Department of Electrical Engineering and Information Technology, Institute of Biomedical Engineering, Karlsruhe Institute of Technology, Karlsruhe, Germany.
Magn Reson Med. 2011 Aug;66(2):456-66. doi: 10.1002/mrm.22832. Epub 2011 Feb 24.
The electric properties of human tissue can potentially be used as an additional diagnostic parameter, e.g., in tumor diagnosis. In the framework of radiofrequency safety, the electric conductivity of tissue is needed to correctly estimate the local specific absorption rate distribution during MR measurements. In this study, a recently developed approach, called electric properties tomography (EPT) is adapted for and applied to in vivo imaging. It derives the patient's electric conductivity and permittivity from the spatial sensitivity distributions of the applied radiofrequency coils. In contrast to other methods to measure the patient's electric properties, EPT does not apply externally mounted electrodes, currents, or radiofrequency probes, which enhances the practicability of the approach. This work shows that conductivity distributions can be reconstructed from phase images and permittivity distributions can be reconstructed from magnitude images of the radiofrequency transmit field. Corresponding numerical simulations using finite-difference time-domain methods support the feasibility of this phase-based conductivity imaging and magnitude-based permittivity imaging. Using this approximation, three-dimensional in vivo conductivity and permittivity maps of the human brain are obtained in 5 and 13 min, respectively, which can be considered a step toward clinical feasibility for EPT.
人体组织的电学特性可作为额外的诊断参数，例如用于肿瘤诊断。在射频安全的框架内，需要组织的电导率来正确估计磁共振测量过程中的局部比吸收率分布。在这项研究中，最近开发的一种方法，称为电特性层析成像（EPT），被用于体内成像。它从应用的射频线圈的空间灵敏度分布中推导出患者的电导率和介电常数。与其他测量患者电特性的方法不同，EPT 不使用外部电极、电流或射频探头，这提高了该方法的实用性。这项工作表明，电导率分布可以从相位图像重建，介电常数分布可以从射频发射场的幅度图像重建。使用时域有限差分方法的相应数值模拟支持基于相位的电导率成像和基于幅度的介电常数成像的可行性。使用此近似，分别在 5 分钟和 13 分钟内获得了人体大脑的三维体内电导率和介电常数图，这可以被认为是 EPT 向临床可行性迈出的一步。
