迭代重建技术在颅骨扫描中的应用及图像质量与辐射剂量的相关性研究

Application of Iterative Reconstruction in Skull Scanning and the Correlation Study of Image Quality and Radiation Dose

目的探讨迭代重建(IR)算法在颅骨扫描中对图像质量及辐射剂量的影响。方法选取2013年6月—2014年12月间潍坊市人民医院脑科医院因颅骨骨折或术后行颅骨修补的80例患者为研究对象,按照随机原则分为4组,每组20例。A组采用常规滤波反投影(FBP),B^D组为低剂量组,采用IR技术逐级降低管电流,使辐射剂量分别降低50%、60%、70%,并采用自适应性统计迭代重建技术(ASIR)重建;采用单因素方差分析比较各组客观评价指标[枕骨髁间隆起周围最厚骨皮质的平均值(CT值)、图像噪声值(SD)、信噪比(SNR)、对比噪声比(CNR)]及辐射剂量[CT剂量指数(CTDI)、CT剂量长度乘积(DLP)及有效辐射剂量(ED)]的差异;采用Kruskal-Wallis检验比较各组主观图像质量评分(对比度、边缘锐利度、主观噪声及图像总体质量,采用4分法)。结果4组的CT值、SD值、SNR、CNR比较,差异无统计学意义(P>0.05);2名放射科医师对4组图像的主观评分比较,对比度、锐利度、主观噪声及图像质量的Kappa值分别为0.73、0.74、0.76、0.80,显示一致性较好(Kappa>0.75);4组显示了良好的主观图像质量,各项评分≥3分,差异无统计学意义(P>0.05);4组CTDI、DLP、ED比较,差异有统计学意义(P>0.05)。结论 IR可以降低噪声,在扫描剂量降低70%的条件下仍可得到达到诊断要求的图像质量。

Objective To assess the impacts of Iterative Reconstruction（ IR） technique on the image quality and radiation dose for scull scanning reconstruction. Methods The research was conducted based on 80 patients who had suffered craniocerebral trauma or required skull repair. According to the principle of random distribution,the patients were divided into 4groups evenly,20 cases in each group. The control group（ Group A） was scanned by using the conventional tube current and reconstructed by using FBP. With step-by-step reduced tube current output,the Group B,C,and D were scanned with the same k Vp but the radiation doses were reduced by 50%,60% and 70% respectively, and were reconstructed by using ASIR. Quantitative measurements of image SNR and CNR were obtained in each group. The One-way Analysis of Variance（ ANOVA） was applied to the comparisons of objective evaluation indexes（ CT values,SD,SNR,CNR） and those of the differences of radiation dose（ CTDI, DLP, ED） between four groups. Moreover, the Kruskal-Wallis test was applied to comparisons of differences in subjective evaluations of Image Quality（ Contrast Ratio,Edge Sharpness,Subjective Noise,and Overall Image Quality） between four groups. Significance test of difference was also included（ a level of P 〈 0. 05 was considered to be statistically significant）. Results The differences in CT values, SD、 SNR, and CNR between four groups are insignificant（ P 〉 0. 05）. The kappa values of contrast,sharpness,noise,and image quality were found to be 0. 73,0. 74,0. 76,and 0. 80,respectively,which demonstrates favorable consistency（ Kappa 〉 0. 75）. Therefore,the four groups suggest good subjective IQ（ i≥3） and insignificant difference（ P 〉 0. 05）,and significant differences in CTDI、DLP、ED between the4 groups（ P 〈 0. 05）. Conclution The Iterative Reconstruction is instrumental for lowering the noise and is able to maintain the image quality satisfying the demands of diagnosing while the scanning dose is reduced by 70%.