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。     

重复经颅磁刺激仪的优化设计

本文建立了RLC磁刺激仪模型 ,给出了模型参数计算方法。将磁刺激系统的性能指标分为三部分 :反映磁刺激仪输出性能的损耗能量 ;反映线圈输出性能的峰值磁能 ;反映线圈结构的几何变量。在给定磁刺激条件下 ,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磁刺激仪和线圈输出性能值 ,从而 ,寻找最优的系统参数。优化结果表明 :线圈外半径和线的直径 (或截面面积 )是关键因素 ,选择合适的线圈外半径和线结构可以大大降低功耗 ,提高磁刺激频率 ,解决线圈发热问题     

磁刺激人体可兴奋组织的建模及其感应电场的三维分析

磁刺激是利用时变电流流入线圈,产生时变磁场,从而在组织内感应出电流使某些可兴奋性组织产生兴奋的一种无创的诊断和治疗技术.本文建立了磁刺激可兴奋性组织的一般模型.确定了一些无量纲参数,对感应电场的分布函数进行无量纲化,并给出了电场强度三维分布的计算机仿真.文中分析和讨论了决定刺激聚焦和刺激深度的因素,确定了设计合理的磁刺激线圈和可以使刺激效果和磁刺激装置都得到优化的依据.     

经颅磁刺激技术在癫癎研究中的应用

1经颅磁刺激的原理和方法 根据法拉第电磁原理,电流流过线圈会使线圈产生磁场,该磁场会对在附近的另一个线圈内诱发出电流活动.     

磁刺激八字线圈变形对空间磁场与感应电场分布的影响

在经颅磁刺激中,尽管传统八字线圈的聚焦性要优于圆形线圈的聚焦性,但是八字线圈的两侧边缘产生的磁场与感应电场的峰值仍然较高。设计一种基于折叠变形的八字线圈,通过数值计算分析变形八字线圈空间磁场与感应电场的分布,并与传统八字线圈进行对比。结果表明,当变形八字线圈的折叠角度在45°～60°范围内时,其中心位置产生的空间磁场和感应电场占传统八字线圈在中心位置的90%左右,而变形线圈两侧产生的空间磁场与感应电场占传统八字线圈两侧的30%左右。因此,在空间磁场和感应电场的聚焦度方面,折叠变形八字线圈均优于传统八字线圈。所提出的折叠变形八字线圈为设计新型经颅磁刺激线圈提供了新的思路。     

经颅磁刺激仪线圈位姿调整装置

为了解决传统经颅磁刺激仪刺激线圈位姿固定,导致输出磁场刺激部位调节困难的问题,本研究设计并仿真了一种经颅磁刺激仪线圈位姿调整装置,设计了线圈位姿调整装置的机械结构,建立系统坐标系、线圈和人脑有限元模型,分析在刺激电参数相同、机械结构参数不同条件下,线圈刺激颅脑的磁场分布.随着刺激线圈位姿的调整,磁场刺激颅脑的部位发生改...     

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.     

磁刺激人体可兴奋组织的模及其感应电场的三维分析

磁刺激是利用时变电流流入线圈,产生时变磁场,从而在组织内感应出电流使某些可兴奋性组织产生兴奋的一种无创的诊断和治疗技术。本文建立了磁刺激可兴奋性组织的一般模型。确定了一些无量纲参数,对感应电场的分布函数进行无量纲化,并给出强度三维分布的计算机仿真。文中分析和讨论了决定刺激聚焦和刺激深度的因素,确定了设计合理的磁刺激线圈和可以使刺激效果和磁刺激装置都得到优化的依据。     

连续经颅磁刺激睡眠仪系统的设计

目的为了寻求合适的经颅磁刺激模式治疗失眠等神经系统类的疾病,设计出一种新型的连续经颅磁刺激系统。方法采用PC和单片机交互控制,改进后级TDA7294功放电路,实现0.001Hz～20.000kHz的连续大功率输出驱动线圈产生交变磁场。结果实现了将真实睡眠脑电信号、音乐信号及几种典型波形的刺激信号转换成空间交变磁场直接耦合进大脑的睡眠中枢,同时对圆形线圈在真实头模型下的磁场和感应电流分布进行了有限元仿真。结论系统达到了预定指标,为进一步临床研究提供了可靠的实验平台。     

磁刺激中深度感应电场分布的计算

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组织的过程.根据磁刺激感应电场理论,计算8字形和四叶形线圈刺激深度感应电场的分布.结果表明通过线圈的电流方向直接影响感应电场的聚焦性.8字形线圈电流方向相反时用于刺激大脑皮层神经效果较好,而四叶形线圈电流方向左右相反,上下相同时,刺激外周神经纤维效果较好.     

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。     

微机式磁刺激系统的设计仿真与建模研究

磁刺激技术作为医学康复一种非侵入式的诊疗技术,是当前该领域国际范围的一项重要的研究课题.目前,所用的磁刺激仪存在两大问题:①磁线圈聚焦性较差;②系统能耗较大.刺激阈值所需要的能耗大,由此仪器产热并造成刺激有效性降低.本文在近几年磁刺激技术研究的基础上,运用计算机对磁刺激系统的重要模块进行了仿真,其中包括主电路与微机控制电路的仿真,并对磁刺激线圈磁场进行建模研究,为日后的研究和实践提供了有益的理论依据.     

磁刺激8字形线圈的结构对感应电场分布影响

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组织的过程.8字形线圈由于结构简单,常用于磁刺激中.故根据磁刺激感应电场理论,对8字形线圈改进了两种空间结构,计算其刺激深度感应电场分布,并与改进前作比较,结果表明扇形空间结构聚焦性好,更利于磁刺激兴奋点定位.     

