Magneto-Acoustic Effects in Imaging

描述(申请人提供)：本提案的主要目标是研究生物组织中电流上的磁力，并分析和开发利用这些“磁声”效应的新成像技术。在过去的二十年里，许多研究人员提出了磁声方法来成像电流和电导率，并提出磁力和由此产生的位移可能在磁共振成像中发挥作用。目前，实验是这一领域的主导理论，这一提议将提供一个广泛、统一的理论框架，这些实验方法可以在此基础上建立起来。这项研究涉及多个领域，包括生物电学、生物磁学和弹性。有五个具体目标。具体目标1：计算磁共振成像过程中洛伦兹力(磁场中的电流所受的力)引起的位移的大小和分布。洛伦兹力引起的位移被认为是一种成像神经动作电流的机制，这个目标将检验这种机制是否可能。具体目标2：确定磁感应磁声层析成像中各向异性的影响。这项技术已经被提出作为一种电导率成像的方法，但最初的研究只考虑了各向同性的组织。各向异性在磁声层析成像中起着至关重要的作用。具体目标3：从理论上分析电导率梯度与超声诱导洛伦兹力的关系。磁声成像的反面是由洛伦兹力产生的超声感应电压。这一目标将发展通用的数学技术，利用超声波成像神经和肌肉的动作电流。具体目标4：建立一个力学双域模型来分析心脏波前的洛伦兹力。电双域模型被广泛用于描述心脏组织的电特性。为此，将开发一个类似的组织力学性能模型，该模型考虑了细胞内空间、细胞外空间的弹性特性，以及它们通过细胞膜的耦合。具体目标5：计算心脏组织产生的磁场，并确定其在磁共振成像过程中的影响。许多研究人员一直在寻找一种方法，利用磁共振成像来检测神经动作电流。然而，与心脏产生的电流相比，神经产生的电流很小。在这个目的中，将计算心脏动作电位波前的MRI信号。所有这五个目标都是用理论和计算方法解决的，结果将与现有的实验数据进行比较。

DESCRIPTION (provided by applicant): The primary goal of this proposal is to study magnetic forces on electric currents in biological tissue, and to analyze and develop new imaging techniques that use these "magneto-acoustic" effects. In the last two decades, many researchers have proposed magneto-acoustic methods to image current and conductivity, and have suggested that magnetic forces and the resulting displacements may play a role in magnetic resonance imaging. At the moment, experiment is leading theory in this field, and this proposal will provide a broad, unified theoretical framework upon which these experimental methods can be built. The research draws upon a variety of fields, including bioelectricity, biomagnetism, and elasticity. There are five specific aims. Specific Aim 1: Calculate the magnitude and distribution of displacement caused by the Lorentz force (the force on a current in a magnetic field) during magnetic resonance imaging. Displacements caused by the Lorentz force has been proposed as a mechanism to image neural action currents, and this aim will examine if such a mechanism is possible. Specific Aim 2: Determine the effect of anisotropy during magneto-acoustic tomography with magnetic induction. This technique has been proposed as a way to image electrical conductivity, but initial studies considered only isotropic tissue. Anisotropy may play a crucial role in magnetoacoustic tomography. Specific Aim 3: Analyze theoretically the relationship between conductivity gradients and the ultrasonically-induced Lorentz force. The inverse of magneto-acoustic imaging is ultrasonically-induced voltages arising from the Lorentz force. This aim will develop general mathematical techniques to image action currents from nerve and muscle using ultrasound. Specific Aim 4: Develop a mechanical bidomain model to analyze the Lorentz force on cardiac wave fronts. The electrical bidomain model is widely used to represent the electrical properties of cardiac tissue. In this aim, a similar model will be developed for the mechanical properties of tissue, which accounts for the elastic properties of the intracellular space, the extracellular space, and their coupling through the cell membrane. Specific Aim 5: Compute the magnetic field produced by cardiac tissue, and determine its influence during magnetic resonance imaging. Many researchers have sought a way to use magnetic resonance imaging to detect neural action currents. However, the current produced by a nerve is small compared to the current produced by the heart. In this aim, the MRI signature of a cardiac action potential wave front will be calculated. All five of these aims are addressed using theoretical and computational methods, and the results will be compared to existing experimental data.