Department of Mathematics, Konkuk University, Seoul, Korea.
Phys Med Biol. 2010 May 7;55(9):2743-59. doi: 10.1088/0031-9155/55/9/021. Epub 2010 Apr 19.
The aim of magnetic resonance electrical impedance tomography (MREIT) is to visualize the electrical properties, conductivity or current density of an object by injection of current. Recently, the prolonged data acquisition time when using the injected current nonlinear encoding (ICNE) method has been advantageous for measurement of magnetic flux density data, Bz, for MREIT in the signal-to-noise ratio (SNR). However, the ICNE method results in undesirable side artifacts, such as blurring, chemical shift and phase artifacts, due to the long data acquisition under an inhomogeneous static field. In this paper, we apply the ICNE method to a gradient and spin echo (GRASE) multi-echo train pulse sequence in order to provide the multiple k-space lines during a single RF pulse period. We analyze the SNR of the measured multiple B(z) data using the proposed ICNE-Multiecho MR pulse sequence. By determining a weighting factor for B(z) data in each of the echoes, an optimized inversion formula for the magnetic flux density data is proposed for the ICNE-Multiecho MR sequence. Using the ICNE-Multiecho method, the quality of the measured magnetic flux density is considerably increased by the injection of a long current through the echo train length and by optimization of the voxel-by-voxel noise level of the B(z) value. Agarose-gel phantom experiments have demonstrated fewer artifacts and a better SNR using the ICNE-Multiecho method. Experimenting with the brain of an anesthetized dog, we collected valuable echoes by taking into account the noise level of each of the echoes and determined B(z) data by determining optimized weighting factors for the multiply acquired magnetic flux density data.
磁共振电阻抗断层成像（MREIT）的目的是通过注入电流来可视化物体的电特性、电导率或电流密度。最近，在使用注入电流非线性编码（ICNE）方法时，由于在非均匀静态场下进行长时间的数据采集，有利于测量磁通量密度数据 Bz，从而提高 MREIT 的信噪比（SNR）。然而，由于长时间的数据采集，ICNE 方法会导致不理想的侧方伪影，如模糊、化学位移和相位伪影。在本文中，我们将 ICNE 方法应用于梯度和自旋回波（GRASE）多回波 train 脉冲序列，以便在单个 RF 脉冲周期内提供多个 k 空间线。我们分析了使用所提出的 ICNE-Multiecho MR 脉冲序列测量的多个 B(z)数据的 SNR。通过确定每个回波中 B(z)数据的权重因子，我们为 ICNE-Multiecho MR 序列提出了一种优化的磁通密度数据反演公式。通过在回波 train 长度内注入长电流并优化体素级 B(z)值的噪声水平，ICNE-Multiecho 方法可以显著提高测量磁通量密度的质量。使用 ICNE-Multiecho 方法进行琼脂糖凝胶体模实验，证明了较少的伪影和更好的 SNR。在麻醉犬大脑的实验中，我们考虑了每个回波的噪声水平，通过确定优化的权重因子来收集有价值的回声，并确定了通过多次采集的磁通密度数据的优化权重因子。
