肺动脉CT血管成像在双源CT大螺距模式下的低辐射剂量与低对比剂量研究

Study of Low Radiation Exposure Dose and Low Contrast Medium Dose in Pulmonary CT Angiography with High-Pitch Spiral Acquisition Mode of Dual Source CT

目的：研究肺动脉CT血管成像（CTPA）中，双源CT大螺距模式下低辐射剂量和低对比剂量的成像可行性。方法168例临床拟诊肺栓塞患者中，挑选BMI＜23 kg/m2的患者105例行CTPA。患者分为3组，每组35例，Ⅰ组：管电压80 kV，对比剂采用碘普罗胺（370 mgI/mL），图像重建算法为正弦确认迭代重建算法（SAFIRE）；Ⅱ组：管电压100 kV，对比剂采用碘克沙醇（320 mgI/mL），图像重建算法为滤过反投影重建法（FBP）；Ⅲ组：管电压80 kV，对比剂采用碘克沙醇（320 mgI/mL），图像重建算法为SAFIRE。105例患者中57例经CTPA诊断为肺栓塞，分别测量3组肺动脉1-3级分支、栓子及背部肌肉的CT值，并计算信噪比（SNR）及对比噪声比（CNR）。采用独立样本t检验来分别比较Ⅰ组和Ⅲ组、Ⅱ组和Ⅲ组的图像质量的SNR及CNR；同时比较Ⅰ组和Ⅲ组的碘摄入量、Ⅱ组和Ⅲ组的有效辐射剂量（ED）。利用Kappa检验分析2名医师分析各组CTPA图像质量的一致性。结果Ⅰ组肺动脉1-3级分支SNR及CNR值分别为8.4±2.7、7.2±2.5、6.8±3.3及7.1±1.2、6.4±1.4、5.8±4.5。Ⅱ组肺动脉1-3级分支SNR及CNR值分别为8.2±4.3、7.7±3.6、6.2±2.7及7.4±2.4、6.6±2.6、6.0±3.4。Ⅲ组肺动脉1-3级分支SNR及CNR值分别为8.7±1.8、7.5±3.4、6.6±2.3及7.7±3.8、6.7±1.1、5.6±3.9。Ⅰ组和Ⅲ组，Ⅱ组和Ⅲ组的SNR及CNR值差异无统计学意义（P＞0.05）。Ⅲ组较Ⅰ组碘摄入量下降14%，Ⅲ组较Ⅱ组辐射剂量减少45%，3组CTPA图像质量差异无统计学意义（P＞0.05）。57例CTPA诊断为肺栓塞患者定量分析显示，3组栓子SNR及CNR值分别为1.3±0.4、1.2±0.4、1.4±0.6及7.4±3.3、7.6±1.6、7.3±3.7，3组SNR及CNR值比较差异无统计学意义（P＞0.05）。2名医师的评价结果经Kappa检验，各组图像质量分析的一致性较好（P＜0.01）。结论在BMI＜23 kg/m2的患者中可以使用双源CT大螺距模式、80 kV、SAFIRE算法、碘克沙醇（320 mgI/mL）的低辐射剂量与低对比剂量扫描方式进行CTPA，在满足临床诊断的需要下最大程度地减少了辐射剂量及碘对比剂的用量，推荐作为常规扫描方式。

Objective To evaluate the feasibility of low radiation exposure and low contrast medium volume for pulmonary CT angiography with high-pitch spiral acquisition mode of dual source CT. Methods 105 patients whose BMI〈23 kg/m2 selected from 168 patients were randomly divided into 3 groups before they underwent CT pulmonary angiography （CTPA）, and there were 35 patients in each group. 57 patients were diagnosed with pulmonary embolism. 80 kV, Iopamidol （370 mgI/mL） and sinogram affirmed iterative reconstruction （SAFIRE）were used in groupⅠ. 100 kV, Iodixanol （320 mgI/mL） and filtered back projection （FBP） were used in groupⅡ. 80 kV, Iodixanol （320 mgI/mL） and SAFIRE were used in groupⅢ. CT value of pulmonary artery （grade 1-3） and muscles were measured. Corresponding signal to noise ratio （SNR） and contrast to noise ratio （CNR） were calculated. Independent-Sample Test was used to analyze statistical significance of image quality including SNR and CNR between the three groups. At the same time, mean effective radiation dose （ED） statistical significance between groupⅡand groupⅢand contrast dose between groupⅠand groupⅢwere analyzed by the same way. The inter-reader agreement of image quality was performed by Kappa test. Results SNR and CNR value was 8.4±2.7, 7.2±2.5, 6.8±3.3 and 7.1±1.2, 6.4±1.4, 5.8±4.5 in groupⅠ, 8.2±4.3, 7.7±3.6, 6.2±2.7 and 7.4±2.4, 6.6±2.6, 6.0±3.4 in groupⅡ, 8.7±1.8, 7.5±3.4, 6.6±2.3 and 7.7±3.8, 6.7±1.1, 5.6±3.9 in groupⅢ. There were no significant difference of image quality including SNR and CNR between groupⅠand groupⅢor between groupⅡand groupⅢ（P〉0.05）, whereas mean ED and contrast dose decreased 45%and 14%respectively in groupⅢ. There was no statistical difference for image quality of CTPA among the three groups （P〉0.05）. On quantitative analysis of 57 patients, SNR and CNR value of pulmonary clots was 1.3±0.4, 1.2±0.4, 1.4±0.6;7.4±3.3, 7.6±1.6, 7.3±3.7 in groupⅠ,Ⅱ, andⅢ, respectively. There was no statistical difference between three groups （P〉0.05）. Two physicians on CTPA images to assess the consistency of uniform height （P〈0.01）. Conclusion In the CTPA examination, the High-pitch spiral mode, 80 kV, SAFIRE, and Iodixanol （320 mgI/mL） can be used in those patients whose BMI〈23 kg/m2, it not only can reduce the overall radiation dose but also can minimize the amount of contrast agent but to meet the clinical requirement.