MRI-based, wireless determination of the transfer function of a linear implant: Introduction of the transfer matrix
MRI-based, wireless determination of the transfer function of a linear implant: Introduction of the transfer matrix
复制标题
DOI：
10.1002/mrm.27218
复制
发表时间：
2018-12-01
影响因子：
3.3
通讯作者：
van den Berg, Cornelis A. T.
中科院分区：
文献类型：
--
作者：
Tokaya, Janot P.;Raaijmakers, Alexander J. E.;van den Berg, Cornelis A. T.
目的：我们介绍了传递矩阵（TM），使基于MR的无线传递函数（TF）的确定成为可能。TF是线性植入物射频安全性评估的植入物特定指标。TF将植入物上的入射切向电场与其尖端处的散射电场相关联，该散射电场通常控制局部加热。TM扩展了这一概念，并将入射切向电场与植入物中的电流分布相关联，从而表征沿着整个植入物的RF响应。TM被利用来测量TF与MRI没有硬件alteration.Theory和方法：一个模型的双和双传播衰减波经历多次反射，是用来推导TM的解析表达式。这允许通用植入物的TM的参数化，例如，（部分）绝缘的单根导线，在均匀介质中的几个未知数，同时描述TF。这些未知数可以确定与MRI使得有可能测量TM，因此，也TF.Results：TM是能够预测由于入射电场的感应电流，可以准确地参数化与有限数量的未知数。使用这种描述的TF是准确地确定（与皮尔逊相关系数R >= 0.9之间的测量和模拟）从MRI acquisition.Conclusion：TM使TF与MRI的测试通用植入物模型的测量。基于MR的方法不需要硬件改变，并且是无线的，因此使得TF确定在更现实的场景中是可想象的。
Purpose: We introduce the transfer matrix (TM) that makes MR-based wireless determination of transfer functions (TFs) possible. TFs are implant specific measures for RF-safety assessment of linear implants. The TF relates an incident tangential electric field on an implant to a scattered electric field at its tip that generally governs local heating. The TM extends this concept and relates an incident tangential electric field to a current distribution in the implant therewith characterizing the RF response along the entire implant. The TM is exploited to measure TFs with MRI without hardware alterations.Theory and Methods: A model of rightward and leftward propagating attenuated waves undergoing multiple reflections is used to derive an analytical expression for the TM. This allows parameterization of the TM of generic implants, e.g., (partially) insulated single wires, in a homogeneous medium in a few unknowns that simultaneously describe the TF. These unknowns can be determined with MRI making it possible to measure the TM and, therefore, also the TF.Results: The TM is able to predict an induced current due to an incident electric field and can be accurately parameterized with a limited number of unknowns. Using this description the TF is determined accurately (with a Pearson correlation coefficient R >= 0.9 between measurements and simulations) from MRI acquisitions.Conclusion: The TM enables measuring of TFs with MRI of the tested generic implant models. The MR-based method does not need hardware alterations and is wireless hence making TF determination in more realistic scenarios conceivable.