新一代基于模型的迭代重建中肺特异性设置在亚mSv胸部CT检查中的应用

摘要

目的 比较自适应统计迭代重建(ASIR)、常规基于模型的迭代重建(MBIRc)、新一代基于模型的迭代重建(MBIRn)中肺特异性设置(MBIRRP20和MBIRNR40)重建算法对亚mSv胸部CT图像质量的影响.方法 收集接受两次胸部CT平扫的受检者30例.初检采用常规剂量(噪声指数=14)ASIR重建.复查采用低辐射剂量方案(噪声指数=28),分别采用标准算法和肺算法ASIR、MBIRc、MBIRRP20和MBIRNR40重建,重建层厚0.625 mm.在标准算法ASIR、MBIRc和MBIRNR40重建图像上测量胸廓入口层面、气管隆突下层面和肝门层面背部肌肉、皮下脂肪相同部位ROI的CT值与噪声(SD),并计算SNR,采用单因素方差分析比较各重建算法SD和SNR.于肺窗ASIR、MBIRc、MBIRRP20和纵隔窗标准算法ASIR、MBIRc、MBIRNR40进行噪声和细节结构清晰度5分法主观评分,并采用Wilcoxon符号等级检验进行统计学分析.结果 初检有效剂量为(3.01±1.89)mSv,复查有效剂量为(0.88±0.83) mSv,下降约70.76％.MBIRNR40图像噪声明显低于常规剂量ASIR、低剂量ASIR和MBIRc(P均＜0.05).MBIRNR40图像SNR绝对值明显大于常规剂量ASIR、低剂量ASIR和MBIRc(P均＜0.05).MBIRNR40的主观图像噪声评分低于常规剂量ASIR和MBIRc(P均＜0.05);MBIRn可更清晰地显示肺、纵隔及上腹部细节结构,评分高于MBIRc和ASIR(P＜0.05).结论 在胸部CT平扫时,与ASIR、MBIRc相比,MBIRn肺特异性设置中MBIRNR40可显著降低图像噪声并提高SNR,可减少辐射剂量约70％,在低剂量条件下,MBIRRP20可更好地显示肺内、MBIRNR40可更好地显示纵隔、上腹部细节结构.%Objective To assess image quality of adaptive statistical iterative reconstruction (ASIR),conventional modelbased iterative reconstruction (MBIRc) and a new lung-specific setting (MBIRRP20 and MBIRNR40) from the new version of model-based iterative reconstruction (MBIRn) in submillisievert chest CT comparing with ASIR in standard-dose.Methods Two chest CT examinations were performed with standard-dose and low-dose in 30 patients.Low-dose CT images were reconstructed with ASIR,MBIRc and MBIRn,while standard-dose CT images were reconstructed with ASIR only.Objective image noise and SNR were measured on the same part from the back muscle and subcutaneous fat which located at the level of thoracic entry,trachea carina and hepatic portal.Image quality of lung,mediastinum and upper abdomen structures were evaluated on a 5-point scale.The results were compared with one-way ANOVA and Wilcoxon signed-rank tests.Results The effective dose equivalent for standard-dose CT was (3.01 ± 1.89) mSv,compared with (0.88 ± 0.83) mSv for low dose CT,which decreased by 70.76％.The mean image noise for low-dose MBIRNR40 was significantly lower than that of conventional-dose ASIR,low-dose ASIR and MBIRc (P＜0.05).The mean SNR for low-dose MRIRNR40 was significant ly higher than that of conventional dose ASIR,low-dose ASIR and MBIRc (P＜0.05).The subjective image noise score was significantly lower than that of ASIR and MBIRc,and the score of sharpness of details of the structures score for low dose MBIRn was significantly better than that of the ASIR and MBIRc (P＜0.05).Conclusion MBIRNR40 can significantly reduce image noise and improve SNR compared to ASIR and MBIRc in low-dose,even better than ASIR in standard dose,which reduce radiation dose by about 70％.In low-dose,MBIRPP20 can well display lung structures,and MBIRNR40 can display mediastinal and the upper abdominal structures.