Computed SAR and thermal elevation in a 0.25-mm 2-D model of the human eye and head in response to an implanted retinal stimulator - Part I: Models and methods
Computed SAR and thermal elevation in a 0.25-mm 2-D model of the human eye and head in response to an implanted retinal stimulator - Part I: Models and methods
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DOI：
10.1109/tap.2003.816395
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发表时间：
2003-09-01
影响因子：
5.7
通讯作者：
Humayun, MS
中科院分区：
文献类型：
--
作者：
DeMarco, SC;Lazzi, G;Humayun, MS
视网膜色素变性和年龄相关性黄斑变性通过视网膜光感受器的进行性丧失而导致失明。目前正在尝试构建一种视觉假体，以便在植入式电子设备的帮助下为这些患者恢复有限的视觉。这些微芯片的功能是提供电刺激现有的可行的视网膜组织-活神经节和双极细胞-使用芯片上的刺激电路的阵列，而占主导地位的机制，电力和数据。用于这些植入装置的通信是使用线圈的无线感应遥测。本文描述了用于估计在人眼和周围头部组织中引起的加热的方法和模型，该视网膜假体的操作。利用一种新的半自动图形分割算法，建立了一个二维0.25 mm高分辨率人头模型。用于电磁和热建模的基于有限差分的数值方法已用于确定特定吸收率（与植入物的2 MHz感应耦合相关）和刺激器集成电路（IC）功率对不同操作条件下组织加热的影响以及对复杂植入电路的脉络膜血流和特性的不同假设。本文第11部分提供的结果表明，对于60电极视网膜假体芯片，在脉络膜血流不存在和存在的情况下，人眼玻璃体中部的温度分别升高约0.6和0.4 ℃。相应的温度上升约0.19和0.004 degreesC的视网膜上获得这些情况下。在犬眼内加热与体内实验测量的比较显示出良好的一致性。
Retinitis pigmentosa and age-related macular degeneration lead to blindness through progressive loss of retinal photoreceptors. Attempts are under way to construct a visual prosthesis to recover a limited sense of vision for these patients with the aid of implantable electronic devices. The function of these microchips is to provide electrical stimulation to existing viable retinal tissues-living ganglion and bipolar cells-using an array of on-chip stimulus circuits, while the dominant mechanism for power and data. communication for these implanted devices has been wireless inductive telemetry using coils. This paper describes methods and models used to estimate the heating induced in the human eye and surrounding head tissues subject to the operation of this retinal prosthesis. A two-dimensional 0.25-mm high-resolution human head model has been developed with the aid of a new semiautomatic graphical segmentation algorithm. Finite-difference-based numerical methods for both electromagnetic and thermal modeling have been used to determine the influence of the specific absorption rate (associated with 2-MHz inductive coupling to the implant) and of stimulator integrated circuit (IC) power on tissue heating under different operational conditions and different hypothesis on choroidal blood flow and properties of the complex implanted circuitry. Results, provided in Part 11 of this paper, show that temperature increases of approximately 0.6 and 0.4degreesC are induced in the midvitreous of the human eye in the absence and presence of choroidal blood flow, respectively, for a 60-electrode retinal prosthesis chip. Correspondent temperature rises of approximately 0.19 and 0.004degreesC on the retina are obtained for these cases. Comparison with in vivo experimental measurements on intraocular heating in dog eyes shows good agreement.