大范围低栅瓣锁定运动靶区的肝脏聚焦超声相控阵技术研究

Motion-suppression method with passive breath-hold is by far the most widely used in clinical studies of focused ultrasound liver surgery, albeit with treatment time lasting as long as several hours. And steering range of current phased arrays is insufficient to cover respiration-induced liver motion. Therefore, it is difficult to perform focused ultrasound liver surgery with motion track under free breathing. To overcome the above obstacles, spiral layout with wide range, low grating lobes (<-10dB) steering was designed for spherical phased arrays in this study. And sub-array beamforming was proposed to enlarge focal steering range. According to sparse random selection, the original spiral array was divided into several sub-arrays, each of which had its own center of curvature. The new spiral array composed of all sub-arrays was fabricated, based on which focused ultrasound phased array system was manufactured. A 3D motion device, which was used to control periodic motion of target, was developed to simulate liver motion under free breathing. Steering method with a focal point locked on target was proposed to track motion. Motion cycle was divided into several equal periods, at the beginning of which target position was obtained to update current focal point position. The focal point was then relocated dynamically and its acoustic intensity loss was compensated due to electronic beam steering. As a result, sonication with motion track was achieved in focused ultrasound liver surgery.

肝脏聚焦超声手术中普遍采用被动屏息的运动抑制方法使得治疗时间长达数小时。并且现有相控阵的偏转范围无法覆盖呼吸引起的肝脏运动范围，也使得难以实现自主呼吸下运动跟踪的肝脏聚焦超声手术。针对这些困难，本研究采用螺线球面阵设计来完成大范围的聚焦偏转，并使栅瓣水平低于-10dB。对此，本研究还提出了扩大偏转范围的子阵合成模式，结合稀疏随机阵设计将原螺线阵划分为若干独立的稀疏随机子阵，对应多个球面曲率中心，满足了覆盖肝脏靶区运动范围的要求，并搭建大范围低栅瓣螺线阵聚焦超声系统。为近似自主呼吸下肝脏运动，采用三维机械运动系统控制目标进行周期运动。提出锁定运动靶区的聚焦偏转方法，在靶区运动周期内分为数个等时间段，在每个时间段开始时获取靶区位置，并根据该信息更新当前焦点位置，进行焦点快速切换及声强补偿。从而在肝脏聚焦超声手术中实现运动跟踪的辐照消融。

肝脏聚焦超声手术中普遍采用被动屏息的运动抑制方法使得治疗时间长达数小时。并且现有相控阵的偏转范围无法覆盖呼吸引起的肝脏运动范围，也使得难以实现自主呼吸下运动跟踪的肝脏聚焦超声手术。已设计阵元数量分别为112和144且阵元呈环形分布的两个球面相控阵，将其应用于相控阵高强度聚焦超声系统，并对该系统进行超声声场分布的测量和离体组织的消融实验。采用旋转B超探头的方式在三维空间内跟踪运动靶区，并将B超图像内的靶区位置映射为相控阵焦点坐标，通过所搭建的相控阵超声驱动系统进行焦点位置的快速切换。其中，采用B超图像进行靶区定位的误差为1mm。已搭建一套三轴机械运动系统用于覆盖因呼吸运动引起的靶区运动范围。通过B超定位和相控阵高强度聚焦超声的技术融合，搭建了一套B超引导相控阵聚焦超声系统，通过活体兔及猪的动物实验完成了对运动靶区跟踪的可行性验证。此外，在所搭建B超引导系统中，采用基于双定向耦合器和功率检波的换能器驱动功率监测技术，实现对换能器加载功率的闭环反馈。针对所搭建的B超引导相控阵聚焦超声系统，已进行多项性能测试，其中，换能器的电-声转换效率约为50%，输出相位精度（负载端和功放端的平均误差分别为−0.3度和2.0度）和脉宽精度（平均误差为3.9%）都较高；相控阵可准确地聚焦偏转（焦点位置偏差约0.1mm），−6dB声场范围约为0.8mm×0.8mm×11.0mm，与理论结果（0.8mm×0.8mm×9.6mm）相当；B超定位的误差为1mm，满足了消融运动靶区的要求。同时，该系统具有驱动功率监测的功能，与商用功率计相比，功率监测值的误差在10%以内。