低浓度对比剂能谱CT单能量成像对提高门静脉图像质量的研究

Study on the effect of monochromatic images with best contrast-to-noise ratio using spectral CT for improving the imaging quality of portography using low-concentration contrast medium

目的:探讨宝石CT能谱成像最佳对比噪声比(CNR)单能量图像对提高低浓度对比剂门静脉成像质量的应用价值。方法:将符合纳入标准的136例患者随机分为2组,A组采用高浓度对比剂(350mg I/100mL)和常规CT扫描(1.25mm层厚)、B组采用低浓度对比剂(270mg I/100mL)和宝石CT能谱成像(GSI)。由两位放射科医师采用双盲法分别测量两组图像上门静脉左支、右支和肝实质的CT值及图像噪声,对两位观察者的测量结果采用组内一致性系数(ICC)进行分析;采用较高年资观察者的测量结果,计算门静脉的对比噪声比(CNR),并对两组的测量结果及CNR值分别行t检验;经图像后处理,分别获得两组图像的VR和MIP重组图像并进行图像质量的主观评分,对2位医师的图像质量评分采用Kappa检验,并采用较高年资观察者的评分结果和秩和检验法对2组间的图像质量进行比较。结果:B组中门静脉最佳CNR单能量图像的能量水平集中在50KeV左右。两位观察者测量数据的一致性较好(ICC>0.75)。A组中门静脉左支、门静脉右支和肝实质的CT值及背景噪声(SD值)分别为(178.38±27.25)、(174.78±24.66)、(116.13±17.01)和(32.78±4.72)HU,B组分别为(334.01±58.74)、(328.51±55.78)、(187.89±32.23)和(39.12±10.05)HU,这4个测量指标在两组间的差异均有统计学意义(P<0.05)。B组中门静脉左、右支与肝实质的CNR(分别为4.08±1.90和3.93±1.80)均高于A组(分别为1.92±0.68和1.80±0.59),两组间差异有统计学意义(P均<0.01)。两位医师对重组图像的主观评价结果一致性较好(A组Kappa值为0.900,B组Kappa值为0.902);两组的图像质量评分分别为3.26±0.50和3.23±0.43,差异无统计学意义(P=0.896)。结论:能谱CT能提供多组单能量图像,且在降低对比剂浓度的前提下,GSI最佳CNR单能量图像能显著提高门静脉与肝实质的对比噪声比,很好地显示门静脉及其分支。

Objective：To investigate the effect of spectral CT monochromatic images with the best contrast-to-noise ratio（CNR）for improving the imaging quality of portography using low-concentration contrast medium.Methods：According to the inclusion criteria,136 patients were selected and randomly divided into two groups for portography：in group A,contrast medium with high concentration（350mg I/100mL）and conventional CT were used;and in group B,low-concentration contrast medium（270mg I/100mL）and gemstone spectral imaging（GSI）were used.CT value of liver parenchyma,left-and right-portal vein,and image noise on portography images were measured independently and blinded by two radiologists,and the results of two observers were analyzed with intra-class correlation coefficient（ICC）.The CNR of the left-and right-portal vein was calculated using the data from the senior doctor,and independent t-test were used to compare the differences of the indexes mentioned above between the two groups.Then the data were post-processed using volume rendering（VR）and maximum intensity projection（MIP）methods.Image quality of portography in two groups was evaluated on a five-point scale by two radiologists.The inter-observer agreement of image quality grade was analyzed by Kapppa test.Then image quality of the two groups was compared by the Wilcoxon test using the data from the senior doctor.Results：In group B,the monochromatic images at 50 KeV were found to have the best CNR.The agreements of the value of the three indexes measured by the two observers were good all（ICC0.75）.The CT value of left portal vein、right portal vein and liver parenchyma,and image noise of group A were（178.38±27.25）,（174.78±24.66）,（116.13±17.01）and（32.78±4.72）HU,and those of group B were（334.01±58.74）,（328.51±55.78）,（187.89±32.23）and（39.12±10.05）HU,there were significant differences between the two groups（P〈0.05）.The CNRs of left-and right portal vein to liver parenchyma of group A（1.92±0.68 and 1.80±0.59,respectively）were lower than those of group B（4.08±1.90and3.93±1.80）with statistic difference between the two groups（P〈0.01）.The agreement of the image quality grading between the two observers was good（In group A,Kappa value=0.900;in group B,Kappa value=0.902）.The image quality scores of group A and B were 3.26±0.50 and 3.23±0.43 respectively,there was no significant difference between the two groups（P=0.896）.Conclusion：Compared with conventional MSCT,spectral CT imaging can provide multiple sets of single-energy images and improve CNR and image quality of portography using low concentration of contrast medium.