Electromagnetic power absorption and temperature changes due to brain machine interface operation
Electromagnetic power absorption and temperature changes due to brain machine interface operation
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DOI：
10.1007/s10439-007-9264-3
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发表时间：
2007-05-01
影响因子：
3.8
通讯作者：
Rennaker, Robert L.
中科院分区：
文献类型：
--
作者：
Ibrahim, Tamer S.;Abraham, Doney;Rennaker, Robert L.
为了充分了解神经功能，慢性神经记录必须同时从10s或100s的神经元进行。为了实现这一目标，几个小组正在开发脑机接口。为了让这些设备能够长期供人类使用，它们很可能需要通过射频(RF)源从外部进行操作和供电。然而，射频暴露可能会导致组织发热，并受到FDA/FCC的监管。本文提供了与脑机接口(BMI)操作相关的组织加热量和比吸收率(SAR)的初步估计。使用电磁学和生物热现象的模拟，在由18个组织组成的详细解剖的人头网状结构中评估了脑机接口的操作。这些模拟是用一个芯片和八个芯片进行的，这些芯片放置在人脑表面，每个芯片以四个频率(13.6 MHz、1.0 GHz、2.4 GHz和5.8 GHz)供电。模拟芯片由硅片上的线状天线组成，上面覆盖着特氟龙硬脑膜贴片。用时域有限差分法计算SAR值，并用二维生物热方程预测头部电磁吸收引起的峰值温度变化。仅由于合成孔径雷达，就显示出在更高频率下的加热增加，单芯片配置的峰值温度变化约为0.018℃，8芯片配置的峰值温度变化约为0.06℃，每个芯片的功率吸收(人头)为10 mW。此外，还研究了芯片中的功耗引起的温度升高(S)。结果表明，对于神经组织，单芯片结构的最大温升为3.34℃，8芯片结构的最大温升为7.72℃。最后，模拟了在头部温度升高1.0摄氏度(FDA指南中指出的最严格标准)之前每个芯片中允许的最大功耗，发现单芯片配置中的最大功耗为2.92 mW，八芯片配置中为1.25 mW。由于合成孔径雷达引起的热加热微乎其微，这项研究表明，无线电磁学，即射频，可能是临床应用中为脑机接口供电和通信的可行选择。
To fully understand neural function, chronic neural recordings must be made simultaneously from 10s or 100s of neurons. To accomplish this goal, several groups are developing brain machine interfaces. For these devices to be viable for chronic human use, it is likely that they will need to be operated and powered externally via a radiofrequency (RF) source. However, RF exposure can result in tissue heating and is regulated by the FDA/FCC. This paper provides an initial estimate of the amount of tissue heating and specific absorption rate (SAR) associated with the operation of a brain-machine interface (BMI). The operation of a brain machine interface was evaluated in an 18-tissue anatomically detailed human head mesh using simulations of electromagnetics and bio-heat phenomena. The simulations were conducted with a single chip, as well as with eight chips, placed on the surface of the human brain and each powered at four frequencies (13.6 MHz, 1.0 GHz, 2.4 GHz, and 5.8 GHz). The simulated chips consist of a wire antenna on a silicon chip covered by a Teflon dura patch. SAR values were calculated using the finite-difference time-domain method and used to predict peak temperature changes caused by electromagnetic absorption in the head using two-dimensional bio-heat equation. Results due to SAR alone show increased heating at higher frequencies, with a peak temperature change at 5.8 GHz of approximately 0.018 degrees C in the single-chip configuration and 0.06 degrees C in the eight-chip configuration with 10 mW of power absorption (in the human head) per chip. In addition, temperature elevations due to power dissipation in the chip(s) were studied. Results show that for the neural tissue, maximum temperature rises of 3.34 degrees C in the single-chip configuration and 7.72 degrees C in the eight-chip configuration were observed for 10 mW dissipation in each chip. Finally, the maximum power dissipation allowable in each chip before a 1.0 degrees C temperature increase (most stringent standards as denoted in the FDA guidelines) is exceeded in the head was simulated and found to be 2.92 mW in the single-chip configuration and 1.25 mW in the eight-chip configuration. As thermal heating due to SAR was insignificant, this study suggests that wireless electromagnetics, i.e., RF may be a viable option for powering, and communicating with brain machine interfaces for clinical applications.