基于单次时间反演求解的全颅骨声学透明化：经颅聚焦超声中基于互易性的换能器放置与孔径优化

中文摘要 AI 辅助

经颅聚焦超声受到颅骨的限制，颅骨的厚度、密度和曲率会以位置和目标依赖的方式使波束产生畸变和衰减，使得针对给定深部目标选择换能器耦合位置成为核心规划问题。本研究表明，单次全波时间反演求解即可解决该问题。目标处的虚拟点源通过CT颅骨模型向外辐射，根据声学互易性，时间反演场可同时给出颅骨表面每个点的发射耦合（即分块颅骨透明度图），并在同一次求解中获得任意阵列的逐阵元信号。对于相控阵，时间反演共轭了颅骨畸变，因此最优放置使递送能量最大化，该能量为孔径上的面积分；而单阵元则遵循将递送能量与相位相干性混合的相干评分，两种优化器会选择不同的窗口。随后，通过搜索这一单次记录的图谱，可在数秒内完成放置、孔径大小和方向的优化，无需对每个候选方案进行波求解。该图谱基于干颅骨微型CT模型，针对左侧齿状核，使用1 MHz非均匀Fullwave 2求解器，在每波长6.16个点并考虑骨衰减的条件下计算。一个120度枕部阵列在距齿状核0.25 mm内重新聚焦，每单位阵元驱动产生20.7 Pa；一个64 mm球面换能器置于递送能量最优的枕下窗口（距目标27 mm）时，以7.9倍增益重新聚焦；相同流程对丘脑的聚焦增益为15.2倍，对背侧前扣带回为11.4倍。畸变校正使目标处峰值压力比几何聚焦提高7.5倍（强度提高56倍），而几何聚焦会将焦点误导4.3 mm。同一场还测量了畸变的数毫米相干长度，该长度决定了所需的放置和目标定位精度。

英文摘要

Transcranial focused ultrasound is limited by the skull, whose thickness, density and curvature aberrate and attenuate the beam in a position- and target-dependent way, making the choice of where to couple a transducer for a given deep target a central planning problem. This work shows that a single full-wave time-reversal solve resolves it. A virtual point source at the target radiates outward through a CT skull model, and by acoustic reciprocity the time-reversed field gives the transmit coupling of every point on the skull surface at once (a per-patch skull transparency map) and, in the same pass, the per-element signals of any array. For a phased array, time reversal conjugates the skull aberration, so the optimal placement maximizes the delivered energy, a surface integral over the aperture; a single element instead follows a coherent score mixing delivered energy with phase coherence, and the two optimizers select different windows. Placement, aperture size and orientation are then optimized by searching this single recorded map in seconds, with no per-candidate wave solve. The map is computed on a dry-skull micro-CT model for the left dentate nucleus with a 1 MHz heterogeneous Fullwave 2 solver at 6.16 points per wavelength with bone attenuation. A 120 degree occipital array refocuses within 0.25 mm of the dentate at 20.7 Pa per 1 Pa of per-element drive, and a 64 mm spherical transducer seated in the delivered-energy-optimal suboccipital window (27 mm from the target) refocuses at 7.9x gain; the same procedure focuses the thalamus at 15.2x and the dorsal anterior cingulate at 11.4x. The aberration correction raises the on-target peak 7.5x in pressure (56x in intensity) over geometric focusing, which mis-steers the focus by 4.3 mm. The same field measures the aberration's few-millimeter coherence length, which sets the required placement and target-localization accuracy.

发表机构

• Lampe Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University（北卡罗来纳大学教堂山分校与北卡罗来纳州立大学联合兰佩生物医学工程系）

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