CT低剂量迭代算法对泌尿系结石CT值影响的实验研究

Study on impacts of low-dose CT iterative algorithm on urinary calculi CT value

目的探讨CT低剂量联合迭代算法对泌尿系结石CT值的影响。方法搜集泌尿外科手术后结石60枚,将其用蒸馏水清洗干净,自然晾干、编号,放于猪肾内并记录位置,将埋有结石的猪肾标本放于组织模型中行CT扫描。常规剂量组:120k V,400m As,采用滤波反投影算法(filtered back projection,FBP)薄层重建;低剂量组:(A组:120k V,200m As;B组:120k V,150m As;C组:120k V,100m As)分别行FBP及迭代算法i Dose(2、4、6级)薄层重建。记录CT容积剂量指数(CTDIvol)、剂量长度乘积(DLP)、计算有效剂量(ED);测量图像的客观噪声值及结石CT值并进行统计学分析。结果低剂量各组的CTDIvol、DLP、ED与常规组比较差异有统计学意义(P<0.05);不同管电流、不同重建算法下测得的结石CT值之间比较差异无统计学意义(P>0.05);随着管电流的降低,图像噪声增大,在同一管电流下,i Dose重建的图像噪声与FBP图像噪声比较差异有统计学意义(P<0.05),且i Dose等级越高,图像噪声越低。结论应用迭代重建算法i Dose可以明显改善低剂量图像噪声,且不影响泌尿系结石CT值测量的准确性。

Objective To study the impacts of low-dose CT joint iterative algorithm on urinary calculi CT values. Methods A total of 60 stones were collected after urologic surgical procedures. They were cleaned up by distilled water,dried in the air,numbered and put into the pig kidneys,as well as recording the positions. Those pig kidney samples with stones were placed in a tissue model and performed the CT scan. Filtered back projection（ FBP） thin-slice reconstruction was carried out in the conventional dose group with 120 k V and 400 m As while FBP and i Dose（ grade 2,4 and 6） iterative algorithm thin-slice reconstruction were carried out respectively in the low-dose group（ group A： 120 k V and 200 m As; group B： 120 k V and 150 m As; group C：120 k V and 100 m As）. CTDIvol and DLP were recorded and ED was calculated. Objective noise level of images and the CT values of calculi were measured for statistical analysis. Results Compared the CTDIvol,DLP and ED in each low-dose group with the conventional group,the difference had statistical significance（ P〈0. 05）. The difference between calculus CT values were measured under different tube current and different reconstruction algorithms had no statistical significance（ P〈0. 05）. Along with decreases of tube current,the image noise increased. Under a same tube current,the difference of i Dose reconstructive image noise and FBP image noise had statistical significance（ P〈0. 05）. Moreover,the higher the level of i Dose,the lower the image noise will be. Conclusion i Dose can significantly improve the low-dose image noise and accurately measure the CT values of urinary calculi by using the iterative algorithm.