Assessment of Intracranial Arterial Stenosis with Multidetector Row CT Angiography: A Postprocessing Techniques Comparison

L. Saba; R. Sanfilippo; R. Montisci; G. Mallarini

摘要

BACKGROUND AND PURPOSE: It was demonstrated the some patients with stroke have intracranial stenosis of 50% or greater and the identification of intracranial arterial stenosis is extremely important in order to plan a correct therapeutical approach. The aim of this study was to assess the image quality and intertechnique agreement of various postprocessing methods in the detection of intracranial arterial stenosis. MATERIAL AND METHODS: Eighty-five patients who were studied by using a multidetector row CT scanner were retrospectively analyzed. A total of 2040 segments were examined in the 85 subjects. Intracranial vasculature was assessed by using MPR, CPR, MIP, and VR techniques. Two radiologists reviewed the CT images independently. Cohen weighted statistic was applied to calculate interobserver agreement and for image accuracy for each reconstruction method. Sensitivity, specificity, PPV, and NPV were also calculated by using the consensus read as the reference. RESULTS: Two hundred fifteen (10.5%) stenosed artery segments were identified by the observers in consensus. The best intermethod values between observers 1 and 2 were obtained by VR and MIP ( values of 0.878 and 0.861, respectively), whereas MPR provided the lowest value ( value of 0.282). VR showed a sensitivity for detecting stenosed segments of 88.8% and 91.6% for observers 1 and 2, respectively. The highest positive predictive value was also obtained by VR at 95% and 99% for observers 1 and 2, respectively. Image accuracy obtained by using VR was the highest among all reconstruction methods in both observers (185/255 and 177/255 for observers 1 and 2, respectively). CONCLUSIONS: The results of our study suggest that VR and MIP techniques provide the best interobserver and intertechnique concordance in the analysis of intravascular cranial stenosis. Abbreviations: CPR, curved planar reconstruction • CTA, CT angiography • DSA, digital subtraction angiography • HU, Hounsfield unit • ICA, internal carotid artery • MDCTA, multidetector row CT angiography • MIP, maximum intensity projection • MPR, multiplanar reconstruction • MRA, MR angiography • NASCET, North American Symptomatic Carotid Endarterectomy Trial • NC, not calculated • NPV, negative predictive value • PPV, positive predictive value • VR, volume rendering Stroke is the third leading cause of mortality and the leading cause of morbidity in the United States and it is usually determined by extracranial carotid pathology.1–3 In fact, it has been demonstrated that some patients with stroke show intracranial stenosis of 50% or greater4 and that the identification and characterization of intracranial arterial stenosis is extremely important to plan the correct therapeutic approach. DSA has long been considered the criterion standard for imaging evaluation of intracranial stenosis and occlusion even if MDCTA and MRA have been increasingly used as feasible noninvasive techniques to evaluate the intracranial vasculature. In particular, the ongoing development of MDCTA technology has transformed CT into a 3D imaging technique with outstanding temporal