Vulnerable Plaque Detection with Carotid Strain Imaging

描述（由申请人提供）：目前治疗动脉粥样硬化斑块或动脉粥样硬化的临床标准主要集中在血管狭窄的百分比上。然而，狭窄的百分比并不能识别容易破裂的斑块，这可能会将栓子释放到敏感的脑血管的血流中。这些“脆弱”的斑块特别容易产生突发的重大问题，比如心脏病发作或中风。如果动脉粥样硬化生长迅速，并且只有一层薄薄的纤维帽将软脂池和其他斑块成分与血液分开，那么动脉粥样硬化就会变得脆弱。颈动脉斑块的结构稳定性是其化学成分、细胞材料和新血管形成的结果。各种研究表明，血流引起的脉动压力可能使覆盖在富含脂质病变上的薄帽破裂，导致随后的血栓形成和斑块破裂。因此，斑块易损性主要由血管壁和斑块组成的机械（弹性）特性决定。超声应变成像可以提供一种识别易损斑块的方法。一种新的应变成像方法，即通过颈动脉的血液脉动来诱导组织位移进行应变成像，将被开发和评估。我们建议使用三个“应变指标”，即；最大累积轴向应变，最大横向位移和应变，剪切应变斑块在心脏周期的脆弱性措施。为了获得法向和剪切应变张量，我们建议利用沿不同角度失谐方向获得的波束控制射频数据来计算位移矢量，进而计算应变张量。我们还将采用一种改进的动态二维多层次互相关方法来跟踪局部位移与获得的角度数据。我们的初步结果证明了无创区分软斑块和硬斑块的能力。长期目标是为斑块破裂风险患者提供一种无创测量方法，扩展目前基于局灶性短暂性脑缺血发作或中风的动脉粥样硬化风险治疗标准。在有限的患者体内研究中，将对年龄匹配的对照组志愿者进行类似的分析，以确定“应变指数”对易损斑块识别的重要性。最后，在颈动脉内膜切除术后，整个切除的斑块核心将在相同的体内横截面（基于血流分割器的测量）上进行组织学分析，进一步评估，其中进行应变成像以更好地了解斑块的组成和结构（以及微生成和新生血管），以显示正常和剪切应变图像上的信息。

DESCRIPTION (provided by applicant): Current clinical criteria for treatment of atherosclerotic plaque or atheromas, has focused primarily on percent stenosis of the vessel. However, percent stenosis does not identify plaque prone to rupture that may release emboli into the blood stream of the sensitive cerebral vasculature. These 'vulnerable' plaques are particularly prone to produce sudden major problems, such as a heart attack or stroke. Atheromas become vulnerable if they grow rapidly and have only a thin fibrous cap separating the soft lipid pool and other plaque constituents from the bloodstream. Structural stability of carotid plaque is a result of its chemical composition, cellular material and new vessel formation. Various studies have indicated that pulsatile pressure induced due to blood flow may rupture the thin cap overlying lipid rich lesions, leading to subsequent thrombosis and plaque rupture. Plaque vulnerability is therefore determined primarily by the mechanical (elastic) properties of the vessel wall and plaque composition. Ultrasound-based strain imaging can provide a means of identifying vulnerable plaque. A novel approach to strain imaging, where pulsation of blood through the carotid artery is used to induce tissue displacements for strain imaging, will be developed and evaluated. We propose the use of three 'strain indices' namely; maximum accumulated axial strain, maximum lateral displacement and strain, and shear strains in plaque over the cardiac cycle as measures of plaque vulnerability. To obtain the normal and shear strain tensors, we propose to utilize beam-steered radiofrequency data acquired along different angular insonification directions to compute the displacement vectors and subsequently the strain tensors. We will also incorporate a modified dynamic 2D multi-level cross-correlation method to track local displacements with the angular data acquired. Our preliminary results demonstrate the ability to differentiate between soft and stiffer plaque noninvasively. The long term objectives are to provide a non-invasive measurement of patients at risk for plaque rupture, expanding upon the current criteria for treatment for atherosclerotic risk based on focal transient ischemic attacks or strokes. The limited in-vivo study on patients will be complimented by a similar analysis on a control group of age-matched volunteers to determine the significance of the 'strain indices' for discrimination of vulnerable plaque. Finally, the entire excised plaque core following carotid endarterectomy will be further evaluated using histological analysis at the same in-vivo transverse cross-sections (based on measurements from the flow- divider) where strain imaging was performed to better understand plaque composition and structure (along with microulcerations and neovascularity) to the information displayed on the normal and shear strain images. PUBLIC HEALTH RELEVANCE: Ultrasound-based strain imaging can provide a means of identifying vulnerable plaque. A novel approach to strain imaging, where pulsation of blood through the carotid artery is used to induce tissue displacements for strain imaging, will be developed and evaluated. One of the goals of this research is to help determine patients at risk for stroke, while excluding patients with manageable risk from undergoing surgery, both of which would dramatically reduce healthcare costs.