双层探测器光谱CT冠状动脉支架成像的最适虚拟单能量及对比剂浓度的模体研究

Study on the optimal keV and contrast agent concentration in coronary stents with a dual-layer spectral detector CT in vitro

目的探讨双层探测器光谱CT虚拟单能量成像对离体冠状动脉支架显示的最适能级及对比剂浓度。方法选取不同材质18枚支架,植入人造模拟冠状动脉血管内,配置常规浓度、低浓度(常规剂量的1/2)对比剂分别填充。行光谱CT扫描,常规浓度及低浓度进行50~100 keV(间隔10 keV)、120 keV单能级重建,分别记为A50~100、120 keV组和B50~100、120 keV组;另一组常规浓度数据进行常规iDose4重建,记为conv组。对图像进行主观评价,包括支架结构评分(Likert 5分法)及支架内管腔评分(Likert 4分法);客观评价包括背景噪声、对比噪声比(CNR)及支架内径差(ALN)。采用Kruskal-Wallis H检验和析因设计方差分析统计分析各组之间主观和客观评价指标差异。结果A80、90 keV组[(3.56±0.64)、(4.11±0.58)分]和B90 keV组[(3.61±0.50)分]支架结构评分显著优于其他组(P均<0.01),其中A90 keV组评分最高。支架内腔评分显示A70 keV组[(3.61±0.50)分]与B70 keV组[(3.47±0.63)分]均显著优于其他组(P均<0.01),A70 keV组评分最高。以能级为主效应分析,A组、B组及conv组间噪声、CNR及ALN相比,差异均有统计学意义(F=83.74、23.95、24.63,P均<0.01)。A70、80、90 keV组[(11.43±0.48)、(11.81±0.34)、(12.01±0.33)HU]和B70、80、90 keV组[(11.50±0.31)、(11.58±0.18)、(12.13±0.30)HU]图像背景噪声显著低于其他各组(P均<0.01),6组组间比较差异无统计学意义(P均>0.05),且A70 keV组的噪声最小。A50、60、70 keV组(26.85±5.19、26.03±4.29、24.46±5.40)及B50、60、70 keV组(25.88±5.67、24.18±5.46、24.91±7.67)支架管腔内CNR值显著高于其他组,差异均有统计学意义(P均<0.01),6组组间比较差异无统计学意义(P均>0.05)。且A50 keV组支架管腔内CNR值最高。A90、100、120 keV组[(32.22±6.16)%、(30.79±5.55)%、(27.05±4.47)%]ALN值高于conv组[(41.76±6.00)%],差异均具有统计学意义(P均<0.01)。A90、100、120 keV组与B90、100、120 keV组[(34.34±5.73)%、(33.95±5.46)%、(33.92±5.45)%]ALN值均较其他亚组低,差异均有统计学意义(P均<0.01),6组组间比较差异无统计学意义(P均>0.05),且A120 keV组ALN值最低。结论关于支架模体成像,DLCT单能量较混合能量成像质量更佳。行DLCT扫描时,90 keV(支架结构显示)与70 keV(支架管腔显示)结合重建可在浓度减半时不降低成像质量。

Objective To investigate the optimal monoenergetic level of spectral reconstructions and contrast agent concentration for the structure and lumen of isolated coronary stents on a dual-layer spectral detector CT(DLCT).Methods Eighteen scaffolds of different materials were implanted into the artificial simulated coronary artery,and were filled with conventional and low concentration contrast agents(1/2 of the conventional dose).Spectral CT scan was performed,and 50-100 keV(interval 10 keV)and 120 keV single-level reconstruction were performed at the conventional concentration and low concentration,which were recorded as A50-100,120 keV group and B50-100,120 keV group respectively;Another group of conventional concentration data was reconstructed with conventional iDose4,which was recorded as conv group.The image was evaluated subjectively,including stent structure score(Likert 5-score)and stent lumen score(Likert 4-score);objective evaluation,including background noise,contrast noise ratio(CNR)and stent inner diameter difference(AlN).The differences of subjective and objective evaluation indexes were analyzed.Results The stent structure scores of A80,90 keV group[(3.56±0.64),(4.11±0.58)points]and B90 keV group[(3.61±0.50)points]were significantly better than those of other groups(P<0.01),and the A90 keV group had the highest score.The scores of stent lumen in A70 keV group[(3.61±0.50)points]and B70 keV group[(3.47±0.63)points]were significantly better than other groups(P<0.01),and the score of A70 keV group was the highest.There was no significant difference in noise,CNR and AlN(F=1.67,0.15,1.16,P>0.05).The main effect analysis was energy level,there were significant differences in noise,CNR and AlN between groups a,B and conv(F=83.74,23.95,24.63,P<0.01).A70,80,90 keV group[(11.43±0.48),(11.81±0.34),(12.01±0.33)HU]and B70,80,90 keV group[(11.50±0.31),(11.58±0.18),(12.13±0.30)HU],image background noise was significantly lower than other groups(P<0.01).There was no significant difference between the six groups(P>0.05).The noise of A70 keV group was the least.The CNR in stent lumen of A50,60,70 keV groups(26.85±5.19,26.03±4.29,24.46±5.40)and B50,60,70 keV groups(25.88±5.67,24.18±5.46,24.91±7.67)was significantly higher than that of other groups(P<0.01).The highest CNR value was found in A50 keV group.The AlN value of A90,100,120 keV group[(32.22±6.16)%,(30.79±5.55)%,(27.05±4.47)%]was higher than that of conv group[(41.76±6.00)%],the difference was statistically significant(P<0.01).The AlN values of A90,100,120 keV group and B90,100,120 keV group[(34.34±5.73)%,(33.95±5.46)%,(33.92±5.45)%]were lower than those of other subgroups,and the differences were statistically significant(P<0.01).There was no statistically significant difference between the six groups(P>0.05).The AlN of A120 keV group was the lowest.Conclusions Regarding stent phantom imaging,DLCT monoenergetic imaging was better than conventional mixed energy imaging.When DLCT scanning was performed,90 keV(structure)and 70 keV(lumen)combined reconstruction could not reduce the imaging quality when the concentration was halved.