and spatial resolution and the capacity for visualization of even millimeter-sized vessels such as the Adamkiewicz artery.5,6 By using MDCT, it is possible to employ different postprocessing techniques in addition to source axial images. MIP, MPR, CPR, and VR7,8 are currently the most frequently used. A deeper knowledge of the potential of postprocessing techniques and their application will allow optimization of the MDCTA dataset. To the best of our knowledge no previous studies have compared these tools for the assessement of intracranial vasculature. The purpose of this study was to assess the image quality and intertechnique agreement of different MDCTA postprocessing techniques in the analysis of intracranial arterial stenosis. Materials and Methods Patient Population The study group was selected following a search in the patient database of the Azienda Ospedaliero–Universitaria di Cagliari, Polo di Monserrato (previously Policlinico Universitario di Monserrato). Study patients were enrolled from those subjects who had undergone a previous CTA for the study of supra-aortic vessel and intracranial vasculature from January 2007 to June 2008. The study cohort included 85 patients (67 men, 18 women; mean age, 68 years; age range, 49–86 years) who had been studied by using a multidetector row CT scanner. This is a retrospective study, and each MDCTA examination was performed when it was clinically indicated, and it was ordered by the patient's physician as part of routine clinical care. In our institute, the inclusion criterion for performing MDCTA is as follows: a prior given clinical indication for CT angiography of the supra-aortic vessels (when possible also confirmed by ultrasound echo color Doppler study) as stated by the referring physician and established by the attending radiologist. In particular, the main reason for referral to MDCTA is a sonography (ultrasound) examination that showed a pathologic stenosis and/or a plaque alteration or when ultrasound cannot provide sufficient information about the degree of stenosis, as for example in the presence of large calcified plaques with acoustic shadowing, high carotid bifurcation, or hostile neck (edema, obese patients). Plaque alteration was considered as the presence of a heterogeneous plaque, an irregular surface, intraplaque hemorrhage, and/or the presence of ulceration in the plaque. Carotid arteries of asymptomatic patients were studied in our department in diabetics 10 years of experience in vascular study). Cases were presented in a random order, and both observers were blinded to the patient history and to all clinical information. To prevent recall bias risk, different postprocessed images from the same patient were presented to the readers separately; first, all MPR postprocessed images were analyzed, followed by VRs, CPRs, and MIPs, respectively. While evaluating the individual postprocessed dataset, readers did not have access to the source images. In the evaluation of all imaging modalities, the NASCET criteria were used for stenosis calculations, as previously reported13: [(D_n – D_s)/D_n] x 100, where D_n is normal diameter and D_s is stenosed diameter. We considered the vessel distal to the stenosis as normal for stenosis. NASCET stenoses were grouped according