Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455 USA.
IEEE Trans Med Imaging. 2010 Feb;29(2):474-81. doi: 10.1109/TMI.2009.2036843.
The electric properties (EPs) of biological tissue, i.e., the electric conductivity and permittivity, can provide important information in the diagnosis of various diseases. The EPs also play an important role in specific absorption rate calculation, a major concern in high-field MRI, as well as in nonmedical areas such as wireless telecommunications. The high-field MRI system is accompanied by significant wave propagation effects, and the RF radiation is dependent on the EPs of biological tissue. On the basis of the measurement of the active transverse magnetic component of the applied RF field (known as B(1)-mapping technique), we propose a dual-excitation algorithm, which uses two sets of measured B(1) data to noninvasively reconstruct the EPs of biological tissues. The finite-element method was utilized in 3-D modeling and B(1) field calculation. A series of computer simulations were conducted to evaluate the feasibility and performance of the proposed method on a 3-D head model within a TEM coil and a birdcage coil. Using a TEM coil, when noise free, the reconstructed EP distribution of tissues in the brain has relative errors of 12%-28% and correlated coefficients of greater than 0.91. Compared with other B(1)-mapping-based reconstruction algorithms, our approach provides superior performance without the need for iterative computations. The present simulation results suggest that good reconstruction of EPs from B1 mapping can be achieved.
生物组织的电学特性（EPs），即电导率和介电常数，可以提供各种疾病诊断的重要信息。EPs 在特定吸收率计算中也起着重要作用，这是高场 MRI 的一个主要关注点，同时也在无线电信等非医疗领域发挥着重要作用。高场 MRI 系统伴随着显著的波传播效应，RF 辐射取决于生物组织的 EPs。在测量应用 RF 场的主动横向磁场分量（称为 B(1)-映射技术）的基础上，我们提出了一种双激发算法，该算法使用两组测量的 B(1)数据来无创重建生物组织的 EPs。在 3-D 建模和 B(1)场计算中使用了有限元方法。在 TEM 线圈和鸟笼线圈内的 3-D 头部模型上进行了一系列计算机模拟，以评估所提出方法的可行性和性能。使用 TEM 线圈，当无噪声时，大脑中组织的重建 EP 分布的相对误差为 12%-28%，相关系数大于 0.91。与其他基于 B(1)-映射的重建算法相比，我们的方法无需迭代计算即可提供更好的性能。目前的模拟结果表明，从 B1 映射可以很好地重建 EPs。
