Recently, our group developed a synergistic brain drug delivery method to achieve simultaneous transcranial hyperthermia and localized blood–brain barrier opening via MR-guided focused ultrasound (MRgFUS). In a rodent model, we demonstrated that the ultrasound power required for transcranial MRgFUS hyperthermia was significantly reduced by injecting microbubbles (MBs). However, the specific mechanisms underlying the power reduction caused by MBs remain unclear. The present study aims to elucidate the mechanisms of MB-enhanced transcranial MRgFUS hyperthermia through numerical studies using the finite element method. The microbubble acoustic emission (MAE) and the viscous dissipation (VD) were hypothesized to be the specific mechanisms. Acoustic wave propagation was used to model the FUS propagation in the brain tissue, and a bubble dynamics equation for describing the dynamics of MBs with small shell thickness was used to model the MB oscillation under FUS exposures. A modified bioheat transfer equation was used to model the temperature in the rodent brain with different heat sources. A theoretical model was used to estimate the bubble shell’s surface tension, elasticity, and viscosity losses. The simulation reveals that MAE and VD caused a and additional temperature rise, respectively. Compared with FUS only, MBs caused a temperature increase, which is consistent with our previous animal experiments. Our investigation showed that MAE and VD are the main mechanisms of MB-enhanced transcranial MRgFUS hyperthermia.

中文翻译：

---

微泡增强经颅磁共振引导聚焦超声脑热疗：利用有限元法研究加热机制


最近，我们课题组开发了一种协同脑部药物输送方法，通过磁共振引导聚焦超声（MRgFUS）实现同时经颅热疗和局部血脑屏障打开。在啮齿动物模型中，我们证明通过注射微泡 (MB) 可以显着降低经颅 MRgFUS 热疗所需的超声功率。然而，MB 导致功耗降低的具体机制仍不清楚。本研究旨在通过有限元方法的数值研究阐明 MB 增强经颅 MRgFUS 热疗的机制。假设微泡声发射（MAE）和粘性耗散（VD）是具体机制。使用声波传播来模拟脑组织中的 FUS 传播，并使用描述小壳厚度 MB 动力学的气泡动力学方程来模拟 FUS 暴露下的 MB 振荡。使用修改后的生物传热方程来模拟具有不同热源的啮齿动物大脑中的温度。使用理论模型来估计气泡壳的表面张力、弹性和粘度损失。仿真表明，MAE 和 VD 分别导致了额外的温升。与单独的FUS相比，MBs引起了温度升高，这与我们之前的动物实验一致。我们的研究表明，MAE 和 VD 是 MB 增强经颅 MRgFUS 热疗的主要机制。