能谱CT最佳单能量成像技术降低下肢动脉成像对比剂用量的可行性

Application of gemstone optimal monochromatic imaging technique in reducing the amount of contrast agent for lower extremity angiography: a clinical feasibility study

目的探讨能谱CT最佳单能量成像技术在下肢动脉成像中个体化降低对比剂用量的可行性。方法前瞻性连续收集下肢CTA检查患者75例,按扫描方式及对比剂用量随机分为传统CT常规剂量组、能谱CT常规剂量组及能谱CT低剂量组。传统CT组、能谱常规剂量组对比剂用量为2 ml/kg,注射速率为3.5 ml/s,扫描方式、重建方法前者采用120 k Vp、滤波反投影(FBP)技术,后者采用能谱模式、50%自适应统计迭代重建(ASi R)技术;能谱低剂量组对比剂用量、注射速率均降低20%,采用能谱模式、50%ASi R技术。检测3组图像靶血管CT值,并记录对比噪声比(CNR)、背景噪声(BN)、剂量长度乘积(DLP)、有效辐射剂量(ED)、摄碘量及注射速率,采用单因素方差分析结合Bonferroni法进行差异性检验。采用Kruskal-Wallis检验对3组图像质量主观评分进行对比分析。结果本研究纳入60例患者,每组20例。能谱常规剂量组图像有着最佳CT值、CNR、BN(P<0.01),但BN与能谱低剂量组间差异无统计学意义(P>0.05);能谱低剂量组CT值、CNR除胫前动脉(P=0.162,P=0.376)外,均高于传统CT组(P<0.05)。两能谱组ED均显著低于传统CT组(P<0.01),但两能谱组间差异无统计学意义(P>0.05)。能谱低剂量组摄碘量、注射速率均显著低于能谱常规剂量组、传统CT组(P<0.01)。医师1、2对3组图像主观评分分别为82分、95分、90分和80分、96分、89分,差异有统计学意义(H=14.954,P<0.01;H=17.726,P<0.01),能谱常规剂量组有最佳图像质量,能谱低剂量组图像质量优于传统CT组(P<0.05)。结论能谱CT最佳单能量成像与传统螺旋CT相比,可提供更好的CNR及图像质量,在保证下肢动脉成像临床诊断的基础上明显降低辐射剂量,同时个性化减少对比剂摄入量。

Objective To investigate the clinical feasibility of using gemstone spectral image （GSI） technique to reduce the individual dose of contrast agent in performing lower extremity angiography. Methods Among the consecutive 75 patients receiving lower extremity CTA examination, 60 patients were enrolled in this study. According to the scanning method and contrast dosage, the 60 patients were prospectively and randomly divided into the conventional CT routine-dose group （n=20）, GSI routine-dose group （n=20） and GSI low-dose group （n=20）. In the conventional CT routine-dose group and GSI routine-dose group, the dosage of contrast medium was 2 ml/kg and the injection rate was 3.5 ml/s. Scanning with 120 kVp and reconstruction with filter back projection （FBP） technology were used in the conventional CT routine-dose group, while scanning with spectrum mode and reconstruction with 50% adaptive statistical iterative reconstruction （ASiR） technology were used in the GSI routine-dose group. In the GSI low-dose group, the dosage of contrast medium and the injection rate were 1.6 ml/kg and 2.8 ml/s respectively, and scanning with spectrum mode and reconstruction with 50% ASiR technology were adopted. The target vessel CT values of three sets of images were determined, the contrast-to-noise ratio （CNR）, the background noise （BN）, the dose length product （DLP）, the effective dose （ED）, the iodine intake dose and the injection rate were calculated and compared between each other among the three groups. Single factor variance analysis and Bonferroni correction method were used to statistically analyze the resuhs. By using Kruskal-Wallis test, the subjective scores of three sets of images were compared between each other among the three groups. Results According to exclusion criteria, 60 patients were finally enrolled in this study. The images of GSI routine-dose group had the best CT value, CNR and BN （P〈0.01）, but there was no statistically significant difference in BN between GSI routine-dose group and GSI low-dose group （P〉0.05）. Both the CT value and CNR, except anterior tibial artery （P=0.162 and P=0.376 respectively）, in the GSI low-dose group were higher than those in the conventional CT routine-dose group （P〈0.05）. The ED values of both GSI groups were lower than that of the conventional CT routine-dose group （P〈0.01）, although no statistically significant difference in ED value existed between the two GSI groups （P〉0.05）. The iodine intake dose and injection rate of the GSI low- （lose group were strikingly lower than those of the conventional CT routine-dose group and the GSI low-dose group （both P〈0.01 ）. The subjective scores of three sets of images evaluated by two physicians were 82, 95, 90 points and 80, 96, 89 points respectively, the differences were statistically significant （H=14.954, P〈 0.01 ; H=17.726, P〈0.O1）. GSI routine-dose group had the best image quality, and the image quality of GSI low-dose group was superior to that of conventional CT routine-dose group （P〈0.05）. Conclusion Compared with conventional spiral CT scanning, gemstone optimal monochromatic imaging technique can obtain more optimal CNR and image quality, meanwhile, the radiation dose can be remarkably reduced while the imaging quality of lower extremity angiography can meet the requirements of making clinical diagnosis, moreover, individual intake of iodine can be reduced.