Research on Cross-Sectional Imaging of Elasticity around Atherosclerotic Plaque with Transcutaneous Ultrasound

相位跟踪方法的独特之处在于其极高的空间和时间分辨率。本文采用经皮超声相位跟踪法对动脉粥样硬化斑块周围的弹性进行了截面成像，可测速度最小值为0.5mm/s，积分时间间隔ΔT为222 μs。在此条件下，在使用水槽的测量中发现厚度变化的最低值约为0.1μm。这种微小的厚度变化是CT、MRI或标准超声诊断设备无法测量的，通过在心电图的R波处动脉壁中以375 μm的等间隔预先设置多个点，并对每个点应用上述方法，可以确定后续点之间每层厚度的变化。然后将每层厚度与R波厚度的变化转换为彩色图并显示。通过上述提出的过程，对人颈动脉的弹性模量E进行无创地评估，用于沿着超声束的五个层。通过修改上述方法和系统，使得通过控制超声束的位置来确定动脉壁和动脉粥样硬化斑块中的每个局部点的弹性模量。然后将结果转换成另一个彩色图，表示横截面图像中的局部弹性。在沿着动脉轴向的沿着30个位置处，在沿着超声波束的每个点处测量局部弹性。在深度方向和轴向方向的分辨率分别为375 μm和0.98 mm。动脉粥样硬化斑块的特点是内部的顺应性物质被许多弹性物质包围。通过外推体外研究的结果，我们将周围薄层解释为斑块的纤维帽。

The phased tracking method is unique in its extremely higher spatial and temporal resolution. This report shows the cross sectional image of the elasticity around the atherosclerotic plaque with this phase tracking method using transcutaneous ultrasound.The minimum value of the measurable velocity is 0.5 mm/s and the time interval, ΔT, of integration is 222 μs. In this condition, the lowest value of the change in thickness is found to be about 0.1μm in the measurements using a water tank. Such a minute change in thickness cannot be measured by CT, MRI, or standard ultrasonic diagnostic equipment.By presetting multiple points with equal intervals of 375 μm in the arterial wall at the R-wave of the ECG, and applying the above method to each point, the change in thickness in each layer between the succeeding points is determined. The change in thickness of each layer from that at the R-wave is then converted into color maps and displayed. By the proposed procedure described above, the elastic modulus E of the human carotid artery is noninvasively evaluated for the five layers along the ultrasonic beam.By modifying the method and system described above so that the elastic modulus of each local point in the arterial wall and the atherosclerotic plaque is determined by controlling the position of the ultrasonic beam. The results are then converted into another color map representing local elasticity in the cross sectional image. The regional elasticity is measured at each point along the ultrasonic beams at 30 positions along the axial direction of the artery. The resolution in the depth direction and axial direction is 375 μm and 0.98 mm, respectively. The atherosclerotic plaque has been characterized as the compliant material interior surrounded by much elastic material. With extrapolation of the results in an in vitro study, we interpreted the surrounding thin layer as the fibrous cap of the plaque.