磁刺激用平面线圈结构的优化研究

文中建立了采用任意形状平面线圈磁刺激仪的RLC模型，给出了模型参数的计算方法。为了优化线圈，将磁刺激仪线圈的性能指标分为反映线圈输出性能的峰值磁能和反映线圈结构的几何变量。在磁刺激激活函数达到阈值条件下，调整平面螺旋线圈的结构并计算出依赖于线圈结构参数的输出性能值，从而，寻找最优的线圈几何参数。优化结果表明：线圈外半径是关键因素，给定阈值条件，选择合适的线圈外半径，可以大大降低线圈峰值磁能；另外，现在使用的圆环线圈并非最优，D形线圈优于圆环线圈。     

功能磁刺激技术的研究

功能磁刺激是一种全新的生物组织刺激技术，以其可以兴奋神经肌肉的特点，及可进行深部刺激、无痛、非介入，易于操作等优点，具有广阔的应用前景。本文详细介绍了功能磁刺激技术的原理及磁刺激系统，介绍了目前磁刺激技术中线圈设计和实验研究成果，以及和我们在磁刺激镇痛方面的工作。     

面向鸽子机器人的磁刺激线圈仿真设计及实验研究

为了探究将磁刺激技术应用于动物机器人运动控制的可行性,本文面向鸽子机器人,仿真分析线圈半径、匝数等因素对磁刺激强度、深度及聚焦性的影响,提出线圈设计方案。将线圈置于鸽子头部及腿部,磁刺激同时记录腿部肌电。结果发现,磁刺激时肌电明显增强。降低磁刺激系统输出频率,输出电流增大,肌电随之增强。与脑部磁刺激相比,刺激坐骨神经引起的肌电增强反应更为显著。这表明,磁刺激系统通过驱动该线圈可以有效地实现对脑及外周神经功能的调控。本研究为后续实用性线圈优化改进提供了理论及实验指导,为动物机器人磁刺激运动控制实施奠定了初步的理论和实验基础。     

经颅磁刺激线圈的磁聚焦优化设计

经颅磁刺激是利用变化磁场产生的感应电场作用于可兴奋人体脑组织的过程,磁聚焦性能是经颅磁刺激线圈设计的一项重要指标。根据磁刺激线圈感应电场理论,我们设计了半圆螺线管用于经颅磁刺激,计算了其载流线圈随刺激深度的感应电场分布,并与传统的经颅磁刺激8字形线圈作比较。结果表明,半圆螺旋管线圈既继承了8字形线圈感应电场的主瓣聚焦性强的优良特性,又摒弃了其相对较大的旁瓣对浅表非靶组织的兴奋刺激的不良影响,完全达到了磁聚焦优化设计的目的,也更利于磁刺激兴奋点的定位。     

磁刺激中线圈感应电场的聚焦性研究

根据磁刺激线圈感应电场理论,对圆形线圈、8字形线圈、四圆形线圈和四叶形线圈感应电场的分布进行研究,结果表明四叶形聚焦性好,更利于磁刺激兴奋点的定位.     

一种抑制反向感应电场的磁刺激线圈设计方法探讨

在无创性脑神经磁刺激技术中,多采用8字形磁刺激线圈,在线圈周围一定距离的空间中,对应8字线圈中心出现感应电场最大值,对应两个边缘处出现反向感应电场峰值,后者容易在刺激目标处产生副刺激,分析了8字形磁刺激线圈感应电场的分布,针对其反应方向感应电场幅值较大,容易引起副刺激的问题提出了新的磁刺激线圈设计方法,以抑制感应电场副峰,并进行了计算机模拟和验证。     

