Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America.
Boston VA Medical Center, Boston, MA, United States of America.
J Neural Eng. 2023 Jul 26;20(4). doi: 10.1088/1741-2552/ace79a.
Micro magnetic stimulation of the brain via implantable micro-coils is a promising novel technology for neuromodulation. Careful consideration of the thermodynamic profile of such devices is necessary for effective and safe designs.We seek to quantify the thermal profile of bent wire micro-coils in order to understand and mitigate thermal impacts of micro-coil stimulation.. In this study, we use fine wire thermocouples and COMSOL finite element modeling to examine the profile of the thermal gradients generated near bent wire micro-coils submerged in a water bath during stimulation. We tested a range of stimulation parameters previously reported in the literature such as voltage amplitude, stimulus frequency, stimulus repetition rate and coil wire materials.. We found temperature increases ranging from <1 °C to 8.4 °C depending upon the stimulation parameters tested and coil wire materials used. Numerical modeling of the thermodynamics identified hot spots of the highest temperatures along the micro-coil contributing to the thermal gradients and demonstrated that these thermal gradients can be mitigated by the choice of wire conductor material and construction geometry.. ISO standard 14708-1 designates a thermal safety limit of 2 °C temperature increase for active implantable medical devices. By switching the coil wire material from platinum/iridium to gold, our study achieved a 5-6-fold decrease in the thermal impact of coil stimulation. The thermal gradients generated from the gold wire coil were measured below the 2 °C safety limit for all stimulation parameters tested.
通过植入式微线圈对大脑进行微磁刺激是一种有前途的新型神经调节技术。为了进行有效的安全设计，有必要仔细考虑此类设备的热力学特性。我们旨在量化弯曲丝微线圈的热特性，以了解和减轻微线圈刺激产生的热影响。在这项研究中，我们使用细金属丝热电偶和 COMSOL 有限元建模来研究在刺激过程中浸入水浴中的弯曲丝微线圈附近产生的热梯度分布。我们测试了一系列先前在文献中报道的刺激参数，例如电压幅度、刺激频率、刺激重复率和线圈丝材料。我们发现，根据所测试的刺激参数和线圈丝材料的不同，温度升高幅度从<1°C到 8.4°C 不等。热力学的数值建模确定了微线圈上温度最高的热点，这些热点导致了热梯度，并表明通过选择导线材料和结构几何形状可以减轻这些热梯度。ISO 标准 14708-1 为有源植入式医疗器械指定了 2°C 的温升热安全限值。通过将线圈丝材料从铂/铱切换为金，我们的研究将线圈刺激的热影响降低了 5-6 倍。对于所有测试的刺激参数，金丝线圈产生的热梯度均低于 2°C 的安全限值。
