较自适应迭代重建技术（ASIR）不同权重重建图像对儿童低剂量胸部CT的图像质量和噪声的影响。方法回顾性分析80例应用低剂量扫描的儿童胸部CT影像，根据年龄分为4组，0—12个月预设噪声指数12，〉1—2岁预设噪声指数15，3～6岁预设噪声指数17，7—17岁预设噪声指数20。将所有图像经ASIR重建，以10％为步涨值，重建为0％～100％的11组图像，0％即传统的滤过反向投影重建方法，测量同一图像层面的左心室及背部肌肉客观噪声值，同时由两位医师分别用5分制主观评价纵隔窗及肺窗图像主观质量和主观噪声程度，3分及以上为可接受的图像。通过统计学分析不同ASIR权重与客观噪声值及图像主观质量之间的关系、不同年龄组间的客观噪声的差异。结果图像客观噪声值及图像主观噪声评分随着ASIR权重的提升而降低，同时图像主观质量也有改善，图像主观质量最佳权重为纵隔窗60％，肺窗70％。结论应用ASIR可以在儿童低剂量胸部CT扫描时明显降低图像噪声，提高图像质量，60％-70％权重的重建图像可以达到剂量与图像质量较好的平衡。

Objective To evaluate the influence of image reconstruction using different weighted adaptive statistical it- erative reconstruction （ASIR） technique on the image quality and noise in low dose chest CT scanning in children. Meth- ods The imaging materials of low dose chest CT scanning in 80 children were reviewed. According to the age, the patients were divided into 4 groups. Group 0 - 12 months, default noise index （NI） of 12 was used; group 1 -2 years, default NI of 15 was used; group 3 -6 years, default NI of 17 was employed; and group 7 - 17 years, default NI of 20 was adopted. All images were reconstructed with ASIR. As capable of generating images with a mix of ASIR and FBP reconstruction algo- rithms, the mix varied from 0% to 100% ASIR in 10% increments. Quantitative noise was calculated by measuring the standard deviation in a circular region of left ventricle and muscle in the same slice. The subjective image quality and image noise at mediastinal window and lung window were assessed on a 5 point scale by two observers, and a score greater than or equal to 3 was considered to be clinically acceptable. The relationships between the different ASIR weights and the objec- tive noise value as well as with the subjective image quality were statistically analyzed. The differences in objective noise value between different age groups were also evaluated. Results The image objective noise value and the image subjective noise ratings decreased with the increasing of ASIR weight, while the subjective image quality became improved. The opti- mal weight for getting the best subjective image quality was 60% for mediastinal window and 70% for lung window. Con- clusion Use of ASIR for children chest low dose CT scanning, the image noise can be significantly reduced and the image quality can be well improved. The reconstructed images using ASIR of 60% -70% weight have better image quality.