经颅磁刺激中刺激线圈的仿真研究

目的设计用于经颅磁刺激的线圈,要求能够对大脑皮质进行多点刺激,且具有聚焦性好、制作简单、使用方便等特点。方法利用电磁仿真方法,以圆形线圈和8字形线圈为基础,计算线圈在均匀人体模型中感应电场的分布情况,比较尺寸、绕法对经颅磁刺激线圈的聚焦性和刺激深度的影响。在此基础上设计了一种多圆相切线圈,并计算该线圈在均匀人体和真实头部模型中的电场分布。结果感应电场强度随刺激深度的增加呈指数式衰减。减小圆形线圈的尺寸,会提高聚焦性,同时可减弱感应电场强度。8字形线圈比圆形线圈具有更好的聚焦性,多层绕法综合效果较好。多圆相切线圈具有8字形线圈的优点,且可以进行多点刺激。结论尺寸、绕法等因素对线圈的聚焦性和刺激深度具有重要影响,多圆相切线圈在经颅磁刺激中具有很好的应用前景。真实头部模型仿真,对于线圈的设计和靶区定位具有重要意义。     

脑神经磁刺激技术的研究

生物组织磁刺激技术是一种无创伤生物刺激技术，在脑神经刺激以及深部神经刺激中较之传统电刺激具有明显优势，近１０几年来发展较迅速，本文概述了磁刺激技术的基本原理，介绍了脑部磁刺激常用的球形头模型和计算颅内感应电场分布的数学模型，分析了线圈设计中不同的结构，形状，大小，方向等对感应电场聚焦性的影响，比较了圆形（包括圆形的变形）线圈，八字形线圈，Ｓｌｉｎｋｙ线圈刺激脑部神经的基本特性，此外还简单描述了刺激     

用于经颅磁刺激铁芯线圈的仿真研究

目的 研究铁芯线圈感应电场的仿真方法,分析铁芯截面大小对线圈性能的影响.方法 针对铁芯线圈结构复杂及存在非线性介质的特点,采用有限元分析软件Ansoft对铁芯线圈模型进行瞬态磁场仿真,求解不同铁芯大小的线圈模型在空间域的感应电流分布,利用静态仿真求解电感值.结果 计算出不同线圈在深度5 mm沿坐标轴的电场分布曲线,并统计曲线中旁峰值与最大值之比.对比仿真结果发现随着铁芯截面增大,线圈的刺激强度与电感值增加,聚焦性能先增强后减弱.当铁芯截面约为空心区域面积1/16时,铁芯线圈聚焦性最好.结论 本研究对带铁芯磁刺激线圈的设计具有参考作用.     

提高脑神经磁刺激感应电场聚焦性能的线圈参数优化方法的研究

本研究提出一个衡量磁刺激线圈聚焦性的比较系数,比较不同形状线圈的感应电场聚焦性,研究线圈参数的优化方法.我们建立了磁刺激感应电场分布的数学模型,以Matlab作为仿真工具,以能够反映线圈刺激效果的比较系数ξ为指标,分析比较了几种不同线圈的聚焦性,以及成不同角度的线圈聚焦性.结果表明:四叶玫瑰形为刺激聚焦性最好的线圈形状,该线圈半径越小,聚焦性越好,成102°角的四叶玫瑰线形线圈具有最佳聚焦性,而且112°角四叶玫瑰形线圈与89°角线圈组合成的线圈阵列聚焦性最好.由此说明本研究中的比较系数可用于比较线圈聚焦性,对线圈参数的优化设计具有一定的指导意义.     

经颅磁刺激放电回路参数对线圈脉冲电流特性的影响

目的 本文分析了经颅磁刺激放电回路参数,包括放电回路中总电容（C）、放电电压（U）以及放电线圈的电感值（L）和电阻值（R）对线圈放电电流特性的影响,为经颅磁刺激放电回路参数的优化提供理论指导.方法 首先理论上对经颅磁刺激系统基本电路进行分析,得出放电电流与放电回路参数的关系式,然后通过仿真和实验相结合的方法,研究放电回路参数对线圈脉冲电流的影响.同时,利用傅里叶变换分析线圈脉冲放电电流的频域特性.结果 单独增大储能电容值,增大了线圈放电电流幅值,延长了脉冲电流上升沿时间和脉宽持续时间,减小了电流信号的主频.单独减小回路总电阻值,增大了脉冲电流的幅值,提高了电流信号的主频,但更容易使脉冲电流出现多次振荡.单独增大回路电感值,减小了脉冲电流幅值,延长了脉冲电流的上升沿时间和脉宽持续时间,电流信号主频先增大后减小.结论 在经颅磁刺激系统工程设计中,放电回路参数值要匹配,不同的回路参数取值直接影响线圈脉冲电流的特性.本研究对设计特定指标要求的经颅磁刺激系统具有理论参考价值.     

