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目的 与传统探测器对比,探讨光子探测器对低电压大螺距双能量头颈部CT血管成像(CTA)迭代重建(IR)图像质量的影响.方法 对2012年12月至2013年1月,连续性50例临床诊断或怀疑头颈部动脉血管疾病的患者进行双能量头颈部CTA检查.采用随机表格为患者抽签,将患者分至2组:A组(24例)使用Stellar光子探测器,B组(26例)用传统探测器.CT扫描采用2台128层双源FLASH CT扫描仪,分别具有传统探测器及Stellar光子探测器.采用双筒高压注射器,首先采用小剂量团注测试计算扫描延迟时间.随后进行CTA检查,注入对比剂40 ml及生理盐水48 ml,注射流率为6 ml/s.采用低能量管电压组合(A、BX线管电压分别为140、80 kVp),准直2×64×0.6 mm,采用Z轴飞焦点技术,螺距1.2.重建层厚1.0 mm.双源组合因子0.6.采用SAFIRE迭代重建进行图像后处理.每例患者得到3组IR增强图像,分别为140 kVp SAFIRE、80 kVp SAFIRE、融合图像(相当于100 kVp)SAFIRE.记录辐射剂量,包括容积CT剂量指数(CTDIvo1)和剂量长度乘积(DLP),并计算有效剂量(ED).测量2组患者各组IR序列1.00 mm轴面增强多平面重组(MPR)图像以下3个层面的各项数据:(1)主动脉弓(AA)水平,胸廓的最大前后径(R1前后),AA的CT值及SD值;(2)颈总动脉(CCA)分叉水平,颈部最大前后径(R2前后)及最大左右径(R2左右),对比剂注射对侧的CCA、胸锁乳突肌(SCM)、颈部腹侧空气的CT值及SD值;(3)颈内动脉床突段(C5)水平,头颅的最大前后径(R3前后)及最大左右径(R3左右),C5及脑干的CT值及SD值.计算AA、CCA及C5的对比噪声比(CNR).由2名医师进行定性评价,得出一致性结论.采用4分法分别对2组患者各组IR序列图像上的脑组织噪声、蛛网膜下腔边缘的清晰程度、灰白质分界的清晰程度以及大脑中动脉(MCA)显示情况进行评分.采用t检验、Wilcoxon非参数检验及Mann-Whitney U非参数秩和检验的方法,对组间所得数据的进行比较.结果 2组患者的ED差异无统计学意义(t=0.93,P=0.35),A组CTDIvol为(3.85±0.17) mGy,高于B组(3.74±0.18) mGy,差异具有统计学意义(t=2.17,P=0.03).A组患者140 kVp IR重建的主动脉及颈内动脉SD值[(25.8±4.3)、(17.7±7.4) HU]均高于B组[(22.8±3.6)、(13.6±5.7)HU)],差异具有统计学意义(t值分别为2.73、2.24,P值分别为0.01、0.03).A组患者140 kVp IR、80kVp IR、融合图像IR脑干的SD值分别为(17.1±2.6)、21.0(19.4,22.70)、14.8(13.4,16.4) HU,均低于B组患者[(18.7±2.3)、24.8(21.6,26.8)、16.6(14.9,18.5) HU)],差异具有统计学意义(t=-2.30,P=0.03; Z=-3.18,P=0.01;Z=-2.34,P=0.02).2组不同重建方法的各能量序列之间定性评分比较差异均无统计学意义(P＞0.05).结论 Stellar光子探测器进行低电压大螺距的双能量头颈CTA检查,采用IR重建方法,与普通探测器相比,有效剂量无显著差异,但Stellar光子探测器可以降低脑组织噪声.

Objective To detect the image quality of dual-energy CT angiography(CTA) of head and neck arteries with low tube voltage,high pitch and iterative reconstruction(IR) using photon detectors,compared with conventional detectors.Methods CTA of the head and neck arteries was performed on 50 consecutive patients with suspected or previously diagnosed arterial diseases of head and neck.Patients were randomized to one of two groups using stellar photon detectors(Group A,n=24) or conventional detectors (Group B,n=26).CTA was performed with two 128-slice dual source CT systems with photon detectors and conventional detectors,respectively.Dual-enery low tube voltage settings were 140 kVp/80 kVp in tube A/B,and a high pitch of 1.2.All acquisitions were reconstructed with IR,1.0 mm thickness,DE composition=0.6.CTDIvol(CT dose index volume) and DLP(dose-length product) were recorded.Effective dose(ED) was calculated.Quantitative measurements were performed on each IR sequence(140kVp,80kVp and mixed energy) of 1.00 mm enhanced MPR(multi planar reformations) images as follows:(1) on the level of aortic artery(AA),the largest anteroposterior diameter of chest(R 1AP),CT attenuation values and standard deviation (SD) of AA; (2) on the level of common carotid artery(CCA) bifurcation,the largest auteroposterior and leftright diameter(R2AP,R2LR),CT attenuation values and SD of CCA,sternocleidomastoid muscle(SCM),ventral air of the neck on the contralateral side of contrast injection; (3) on the level of the clinoid segment of internal carotid artery(C5),the largest anteroposterior and left-right diameter(R3AP,R3LR),CT attenuation values and SD of C5 and brain stem.CNR of AA,CCA and C5 calculated as CNR.Qualitative assessments for each IR images were based on:noise of brain parenchyma,sharpness of subarachnoid space margins,grey matter-white matter differentiation and the visualization of middle cerebral arteries.t test,Wilcoxon nonparametric test and Mann-Whitney U test were used to compare the difference between the two groups.Results There was no significant difference in ED between group A and B(t=0.93,P=0.35),CTDIvol was higher in Group A(3.85 ±0.17) mGy,compared with Group B(3.74±0.18) mGy(t=2.17,P=0.03).The SD of AA and CCA of 140 kVp IR images of Group A[(25.8±4.3),(17.7±7.4) HU] were higher than that of Group B [(22.8 ± 3.6),(13.6 ± 5.7) HU].The difference indicated statistical significance(t=2.73,P=0.01 ; t=2.24,P=0.03).The SD of brain stem of 140 kVp IR,80 kVp IR and mixed-energy IR image of Group A were(17.1± 2.6),21.0(19.4,22.7) and 14.8(13.4,16.4) HU,and were lower than that of Group B(18.7±2.3),24.8(21.6,26.8),16.6(14.9,18.5) HU.The difference indicated statistical significance(t=-2.30,P=0.03;Z=-3.18,P=0.01 ;Z=-2.34,P=0.02).There was no significant difference in qualitative assessments of each IR images between the two groups(P＞0.05).Conclusions Stellar photon detectors results in lower noise of brain stem and dose not increase effective dose in low-tube-voltage and high-pitch DE CTA of head and neck,with IR reconstraction method,compared with conventional detectors.