深部经颅磁刺激模拟与实现

Transactional magnetic stimulation (TMS) uses rapidly changing magnetic fields to induce electric fields in the brain. As a noninvasive method to stimulate brain, TMS has attracted considerable interests as an important tool for studying the functional organization of the human brain as well as a therapeutic tool to improve psychiatric disease. .Stimulation of deep brain regions noninvasively may have an important role as a therapy to treatment of several neurological diseases. However, standard TMS devices using round or figure-of-eight coils are not capable of stimulating deep brain regions directly. Because the fields induced by these coils decrease rapidly as a function of depth. Therefore the focus of the present proposal is on the development of deep transcranial magnetic stimulation (dTMS) by realization of the following goals: 1. high enough electric field intensity in the desired deep brain region that will surpass the threshold for neuronal activation, 2.small enough electric field intensity in superficial cortical regions of the brain. For realization of the goals, it is necessary to implement the following investigations:.To develop 3D person-specific head models from high resolution magnetic resonance (MR) images. Important brain sub-regions such as medulla-oblongata, midbrain, pineal-body, pons and thalamus etc. will be distinguished during the segmentation. .To perform numeric simulations of the electrical field induced by several types of coils and accordingly an optimized coil for deep brain stimulation will be designed..To develop 3D person-specific head models by considering white matter anisotropy. The anisotropy conductivity tensor will be calculated from diffusion tensor MRI (DT-MRI) and will be incorporate in our Impedance Method codes. Dependence of induced electric fields on white matter anisotropy will be investigated..To design and realize a novel TMS device that use a circuit topology incorporating insulated-gate bipolar transistor (IGBT) to generate pulses with adjustable pulse width. The new device is promising in the application of dTMS as it is expected to reduce energy dissipation and coil heating greatly compared to conventional monophasic and biphasic TMS..The electrical field induced by the new coil design will be measured in a phantom brain and compared with the numerical simulation results. .It is hoped that this study will be helpful in introducing dTMS as a promising tool for treatment of depression and Parkinson disease.

经颅磁刺激是利用快速变化的磁场在脑部产生感应电场。标准经颅磁刺激线圈产生的交变磁场随距离的增大而迅速衰减，无法刺激脑深部组织。因此，本课题将重点研究深部经颅磁刺激(dTMS)，并实现以下目标：1.在脑深部靶组织中产生出超过神经元兴奋阀值的高聚焦度的感应电场；2. 在浅层皮质等非靶组织中感应电场尽可能小。为达此目的，开展以下研究内容：利用高分辨率核磁共振图象重构三维头模型，并分割出重要的脑区，比如延髓，松果体，脑桥，丘脑等。通过数值模拟与优化设计，确定适于dTMS的线圈结构。计算脑白质电导率张量并嵌入阻抗法计算程序，研究脑白质各向异性对dTMS感应电场分布的影响。研制深部经颅磁刺激实验装置，产生的刺激脉冲参数可调。通过调节脉宽，降低磁刺激器功率损耗与线圈热损耗，并提高刺激深度。本课题的研究成果将为包括抑郁症、帕金森病等神经与精神疾病的治疗提供一种新方法。

背景：经颅磁刺激(TMS)是利用放置于头部的线圈，通过通以脉冲电流，产生快速变化的磁场在脑部产生感应电场，引起皮层组织的神经兴奋。TMS已经成功应用在抑郁症等神经与精神疾病的治疗中。标准经颅磁刺激线圈产生的交变磁场随距离的增大而迅速衰减，无法刺激脑深部组织(距离头顶4-8 cm)，因此，有必要开展深部经颅磁刺激(deep-TMS)的研究，尤其是实现在脑深部靶组织中产生超过神经元兴奋阀值的高聚焦度感应电场的同时，在浅层皮质等非靶组织中感应电场尽可能小。.研究内容：利用高分辨率核磁共振图象重构三维头模型，并分割出重要的脑区，比如延髓，松果体，脑桥，丘脑等。通过数值模拟与优化设计，确定了适于dTMS 的线圈结构。计算了脑白质电导率张量并研究脑白质各向异性对dTMS 感应电场分布的影响。研制深部经颅磁刺激实验装置，产生的刺激脉冲参数可调。.重要结果：1. 完成构造了包含40多种不同脑组织及重要的脑区的三维真实头模型。2. 设计了具有复杂结构的经颅磁刺激线圈，它们是：锥形线圈 (Double-cone coil)，H-线圈，Halo-线圈，同轴圆线圈组，Halo-8字线圈组。计算了这些线圈作用下空间磁感应强度的分布，以及真实人脑中感应电流、感应电场的分布，并将计算结果与常规的“8字”线圈在刺激深度与聚焦度方面的优劣进行了系统的比较。3. 研制了经颅磁刺激装置，系统研究了磁刺激系统放电线圈及回路参数对线圈放电电流特性的影响。 4. 利用低成本、小容量IGBT的模块的并联，实现了10kA的放电电流，线圈表面的磁感应强度的峰值可以达到5个特斯拉。.关键数据: 发表论文31篇， 其中被SCI收录2篇， 被EI收录19篇， 被北大中文核心期刊库收录16篇。合著英文专著一部(完成其中的一章)。.科学意义：本课题的研究成果将为包括顽固性抑郁症、帕金森病等与深部脑组织病变相关神经与精神疾病的治疗提供一种新方法。