Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey.
Phys Med Biol. 2018 Feb 8;63(4):045001. doi: 10.1088/1361-6560/aaa732.
Magnetic resonance electrical properties tomography (MR-EPT), aiming at reconstructing the EP's at radio frequencies, uses the H field (both magnitude and phase) distribution within the object. One of the MR-EPT algorithms, cr-MREPT, accurately reconstructs the internal tissue boundaries, however, it faces an artifact which occurs at the regions where the convective field, [Formula: see text], [Formula: see text], has a low magnitude (at the noise level). This study aims to develop an artifact-free conductivity reconstruction by modifying the H field inside the region of interest (ROI), using multiple RF transmission techniques in MRI. An eight channel multi-transmit transverse electromagnetic array is used in two different drive configurations. The first drive is the standard volume excitation configuration where all ports are driven with the same magnitude and with 45° phase increment between adjacent channels. In the second drive, the drive voltage magnitude and phases for each of the eight drive ports are modified to generate a desired H distribution such that the low convective field region moves to another non-overlapping position. Finally, data from both drive experiments are simultaneously used to reconstruct EP's. Computer simulations using cylindrical phantoms and a brain model are conducted and it is shown that the low convective field artifact can be eliminated. It is further shown that it is not necessary to re-calculate the port drive RF voltage magnitude and phases for each patient. The implementation issues of this method are briefly discussed.
磁共振电阻抗断层成像术（MR-EPT）旨在重建射频下的 EP，它利用物体内部的 H 场（幅度和相位）分布。MR-EPT 算法之一的 cr-MREPT 可以准确重建内部组织边界，但它面临着一个伪影问题，该伪影出现在[Formula: see text]，[Formula: see text]的幅度较低（处于噪声水平）的区域。本研究旨在通过在感兴趣区域（ROI）内修改 H 场，使用 MRI 中的多种 RF 传输技术来开发无伪影的电导率重建。使用两个不同的驱动配置使用了一个八通道多发射横电磁阵列。第一个驱动是标准体积激励配置，其中所有端口都以相同的幅度驱动，并在相邻通道之间具有 45°的相位增量。在第二个驱动中，修改了八个驱动端口的驱动电压幅度和相位，以产生期望的 H 分布，使得低对流场区域移动到另一个非重叠位置。最后，同时使用来自两个驱动实验的数据来重建 EP。对圆柱模型和脑模型进行了计算机模拟，结果表明可以消除低对流场伪影。进一步表明，对于每个患者，不需要重新计算端口驱动 RF 电压幅度和相位。简要讨论了该方法的实施问题。
