Danish Research Center for Magnetic Resonance, Center for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital, Hvidovre, Denmark.
Center for Magnetic Resonance, DTU Elektro, Technical University of Denmark, Kgs Lyngby, Denmark.
Magn Reson Med. 2018 Feb;79(2):748-760. doi: 10.1002/mrm.26727. Epub 2017 May 30.
Clinical use of magnetic resonance electrical impedance tomography (MREIT) still requires significant sensitivity improvements. Here, the measurement of the current-induced magnetic field (ΔB ) is improved using systematic efficiency analyses and optimization of multi-echo spin echo (MESE) and steady-state free precession free induction decay (SSFP-FID) sequences.
Considering T , T , and T2* relaxation in the signal-to-noise ratios (SNRs) of the MR magnitude images, the efficiency of MESE and SSFP-FID MREIT experiments, and its dependence on the sequence parameters, are analytically analyzed and simulated. The theoretical results are experimentally validated in a saline-filled homogenous spherical phantom with relaxation parameters similar to brain tissue. Measurement of ΔB is also performed in a cylindrical phantom with saline and chicken meat.
The efficiency simulations and experimental results are in good agreement. When using optimal parameters, ΔB can be reliably measured in the phantom even at injected current strengths of 1 mA or lower for both sequence types. The importance of using proper crusher gradient selection on the phase evolution in a MESE experiment is also demonstrated.
The efficiencies observed with the optimized sequence parameters will likely render in-vivo human brain MREIT feasible. Magn Reson Med 79:748-760, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
磁共振电阻抗断层成像（MREIT）的临床应用仍需要显著提高灵敏度。在这里，通过系统的效率分析和多回波自旋回波（MESE）和稳态自由进动无感应衰减（SSFP-FID）序列的优化，提高了电流感应磁场（ΔB）的测量。
考虑到 T1、T2*弛豫对磁共振幅度图像信噪比（SNR）的影响，对 MESE 和 SSFP-FID MREIT 实验的效率及其对序列参数的依赖性进行了分析和模拟。在与脑组织弛豫参数相似的充满盐水的均匀球形仿体中对理论结果进行了实验验证。还在含有盐水和鸡肉的圆柱形仿体中测量了 ΔB。
效率模拟和实验结果吻合良好。即使在两种序列类型下，注入电流强度为 1 mA 或更低时，使用最优参数也可以在仿体中可靠地测量 ΔB。还证明了在 MESE 实验中适当选择碎裂梯度对相位演化的重要性。
优化序列参数后的效率有望使活体人脑 MREIT 成为可能。磁共振医学 79:748-760, 2018。© 2017 国际磁共振学会。
