Department of Bioengineering, Stanford University, Stanford, CA, USA.
Focused Ultrasound Foundation, Charlottesville, VA, USA.
Sci Rep. 2021 Mar 22;11(1):6532. doi: 10.1038/s41598-021-85535-5.
The InSightec Exablate system is the standard of care used for transcranial focused ultrasound ablation treatments in the United States. The system calculates phase corrections that account for aberrations caused by the human skull. This work investigates whether skull aberration correction can be improved by comparing the standard of care InSightec ray tracing method with the hybrid angular spectrum (HAS) method and the gold standard hydrophone method. Three degassed ex vivo human skulls were sonicated with a 670 kHz hemispherical phased array transducer (InSightec Exablate 4000). Phase corrections were calculated using four different methods (straight ray tracing, InSightec ray tracing, HAS, and hydrophone) and were used to drive the transducer. 3D raster scans of the beam profiles were acquired using a hydrophone mounted on a 3-axis positioner system. Focal spots were evaluated using six metrics: pressure at the target, peak pressure, intensity at the target, peak intensity, positioning error, and focal spot volume. For three skulls, the InSightec ray tracing method achieved 52 ± 21% normalized target intensity (normalized to hydrophone), 76 ± 17% normalized peak intensity, and 0.72 ± 0.47 mm positioning error. The HAS method achieved 74 ± 9% normalized target intensity, 81 ± 9% normalized peak intensity, and 0.35 ± 0.09 mm positioning error. The InSightec-to-HAS improvement in focal spot targeting provides promise in improving treatment outcomes. These improvements to skull aberration correction are also highly relevant for the applications of focused ultrasound neuromodulation and blood brain barrier opening, which are currently being translated for human use.
Insightec 的 Exablate 系统是美国经颅聚焦超声消融治疗的标准治疗方法。该系统计算相位校正，以弥补颅骨引起的像差。这项工作通过比较标准的 Insightec 光线追踪方法与混合角谱（HAS）方法和金标准水听器方法，研究了颅骨像差校正是否可以得到改善。三个脱气的离体人头骨用 670 kHz 半球形相控阵换能器（Insightec Exablate 4000）进行了超声处理。使用四种不同的方法（直线光线追踪、Insightec 光线追踪、HAS 和水听器）计算相位校正，并用于驱动换能器。使用安装在三轴定位系统上的水听器获得了光束轮廓的 3D 光栅扫描。使用六个指标评估焦点：目标处的压力、峰值压力、目标处的强度、峰值强度、定位误差和焦点体积。对于三个头骨，Insightec 光线追踪方法实现了 52 ± 21%的归一化目标强度（相对于水听器归一化）、76 ± 17%的归一化峰值强度和 0.72 ± 0.47 mm 的定位误差。HAS 方法实现了 74 ± 9%的归一化目标强度、81 ± 9%的归一化峰值强度和 0.35 ± 0.09 mm 的定位误差。在焦点定位方面，Insightec 到 HAS 的改进有望改善治疗效果。这些对颅骨像差校正的改进对于聚焦超声神经调节和血脑屏障开放的应用也非常重要，目前正在为人体应用进行转化。