to the following grading scale9: normal (0%–9%), mild (10%–29%), moderate (30%–69%), severe (70%–99%), or occluded, and diseased vessels were defined as those whose NASCET stenosis rates fell into the moderate, severe, or occluded categories.13 The following bilateral arterial segments were included13: high cervical ICA, petrous ICA, cavernous ICA, supraclinoid ICA, A1, A2, M1, M2, intracranial vertebral, P1, and P2, as well as the proximal basilar and distal basilar arteries. Therefore, a total of 2040 vessel segments were examined in the 85 subjects. When an intracranial artery was uniformly and segmentally of decreased caliber throughout its length when compared with the contralateral side, this vessel segment was considered hypoplastic and no stenosis was attributed.13 After the independent reading of the CTA dataset, observers reanalyzed data in consensus by using axial CTA images and postprocessing procedures to develop a reference standard. Both of the observers discussed each CTA dataset 1 month after their independent analysis and in the case of discrepant opinion, new measurements were reobtained by considering the axial CTA images and the postprocessing procedures. The observers classified the quality of the 4 postprocessed datasets in each patient by grouping them into 4 categories: poor, suboptimal for diagnostic purposes (0); fair, only adequate for diagnostic purposes (1); good but slightly lower quality compared with excellent, but useful for diagnostic purposes (2); and excellent, high quality for diagnostic purposes (3). In the final phase we measured the HU value in each ICA and we correlated this value with the quality image. To calculate the HU value each reader measured the HU values in the high cervical ICA by using a circular or elliptical region-of-interest cursor. HU opacification was then classified according to 3 categories: >400 HU, >250 to 400 HU) should be pursued to achieve optimal image quality. View this table: [in this window] [in a new window] Table 7: Observer 2 quality image evaluation for each patient by comparing various reconstruction methods

机译：背景与目的：已证明部分脑卒中患者的颅内狭窄≥50％，对颅内动脉狭窄的鉴别对于计划 Sup> 动脉狭窄至关重要。 sup> 正确的治疗方法。这项研究的目的是评估各种后处理方法在颅内动脉狭窄检测中的图像质量和技术间的一致性。材料与方法：回顾性分析了使用多排行CT扫描仪研究的85例患者。在85位受试者中共检查了2040个段。使用MPR，CPR，MIP和VR技术评估了颅内脉管系统。两名放射科医生独立检查了CT图像。应用Cohen加权统计量来计算观察者之间的一致性以及每种重建方法的图像准确性。还使用共识作为参考来计算灵敏度，特异性，PPV和NPV。结果：215（10.5％）观察者一致地确定狭窄的动脉节段。观察者1和观察者2之间的最佳方法间值是通过VR和MIP获得的（值分别为0.878和0.861），而MPR提供了最低值（值0.282）。 VR对观察者 1和2的检测狭窄段的敏感性分别为88.8％和91.6％。 VR也分别为观察者1和2分别以95％和99％的比例获得了最高的阳性预测值。在两个观察者中，使用VR获得的图像准确性在所有重建方法中最高（（观察者1和2分别为185/255 和177/255）。结论：我们的研究结果表明，VR和MIP技术在分析颅内血管狭窄方面提供了最佳的观察者间和技术间的一致性。 / sup>缩写：CPR，弯曲平面重建•CTA，CT血管造影•DSA，数字减影血管造影•HU，Hounsfield单位•ICA，颈内动脉•MDCTA，多探测器行CT血管造影•MIP，最大强度投影•MPR，多平面重建•MRA，MR血管造影术•NASCET，北美有症状颈动脉内膜切除术试验•NC，未计算•NPV，阴性预测值•PPV，阳性预测值•VR，容积渲染卒中是导致死亡的第三大原因，也是主要原因美国统计中的发病原因es，通常由颅外颈动脉病变确定。 1-3 实际上，它已经证明表明某些中风患者表现为颅内< sup> 狭窄率为50％或更高的 4 ，并且颅内动脉狭窄的识别和特征非常重要，正确的治疗方法。即使已经越来越多地使用MDCTA 和MRA，长期以来，DSA也一直被认为是评估颅内狭窄和闭塞的影像学的标准标准。可行的非侵入性技术来评估颅内血管系统。特别是 MDCTA技术的不断发展已将 CT转换为具有出色的时间和空间分辨率以及可视化显示能力的3D成像技术。甚至毫米大小的血管，例如Adamkiewicz动脉。 5,6 通过使用MDCT，可以采用不同的后处理 < / sup>技术，以及源轴向图像。 MIP，MPR，CPR，和VR 7,8 当前是最常用的。对后处理技术的潜力及其应用有更深入的了解将允许优化MDCTA数据集。据我们所知，以前没有研究将这些工具用于评估颅内血管系统。在颅内动脉狭窄分析中，不同MDCTA后处理技术的图像质量和技术一致性。