经颅磁刺激电场分析研究进展

经颅磁刺激是一种利用通电线圈在脑部的诱发电场来调节皮质兴奋性的技术,广泛应用于神经病学、康复学等领域。经颅磁刺激诱发电场分析与安全性、刺激效果密切相关,在优化刺激方案、线圈设计方面具有重要意义,成为相关领域的研究重点。首先介绍经颅磁刺激3种常见的临床副作用,然后阐述经颅磁刺激现有研究中的常规电场分析方法,包括解析法和数值分析法及其应用场景,并讨论与电场分析密切相关的生物模型建模方法。此外,由于磁刺激线圈与组织中电场分布的密切相关性,介绍常规的刺激线圈结构类型,并结合磁刺激线圈的7种典型设计,分析基于有限元分析的球模型下的电场分布特征。最后,展望经颅磁刺激电场分析研究未来的发展趋势。     

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.     

Facilitatory effect on the motor cortex by electrical stimulation over the cerebellum in humans

Electrical stimulation over the cerebellum is known to transiently suppress the contralateral motor cortex in humans. However, projections from the cerebellar nuclei to the primary motor cortex are disynaptic excitatory pathways through the ventral thalamus. In the present investigation we studied facilitatory effects on the motor cortical excitability elicited by electrical stimulation over the cerebellum by recording surface electromyographic (EMG) responses from the first dorsal interosseous (FDI) muscle in nine normal volunteers. For primary motor cortical activation magnetic stimuli were given over the contralateral hand motor area with a figure-of-eight shaped coil with a current to preferentially elicit I3-waves (test stimulus). For cerebellar stimulation high-voltage electric stimuli were given with an anode on the ipsilateral mastoid process and a cathode over the contralateral process as previously described (conditioning stimulus). The effect of conditioning-test interstimulus intervals was investigated. Anodal cerebellar stimuli increased the size of EMG responses to magnetic cortical stimulation at an interstimulus interval of 3 ms. Reversing the current of conditioning stimulus abolished the facilitation. The same (anodal) conditioning stimuli did not affect electrically evoked cortical responses. Based on the effective polarity of the conditioning stimulus and the time course of facilitation we consider that this effect is due to motor cortical facilitation elicited by activation of the excitatory dentatothalamocortical pathway at the deep cerebellar nuclei or superior cerebellar peduncle. We conclude that the motor cortical facilitation is evoked by cerebellar stimulation in humans     

Technical approaches to hemisphere-selective transcranial magnetic brain stimulation

Clinical application of transcranial magnetic brain stimulation is mainly used to determine central motor conduction times. With the stimulation coil (Magstim 200, Novametrix) centered conventionally over the midline of the skull convexity and using high stimulus intensities, which are often required in pathological states, the motor cortices of both hemispheres are usually activated simultaneously. Under this condition it is not possible to determine from which hemisphere the descending excitatory volleys to a particular motoneurone pool originate and how the input to the lower motoneurons is organized (uni-/bilateral, ipsi-/contralateral). This limitation can be overcome by two different techniques for selective stimulation of the motor cortex of one hemisphere without coactivation of the other even when using maximal stimulus intensities: 1. A large 12 cm (outer diameter) stimulation coil could be used for selective stimulation when a) the magnetic field radiated over the non-stimulated hemisphere is modified by using a prototype coil shield covering the half of the coil over the nonstimulated hemisphere in combination with b) placing the coil away from the midline towards the preferentially excited hemisphere. The coil shield consists of a sheet of a nickel iron alloy which alters the time course of the induced currents by reducing the initial rate of current intensity change (dI/dt). 2. The use of a smaller 6.5 cm (outer diameter) coil also provided a useful tool for selective stimulation of one hemisphere but was restricted to subjects with low excitation thresholds. In subjects with high excitation thresholds the described use of the large stimulation coil is advisable.     

Effect of tonic voluntary activity on the excitability of human motor cortex.

1. The threshold for obtaining EMG responses after transcranial magnetic stimulation of the brain is reduced by voluntary contraction of the target muscle. The present experiments tested whether some of this effect is due to increased cortical, as opposed to spinal, excitability during the contraction. 2. Magnetic stimulation was delivered with a figure-of-eight coil oriented with the junction region along the interaural line and also (in 4 of 7 subjects) with a circular coil centred at the vertex. The intensity of the conditioning stimulus was subthreshold for evoking a motor response in the relaxed wrist flexor muscles of the forearm. The presence of a small descending corticospinal volley in both the relaxed and active conditions was detected by measuring the facilitation of test H reflexes elicited in the flexor muscles of the forearm. 3. In all subjects, magnetic stimulation with either coil facilitated the H reflex at conditioning-test intervals of -1 to -3 ms (median nerve stimulus before magnetic). This was followed by a long-lasting facilitation. In three of the seven subjects stimulation with the figure-of-eight coil elicited an additional, earlier peak of facilitation at a conditioning-test interval of -3 to -5 ms. 4. In all subjects, the threshold for obtaining facilitation of the H reflex using a conditioning-test interval of -1 to -3 ms was reduced, and the amount of facilitation was larger, if subjects performed a weak tonic voluntary contraction. In contrast, with a conditioning-test interval of -3 to -5 ms voluntary contraction had no effect on the threshold. 5. It is suggested that H reflex facilitation at the conditioning-test interval of -1 to -3 ms was produced by indirect activation of corticospinal neurones by the magnetic stimulus, whereas at -3 to -5 ms, the facilitation was produced by direct activation of corticospinal axons. It is concluded that tonic voluntary contraction of a target muscle decreases the threshold for indirect activation of corticospinal neurones but not for direct stimulation of their axons.