Some technical aspects of magnetic stimulation coil design with the ferromagnetic effect

The performance of the stimulation coil in a magnetic nerve stimulator can be improved by attaching a ferromagnetic structure to the coil. This reduces heat generation at the coil and increases magnetic field strength for a given unit of current. Some technical aspects of the design of a stimulation coil with a ferromagnetic structure have been studied. Finite element method analysis results are presented for the effect of size, depth and magnetic saturation of the ferromagnetic structure on the stimulation coil performance. The experimental results show that the stimulation coil performance is improved by up to 40% by the attaching of a ferromagnetic structure on the coil.     

The effect of head and coil modeling for the calculation of induced electric field during transcranial magnetic stimulation

In the present work we studied some of the features related to transcranial magnetic stimulation (TMS) computational modeling. Particularly we investigated the impact of head model resolution on the estimated distribution of the induced electric field, as well as the role of the stimulating magnetic coil model in TMS. Using the impedance method we calculated the induced electric field inside a realistic numerical phantom of the human head from a commercially available eight-shaped coil, which was modeled in two ways. The results showed that finer resolution of the model has better performance at tissue interfaces eliminating numerical artifacts of local peaks. Furthermore, the geometrical details of a TMS coil must be taken into account since the predicted amount of volume of brain tissue involved can have great variation. Finally, the secondary magnetic field that is generated by the induced eddy currents in the tissues can be neglected.     

Transcranial magnetic stimulation in the rat

Transcranial magnetic stimulation (TMS) allows for quantification of motor system excitability. While routinely used in humans, application in other species is rare and little is known about the characteristics of animal TMS. The unique features of TMS, i.e., predominantly interneuronal stimulation at low intensity and non-invasiveness, are particularly useful in evaluating injury and recovery in animal models. This study was conducted to characterize the rodent motor evoked potential to TMS (MEP_TMS) and to develop a methodology for reproducible assessment of motor excitability in the rat. MEP_TMS were compared with responses evoked by electrical stimulation of cervical spinal cord (MEP_CES) and peripheral nerve. MEP were recorded by subcutaneous electrodes implanted bilaterally over the calf. Animals remained under propofol infusion and restrained in a stereotactic frame while TMS followed by CES measurements were obtained before and after 2 h of idle time. TMS was applied using a 5-cm-diameter figure-of-eight coil. MEP_TMS had onset latencies of 6.7±1.3 ms. Latencies decreased with higher stimulation intensity (r=–0.7, P<0.05). Two morphologies, MEP_{TMS, 1} and MEP_{TMS, 2}, were distinguished by latency of the first negative peak (N1), overall shape, and amplitude. MEP_{TMS, 2} were more frequent at higher stimulation intensity. While recruitment curves for MEP_{TMS, 1} followed a sigmoid course, no supramaximal response was reached for MEP_{TMS, 2}. Mid-cervical spinal transection completely abolished any response to TMS. MEP_CES showed a significantly shorter latency (5.29±0.24, P<0.0001). Two types of MEP_CES resembling MEP_{TMS, 1 and 2} were observed. Neither MEP_TMS nor MEP_CES changed on repeat assessment after 2 h. This study demonstrates the feasibility and reproducibility of TMS in the rat. Sigmoid recruitment curves for MEP_{TMS, 1} suggest input-output properties similar to those of the human corticospinal system. Latency differences between CES and TMS point to a supraspinal origin of the MEP_TMS. The two morphologies likely reflect different cortical or subcortical origins of MEP_TMS. Electronic Publication     

