Graduate Program in Acoustics, The Pennsylvania State University, University Park, PA, United States of America.
Phys Med Biol. 2023 Jan 5;68(2). doi: 10.1088/1361-6560/aca9b7.
High-intensity focused ultrasound (HIFU) can induce thermal and mechanical mechanisms in a well-defined focal volume of tissues. Histotripsy is a form of mechanical HIFU that can initiate and interact with bubble(s) to cause shock scattering and perhaps atomization within the bubble(s) to fractionate most soft tissues. Ultrasonic atomization, or the ejection of fine droplets from an acoustically-excited liquid exposed to air, has been shown to erode planar soft tissue surfaces, which has led to theories that atomization is a mechanism in histotripsy. However, healthy tendons show resistance to conventional histotripsy; pre-treatment of tendons with heat increases susceptibility to histotripsy fractionation. This study investigates ultrasonic atomization and erosion from planar healthy and tendinopathic tendon surfaces as we evaluate HIFU parameters for histotripsy in tendons.Forty-sixbovine tendon-air interfaces were pre-conditioned to surface wetting, heat baths of 20 °C (unaltered), 37 °C (body temperature), and 58 °C (collagen degradation), collagenase soaks for 1, 3, 5, and 24 h (mimicking tendinopathic tendons), and phosphate buffered saline soaks for 24 h. Ejected fragments, histology, and gross analysis determined erosion success. Tissue displacement from the HIFU radiation force was monitored with high-speed photography, and tissue relaxation was pixel-tracked and fit to a Kelvin-Voigt model to evaluate changes in viscoelastic properties.Results showed that atomization produced holes in 24 h collagenase tendons and surface pitting in 58 °C, 3 h, and 5 h collagenase tendons. Increased mound heights and viscoelastic constants in pre-heated (to 58 °C) and collagenase-soaking (3+ hours) tendinopathic models caused a decrease in elasticity and/or increase in viscosity, increasing susceptibility to erosion by HIFU atomization.Therefore, tendons with chronic tendinopathies may be more susceptible than healthy tendons to histotripsy fractionation.
高强度聚焦超声（HIFU）可以在组织的一个定义明确的焦点体积中引起热和机械机制。组织内超声破碎是一种机械 HIFU 形式，它可以引发和与气泡相互作用，导致气泡内的冲击波散射，甚至可能使气泡内的雾化，从而使大多数软组织碎裂。已经证明，超声雾化，即暴露于空气中的受激液体中的细液滴的喷射，会侵蚀平面软组织表面，这导致了雾化是组织内超声破碎的一种机制的理论。然而，健康的肌腱对传统的组织内超声破碎具有抵抗力；肌腱的热预处理会增加对组织内超声破碎分割的敏感性。本研究通过评估肌腱中组织内超声破碎的 HIFU 参数，研究了平面健康和腱病肌腱表面的超声雾化和侵蚀。46 个牛肌腱-空气界面被预处理为表面润湿，20°C（未改变）、37°C（体温）和 58°C（胶原降解）的热浴，胶原酶浸泡 1、3、5 和 24 h（模拟腱病肌腱），以及磷酸盐缓冲盐水浸泡 24 h。喷射碎片、组织学和大体分析确定了侵蚀的成功。用高速摄影监测了来自 HIFU 辐射力的组织位移，并对组织松弛进行了像素跟踪，并拟合到 Kelvin-Voigt 模型中，以评估粘弹性特性的变化。结果表明，24 h 胶原酶肌腱中雾化产生了孔，58°C、3 h 和 5 h 胶原酶肌腱中表面有麻点。预先加热（至 58°C）和胶原酶浸泡（3 小时以上）的腱病模型中凸起高度和粘弹性常数的增加导致弹性降低和/或粘度增加，从而增加了对 HIFU 雾化侵蚀的敏感性。因此，患有慢性腱病的肌腱可能比健康肌腱更容易受到组织内超声破碎的分割。
