磁性人工耳蜗植入手术中耳蜗的三维热模型
A three-dimensional thermal model of the human cochlea for magnetic cochlear implant surgery
摘要：
在传统的人工耳蜗植入手术中，在电极阵列插入期间可能发生物理创伤。已经提出了电极阵列的磁引导以减轻这种医疗并发症。插入后，必须通过加热过程将连接到电极阵列头端的引导磁体分离并移除。然而，这种加热过程可能导致耳蜗内的热创伤。在这项研究中，一个经过验证的三维有限元热传递模型的人耳蜗应用于执行必要的耳蜗内热分析，以确保安全的磁铁移除阶段。具体地，分离磁体的最大安全输入功率密度被确定为边界条件、加热持续时间、耳蜗尺寸、植入电极阵列半径和插入深度、磁体尺寸和耳蜗流体的函数。量纲分析和数值模拟表明，最大安全输入功率密度随耳蜗尺寸和电极阵列半径的增大而增大，随电极阵列插入深度和磁体尺寸的增大而减小。从热的角度来看，最好的耳蜗液是外淋巴液和肥皂液。即使在最差情况下（假设耳蜗壁除圆窗外均为绝热），最大安全输入功率密度也大于熔化1 $\rm{mm^3}$石蜡（将磁体粘合到植入电极阵列）所需的功率密度。通过将这项工作的结果与磁性插入过程的设计的其他方面相结合，即磁性引导过程和医疗要求，将有可能实施热安全的患者特定外科手术。
英文摘要：
In traditional cochlear implant surgery, physical trauma may occur during electrode array insertion. Magnetic guidance of the electrode array has been proposed to mitigate this medical complication. After insertion, the guiding magnet attached to the tip of the electrode array must be detached via a heating process and removed. This heating process may, however, cause thermal trauma within the cochlea. In this study, a validated three-dimensional finite element heat transfer model of the human cochlea is applied to perform an intracochlear thermal analysis necessary to ensure the safety of the magnet removal phase. Specifically, the maximum safe input power density to detach the magnet is determined as a function of the boundary conditions, heating duration, cochlea size, implant electrode array radius and insertion depth, magnet size, and cochlear fluid. A dimensional analysis and numerical simulations reveal that the maximum safe input power density increases with increasing cochlea size and the radius of the electrode array, whereas it decreases with increasing electrode array insertion depth and magnet size. The best cochlear fluids from the thermal perspective are perilymph and a soap solution. Even for the worst case scenario in which the cochlear walls are assumed to be adiabatic except at the round window, the maximum safe input power density is larger than that required to melt 1 $\rm{mm^3}$ of paraffin bonding the magnet to the implant electrode array. By combining the outcome of this work with other aspects of the design of the magnetic insertion process, namely the magnetic guidance procedure and medical requirements, it will be possible to implement a thermally safe patient-specific surgical procedure.
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