Mapping location of excitation during magnetic stimulation: Effects of coil position

We determined the location of excitation for different positions of a round and butterfly coil duringin vitro magnetic stimulation of cut peripheral nerves. We analyzed the conditions under which excitation occurs, either at the termination or at the peak of the field gradients (first spatial derivative of the electric field). These results were then compared to predictions about the location of excitation sites from a theoretical model of magnetic stimulation of finite neuronal structures. Excitation along a straight nerve occurred at terminations when 1) a coil was positioned close to the end of a nerve (at least one diameter length from the end), 2) a nerve ended in a finite terminating impedance much greater than the axial resistance of the nerve, 3) the induced electric field was of sufficient magnitude, pointing in a direction away from the axis of a nerve. Excitation occurred at the negative peak of the field gradients along a nerve when 1) a coil was positioned far away from the ends of a nerve, 2) there were no geometric or volume conductor inhomogeneities around a nerve, and 3) it was of sufficient magnitude. Threshold strengths for excitation at terminations were significantly lower than that for field gradient excitation and comparable to that due to geometric and volume conductor inhomogeneities.     

Evoked motor response thresholds during transcranial magnetic stimulation in patients with symptomatic partial epilepsy

Transcranial magnetic stimulation (TMS) occupies a leading position among noninvasive neurophysiological methods used for evaluating the balance of processes of cortical inhibition and excitation. The aim of the present work was to assess motor cortical excitability in symptomatic partial epilepsy using TMS in relation to the effects of antiepileptic treatment. A total of 31 patients were studied. A decrease in the motor response threshold was seen in a group consisting of untreated patients, with changes in cortical excitability during seizures. Treated patients showed no difference as compared with healthy subjects. The shorter the interval between a seizure and TMS, the smaller the evoked motor response threshold. The low threshold seen in patients with symptomatic partial epilepsy showed a significant correlation with clinical signs of neuromuscular excitability. The data obtained here provide evidence of changes in the functional state of the cortex and, thus, the motor response threshold, in patients with epilepsy. __________ Translated from Zhurnal Nevrologii i Psikhiatrii imeni S. S. Korsakova, Supplement, Epilepsiya, No. 1, pp. 75–78, 2006.     

磁刺激应用及机理研究进展

由于磁刺激技术的有效性和无创性 ,近年来该技术已被应用于临床治疗及脑科学的研究中。本文综述了磁刺激对各种神经性疾病的治疗作用 ,并阐述其主要的作用机理     

Coil optimization for magnetic brain stimulation

Further development of magnetic brain stimulation requires smaller coils, smaller power consumption, and less coil heating. This study addresses the optimization of the complete stimulator and in particular the coil. We describe the coil structure in terms of simple mathematical functions and examine the influence of changes in the structure on several figures of merit. A few optimal coil geometries suitable for repetitive brain stimulation are depicted. It is demonstrated that today’s coils are far from optimal and that, for instance, the power consumption can be reduced remarkably from the level of today's equipment. Improvements may act as a springboard toward new applications.     

Significance of shape and size of the stimulating coil in magnetic stimulation of the human motor cortex

Three different stimulating coil designs were evaluated for magnetic motor cortex stimulation by comparing threshold stimulus intensities at different sites over the scalp for exciting upper and lower limb muscles. Little difference was found between stimulation characteristics of two circular coils of different size, the smaller coil delivering slightly more focal stimuli. A twin coil composed of two single circular coils in series arranged side-by-side, produced significantly more powerful and more focal stimuli. It proved to be superior for exciting the leg muscles, in that less output energy was needed. For all coils, the orientation of the inducing current over the presumed motor area was the most critical stimulation parameter, and a sagittal current in anterior direction or coronal towards the stimulated hemisphere was optimal for the upper limb or lower limb muscles, respectively.