材料和方法患者人群本研究组的选择如下在Azienda Ospedaliero–Cagliari大学的Patient 数据库中进行搜索， Polo di Monserrato（以前为Policlinico Universitario di Monserrato）。研究对象来自2007年1月至6月间曾接受过CTA研究的主动脉上血管和颅内血管系统的受试者 2008。该研究队列包括使用多探测器行对进行研究的85名患者（67名男性，18名女性；平均年龄，68岁；年龄范围，49-86岁）。 CT扫描仪。这是一项回顾性研究，每次MDCTA检查均在临床指征时进行，并且由患者的医师下达了的要求。作为常规临床护理的一部分。在我们研究所，进行MDCTA 的纳入标准如下：CT血管造影的既往临床指征由主诊放射科医师陈述并由主治放射科医生确定的主动脉上血管的数量（如果可能，还应通过超声波回波彩色多普勒研究确认）。特别是，转到MDCTA的主要原因是超声检查（超声）检查显示病理狭窄和/或斑块改变或当超声不能提供足够的有关狭窄程度的信息时，例如在存在声影阴影的大钙化斑块，高颈动脉分叉的情况下存在大钙化斑块的情况下（sup> ）或敌对的脖子（水肿，肥胖患者）。斑块改变被认为是存在异质斑块，表面不规则，斑块内出血和/或斑块中存在溃疡。在我们的科室，研究的冠状动脉疾病，主动脉的患者干预措施和下肢动脉手术。研究的排除标准包括对碘化造影剂的禁忌症，例如对碘化碘的已知过敏< sup> 对比材料，或肾功能检查升高。因为这项研究是回顾性的，并且进行的成像与本组例行的常规检查没有区别。 > 患者，根据我们部门研究委员会的政策，本研究不需要特定的伦理学批准。我们的一些患者也包括在内在以前的研究中被盲目的用于同行评审。 MDCTA颈动脉检查的研究是使用4-探测器行CT扫描仪（Philips MX8000;以前是Picker（位于马萨诸塞州安多佛）。在接收到有关检查类型的信息后，要求每位患者签署知情同意书以进行造影剂管理。将患者置于仰卧位，头部向后倾斜可以防止图像上出现牙齿伪影，并且沿着胸部。还指示患者不要呼吸和不要吞咽。获取了包括胸部，颈部和头骨的侦察视图。 CTA扫描范围包括升至主动脉至颅内血管（蝶鞍上方5 cm处），因为在我们的中部头颈CTAs通常为结合。静脉注射90-140 mL造影剂（Ultravist 370；先灵，柏林，德国）以4-6 mL / s，使用动力注射器并在肘前静脉中插入18至20规格的静脉内导管。延迟时间变量从12到施加18秒。通过在caudocranial 扫描方向上进行螺旋采集获得图像，切片厚度为1.3 mm，的增量为0.6毫米，矩阵为512 x 512，视场角为16–19 cm （260–300 mAs； 120–140 kV）。后处理方法工作站（Philips Dell Precision 690，Intel Xeon处理器）通过使用MPR，MIP，CPR和VR算法（图1）。 MPR可能是最简单且最常用的格式化方法，它包括获得沿投影轴的像素衰减的平均值。血管MPR图像是2D图像，因此无法分析血管走向。 9 每个数据集的多个投影自由生成的，放射科医生可以操作窗口，中心，以及视角。查看大图（52K）：[在此窗口中] [在新窗口中]图1. 63岁的女性患者：后处理的VR（A）， MIP（B），电晕MPR（C）和CPR图像（D，E）。 CPR描绘了沿其长度的血管的横截面轮廓，同时保留了相对的X射线衰减。在每个图像上通过一系列连续的源图像，通过一系列鼠标单击来跟踪目标血管的走向。 10 此过程将一直持续到跟踪到整个容器。 CPR非常耗时，与真实中心线的微小偏差，特别是在狭窄的动脉中，会产生假性狭窄，或者相反，会导致重要的 VR是可用的最先进的计算机密集型渲染算法之一，将所有相关数据整合到生成的图像，并生成高质量的3D血管造影图像。通过选择相对于体素强度直方图的相对的梯形生成VR图像，然后指定不透明度值定义其相对透明度。为了去除骨骼，我们使用了两个不同的步骤：自动去除骨骼功能，然后是手动切割功能。设置了自动骨骼去除功能，以仅排除与所选目标最接近的的体素，以避免可能会切断血管的结构；为了完成非自动骨骼去除的区域，我们使用专用的软件手动删除了骨骼。然后保存了具有骨骼去除的数据集用于 MIP分析中，使MIP不重叠骨骼。 MIP是一个简单的3D可视化工具，可用于显示 CTA数据集。 MIP图像与阈值无关，它们保留整个CT数据集。对于给定的观看方向，平行射线投射通过感兴趣的体积，并显示沿每个射线遇到的最大CT数。由于的原因，如果在投影射线中发现了骨骼或钙化，这些结构将显示在MIP图像上，而不是增强造影剂的血管中 9 因为衰减值更高，这可能代表了该技术的最大缺点。读者可以使用MIP厚板，厚度可自由修改。此外，从 VR分析获得的CT VR骨骼排斥被用于生成MIP图像，而没有已经被移除的骨骼结构的体素。图像分析由2位独立观察员（观察员1，具有5年血管研究经验的放射科医生）对MDCTA图像进行了狭窄的存在，位置和严重程度的审查。 ; observer 2，一位在血管研究中有10年以上经验的放射科医生）。病例以随机顺序出现，两位观察者都不了解患者病史和所有临床信息。为防止召回偏倚风险，将来自同一患者的不同后处理图像分别呈现给读者；首先，分析所有MPR后处理图像，然后分别分析VR，CPR和MIP。在评估各个后处理数据集时，读者 did不能访问源图像。在评估所有成像方式时，如先前报道的 13 ，将NASCET标准用于狭窄计算。： [（D _{n – D _{s ）/ D _{n ] x 100，其中D _{n 是正常直径， D _{s 是狭窄直径。我们认为狭窄的血管是狭窄的正常情况。 NASCET狭窄根据以下等级进行分类： scale 9 ：正常（0％–9％），轻度（10％–29％），中度（30％–69％），严重（70％–99％）或闭塞，以及患病的血管的定义是那些NASCET狭窄率分为中度，严重或闭塞的血管。 13 包括以下 13 的双侧动脉节段：高子宫颈ICA，岩性ICA，海绵状ICA，蛛网膜ICA， A1，A2，M1，M2 ，颅内椎，P1和P2，以及基底基底动脉和基底基底动脉的。因此，在85位受试者中共检查了2040个血管段。当的颅内动脉均匀且分段减小口径时，与对侧相比，该血管段被认为是增生性的，没有狭窄的原因。 13 读取CTA数据集后，观察者通过使用轴向CTA图像和后处理程序重新分析了数据，以制定参考标准。两名观察员在独立分析 1个月后讨论了每个CTA数据集，并且在意见不一致的情况下，通过考虑以下因素重新获得了新的测量值。轴向CTA图像和后处理程序。观察者将每个患者的4个后处理数据集的质量分为4类： sup> 差，出于诊断目的而欠佳（0）;公平，仅足够用于诊断目的的（1）;良好，但质量稍低，与之相比，优良，但对于诊断目的有用（2）以及用于诊断目的的卓越，高质量（3）。在最后阶段，我们测量了每个ICA的HU值，并且将这个值与质量图像相关联。为了计算 HU值，每个阅读器通过使用圆形或椭圆形感兴趣区域光标测量了高子宫颈ICA中的HU值。然后根据3 类别对HU遮光进行分类：应追求> 400 HU，> 250到400 HU）以获得最佳图像质量。 < sup> 查看此表：[在此窗口中] [在新窗口中]表7：通过比较各种重建方法，对每个患者的观察者2质量图像评估}}}}}

Assessment of Intracranial Arterial Stenosis with Multidetector Row CT Angiography: A Postprocessing Techniques Comparison

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