【作者】 金安；

【导师】 张日辉；

【作者基本信息】 吉林大学 ， 生理学， 2010， 博士

【摘要】 磁刺激是一种无痛、无创、安全、易操作的新技术。其基本原理是通过在磁刺激线圈中流过瞬间电流产生一个瞬间磁场,当该磁场作用于人体组织时在体内产生一个感应电场从而引起感应电流。当电流流过大脑皮质时可以改变神经元的兴奋性。临床上应用磁刺激技术治疗多种疾病并且取得了一定的效果。目前磁刺激技术也被人们用于外周组织,心脏作为可兴奋器官,其在磁刺激时的磁场分布方面的研究较少。本文为研究磁刺激对心脏的作用,主要做了以下工作。1.磁刺激系统的分析与设计研制了磁刺激硬件系统,整个系统分为主电路、单片机部分和上位机部分。通过分析磁刺激仪原理设计了主电路,利用MSP430单片机实现了对主电路的控制,使用VB语言编写了上位机通讯软件。该系统可以成功进行单脉冲磁刺激,可以满足单脉冲磁刺激实验研究的基本需要。2.基于CT的心脏三维实体重建利用工具软件把CT图片转化为BMP格式的图片,参照图谱找到心脏边界,交互式医学影像软件得到心脏的点云数据,数据导入三维塑性软件中生成心脏的3D实体模型。3.心脏模型的电磁场有限元分析把心脏模型导入电磁场有限元分析软件,建立线圈和空气模型,设定不同模型的材料属性,设定线圈的参数,施加激励与边界条件,求解得到心脏在磁刺激时表面的磁场分布。更多还原

【Abstract】 Bioelectromagnetics is an intrecross science, its attention is concentrated on the relation and interacting between organisms and electromagnetic field. The ultimate object of this science is the application of the principles of electromagnetic to biology and medicine. Many Studies show that a electromagnetic field of different requency and intensity had different roles in organisms. Magnetic stimulation can be considered a successful applications of the principles of Bioelectromagnetics. The basic principles of magnetic stimulation is producing a vertical temporary magnetic field by flowing the current in the magnetic stimulation coil. The vertical temporary magnetic has great penetration, it can produce a induced electric field on underlying tissues.When a current producing by the induced electric field fiowed on the target tissue, the excitability of the target tissue would be changed. The principle of magnetic stimulation and electrical stimulation is similarity, but the magnetic stimulation have many advantages compared to the electrical stimulation. such as non-pain, non-invasive, great penetration, and simple operation.Many people pay attention to the application value and development prospects of the magnetic stimulation, there are many studys about the clinical application of magnetic stimulation. Present, people have generally regarded that the magnetic stimulation can be use to treat mental illness such as Schizophrenia, depression, obsessive-compulsive disorder, mania, etc, the magnetic stimulation can also be use to treat movement disorders such as Parkinson’s, epilepsy, movement disorders etc, Some people used the magnetic stimulation in rehabilitation,such as Spinal cord injury rehabilitation, prevention of postoperative venous thrombosis patients, the respiratory intensive care and adjustment of patients. Many application of the magnetic stimulation are transcranial magnetic stimulation(TMS). TMS regulated human functioning by changing the brain activity. The study of the safety for the magnetic stimulation show that sTMS and pTMS are safe but rTMS may evoke epilepsy.In the premier study,magnetic stimulation was used as transcranial magnetic stimulation, the later study show that magnetic stimulation could also affect the peripheral nerve and muscle. When heart is stimulated ,the cardiac excitability will be changed. There are many electrical stimulus studys show that ECG, blood pressure, cardiac stroke volume will be changed when heart was stimulated.This change may be owing to myocardial contractility, cardiac excitability or calcium channel permeability. Some experiments show that magnetic stimulation can also affect muscle contraction, ion channel status, peripheral nerve excitability. Therefore, magnetic stimulation and the electrical stimulation will produce similar results at least in the theory. In this paper, mainly works as follows:1. The analysis and design of a sTMSAt first,we analysed the principles of a magnetic stimulation. A magnetic stimulation is a typical RLC discharge circuit, The circuit is a second-order circuit,which can be represent by a linear equations of the second order. According to the different eigenvalue solution, the RLC discharge circuit can be assort to 4 cases: underdamped, overdamped, critical damping and no damping. Magnetic stimulation should be working as a underdamped circuit. we selected discharge circuit component parameters as a underdamped circuit. The control circuit is based on MSP430, Through two series resistors on both ends of the capacitor, the voltage of the capacitor can be measurement through the A / D converter chip, When the measured value reaches the set value, the control circuit will stop charging and begin discharging.The communication between the MCU and the Computer need a power levels changing chip SP3220E,we finishde the communication by writing software.The single-pulse magnetic stimulator which is designed meet the basic requirements of a single pulse magnetic stimulation experiments, The stimulus parameters can be set in the computer user interface, and some interfaces are earmarked for the ECG and EEG.2. 3D heart solid reconstruction based on CT imageThree-dimensional reconstruction of the heart used the chest CT images.This images spaced 1mm, and the total is 125. To simplify the later operation,all the images were preprocessing by Photoshop. The preprocessing increase the contrast of the CT image. And then we marked out the boundary of the heart by referencing to spectrum of a graph. The organizations division and three-dimensional reconstruction was finished in the Mimics software, the reconstructed model was saved as point cloud file. We imported the point cloud format file into the reverse engineering software Geomagic,and then edited the point cloud data into 3D reconstruction software, At last ,we finish the 3D solid heart model by modifying and editing the curved surfaces.The heart model is true and correct,it has a clear position in the three-dimensional coordinate system .It can be edited in the modeling software. Finally, we moved the heart model to the origin location.3. Electromagnetic field analysis of a 3D reconstruction heart based on FEAWe Introduced the basic principlesthe and steps of the finite element method analysis, described the tools software. Wethe analyzed the solving problem by he finite element method.At first, imported the heart model into tools software and established the model of the coil and the air.remeshed the whole model by the software integration of various sub-network function,set the different material properties, set the boundary conditions and driving function .At last we used the 3D solver to calculated the results and shown in post-processing.The result show the sphere of influence was close to the size of the coil projecting on surface area in the heart,the max intensity was 0.577T.Innovation points in this paper:1. In this paper, we analyzed the principle of a magnetic stimulation. According to the principle we designed the main circuit, and control circuit.The control circuit is based on the MSP430 The single-pulse magnetic stimulation which was degined meet the basic test requirements.2. We used tools soft to establishing the heart surface model, and then,used reverse engineering tools to establish a three-dimensional solid model of the heart. The heart model is true and correct, we can edit and changes the model and find the precise positioning in three dimensionscan3. Based on the three-dimensional entities heart model, the coil and air model.we got a finite element model,and then we calculated the electromagnetic field closed to the real situation when the magnetic stimulation was affecting the heart.更多还原