高分辨率空时自适应波控的HIFU损伤声辐射力剪切波粘弹性成像

The primary innovated research works of this project are related to the area of acoustic-radiation-force shear-wave imaging and will be listed as follows: Firstly, an innovation approach of spatio-temporal adaptive beamforming with time-reversal operation is proposed and will be established specifically for smaller focus dimension of impulse acoustic-radiation force to excite shear wave in complex inhomogeneous tissue for shear wave imaging. The adaptive approach can generate much higher shear wave amplitude, enhancing the signal-to-noise ratio and resolution, and deeper the imaging. The imaging process includes the ultrasound plane wave tracking displacement for the shear wave elastic imaging. We propose to develop a genetic algorithm in the adaptive control method as well. In addition, the optimal procedures will be taken in fully developed adaptive beamforming. Secondly, an imaging method consisted of two parallel-beam focus acoustic-radiation force for generating shear wave, is proposed, and will be investigated experimentally. The adaptive method will be involved in focal beamforming of acoustic radiation force. A k-space directional filter will be setup to remove the opposite direction shear wave induced from other focused beam. Thirdly, HIFU lesion is characterized quantitatively by using shear wave viscoelasticity imaging. The HIFU lesion property is investigated by using high-resolution ultrasound-shear-wave viscoelasticity imaging with adaptive method and acousto-optic imaging of shear wave. In addition, the dynamic HIFU-lesion property in vitro or in vivo will be investigated using shear wave viscoelasticity imaging. To get rid of the influence from cavitation remnants, the protocol of inserting a short-period-time ultrasound pressure incident after therapy can be effective to destroy the cavitation nuclei. The aim of this study is to establish an effective HIFU monitoring method. As a result, the formation of these imaging methods in this research will be of great value in shear wave imaging method and technology and imaging application as well.

本项目在声辐射力剪切波成像方法和应用方面展开前沿研究，主要研究：(1)提出并建立非均匀组织中时间反演自适应波控小径向尺寸焦点脉冲辐射力激励剪切波成像控制方法，此方法能提高剪切波幅、信噪比和成像分辨率并增加成像深度，同时方法中以超声平面波跟踪估计剪切波位移进行成像；自适应方法中构建遗传优化算法；进一步建立最优参数自适应波控。(2)提出和建立双平行波束同时焦点的辐射力剪切波激励方式，提高剪切波成像速度，双平行波束采用自适应波控，配以k波滤波器消除另一平行波束反方向剪切波的影响。(3)采用自适应波控的高分辨率超声剪切波粘弹性成像和声光剪切波粘弹性成像进行HIFU损伤的实验研究; 对损伤动态过程粘弹性成像，配以治疗后即时湮灭空化核策略，建立准确判定损伤的监控方法。项目的提高剪切波成像分辨率和速度的创新方法研究以及HIFU实时监控应用的突破性研究具有重要学术和应用价值。

项目在国际前沿研究领域展开了创新性方法探索；研究内容定位为定量粘弹特性、高精度辐射力剪切波控成像方法和其在HIFU监控中应用方面的研究; 本项目的研究具有重要的学术和应用意义。.项目按研究计划①首先研究了脉冲响应的表面波粘弹性参数测量估计：基于改进的Voigt 模型得到时域脉冲响应的阻尼比和弹性相关参数，进而以此两个参数分析热损伤分布的粘弹性。 ②进一步项目重点研究了脉冲声辐射力剪切波在深部组织中定量粘弹性方法：在对不同脉宽响应法、频率抽取法、位置响应衰减分析法的深入研究基础上，最终在k-空间方法方面获得定量粘弹性获取的突破，由k-空间峰值频率定量剪切波速度，由k-空间半高宽得到与粘性相关的定量声衰减系数，最后由Voigt关系定量得到剪切弹性模量μ1和剪切粘性μ2。③项目重点开展了时间反演优化声辐射力焦点激励研究；主要针对声辐射力在复杂介质激励条件，为获得聚焦尺寸小、峰值高和聚焦深度深而进行的优化控制；具体用相控阵获得时间反演算子的透射-反射阵进行相位校正，进一步用测得的透射-反射阵以能量最大的自适应聚焦方法驱动聚焦；可获得聚焦幅度提升2倍和声压半高宽减少一半的优化激励效果。④项目重点开展了高精度剪切波跟踪成像方法的研究；研究了超快相干平面波并行波束剪切波跟踪复合成像方法和高精度超声多相干平面波复合成像方法；研究了剪切波脉冲响应的剪切群速度估计的空时峰值法（Spatiotemporal, STP）。项目将超声相干平面复合成像结合超快速空化成像方法应用于HIFU治疗的空化域监控中。⑤项目还研究了光流法声辐射力剪切波成像方法：用金字塔结合LK光流法获得高精度剪切波成像。⑥项目研究了声辐射力剪切波调制的光学散斑的声光成像方法；在剪切波的光相位增量模型基础上，采用Monte Carlo模型仿真了剪切波调制光的机理，估计出了剪切波速。⑦最后，项目用激光测振获得的声辐射力剪切波速和得到的剪切弹性实时监控HIFU组织毁损两阶段治疗过程；这种监控已辅助用于揭示治疗的物理机制。.