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首页> 外文期刊>Physics in medicine and biology. >The role of acoustic nonlinearity in tissue heating behind a rib cage using a high-intensity focused ultrasound phased array
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The role of acoustic nonlinearity in tissue heating behind a rib cage using a high-intensity focused ultrasound phased array

机译：使用高强度聚焦超声相控阵的声学非线性在肋骨后方组织加热中的作用

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The goal of this study was to investigate theoretically the effects of nonlinear propagation in a high-intensity focused ultrasound (HIFU) field produced by a therapeutic phased array and the resultant heating of tissue behind a rib cage. Three configurations of focusing were simulated: in water, in water with ribs in the beam path and in water with ribs backed by a layer of soft tissue. The Westervelt equation was used to model the nonlinear HIFU field, and a 1 MHz phased array consisting of 254 circular elements was used as a boundary condition to the model. The temperature rise in tissue was modelled using the bioheat equation, and thermally necrosed volumes were calculated using the thermal dose formulation. The shapes of lesions predicted by the modelling were compared with those previously obtained in in vitro experiments at low-power sonications. Intensity levels at the face of the array elements that corresponded to the formation of high-amplitude shock fronts in the focal region were determined as 10 W cm-2 in the free field in water and 40 W cm-2 in the presence of ribs. It was shown that exposures with shocks provided a substantial increase in tissue heating, and its better spatial localization in the main focal region only. The relative effects of overheating ribs and splitting of the focus due to the periodic structure of the ribs were therefore reduced. These results suggest that utilizing nonlinear propagation and shock formation effects can be beneficial for inducing confined HIFU lesions when irradiating through obstructions such as ribs. Design of compact therapeutic arrays to provide maximum power outputs with lower intensity levels at the elements is necessary to achieve shock wave regimes for clinically relevant sonication depths in tissue.
机译：这项研究的目的是从理论上研究由治疗性相控阵产生的高强度聚焦超声（HIFU）场中非线性传播的影响，以及由此引起的肋骨后腔组织加热。模拟了三种聚焦方式：在水中，在光路中带有肋骨的水中和在带有一层软组织支持的肋骨的水中。使用Westervelt方程对非线性HIFU场进行建模，并使用由254个圆形元素组成的1 MHz相控阵作为该模型的边界条件。使用生物热方程对组织中的温度升高进行建模，并使用热剂量公式计算热坏死体积。将通过建模预测的病变形状与先前在低功率超声下的体外实验中获得的形状进行比较。对应于焦点区域中高振幅激波锋面形成的阵列元件表面的强度水平在水中的自由场中确定为10 W cm-2，在存在肋条的情况下确定为40 W cm-2。结果表明，受到电击的情况使组织发热显着增加，并且仅在主焦点区域有更好的空间定位。因此减小了由于肋的周期性结构而引起的肋过热和焦点分裂的相对影响。这些结果表明，当通过肋骨等障碍物照射时，利用非线性传播和激波形成效应可能有助于诱发局限性HIFU病变。设计紧凑的治疗阵列以在元件上提供较低强度水平的最大功率输出，对于实现组织中临床相关超声深度的冲击波方案是必要的。

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