Göksu Cihan, Scheffler Klaus, Gregersen Fróði, Eroğlu Hasan H, Heule Rahel, Siebner Hartwig R, Hanson Lars G, Thielscher Axel
Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital-Amager and Hvidovre, Copenhagen, Denmark.
High-Field Magnetic Resonance Center, Max-Planck-Institute for Biological Cybernetics, Tübingen, Germany.
Magn Reson Med. 2021 Dec;86(6):3131-3146. doi: 10.1002/mrm.28944. Epub 2021 Aug 1.
Magnetic resonance current-density imaging (MRCDI) combines MRI with low-intensity transcranial electrical stimulation (TES; 1-2 mA) to map current flow in the brain. However, usage of MRCDI is still hampered by low measurement sensitivity and image quality.
Recently, a multigradient-echo-based MRCDI approach has been introduced that presently has the best-documented efficiency. This MRCDI approach has now been advanced in three directions and has been validated by phantom and in vivo experiments. First, the importance of optimum spoiling for brain imaging was verified. Second, the sensitivity and spatial resolution were improved by using acquisition weighting. Third, navigators were added as a quality control measure for tracking physiological noise. Combining these advancements, the optimized MRCDI method was tested by using 1 mA TES for two different injection profiles.
For a session duration of 4:20 min, the new MRCDI method was able to detect TES-induced magnetic fields at a sensitivity level of 84 picotesla, representing a twofold efficiency increase against our original method. A comparison between measurements and simulations based on personalized head models showed a consistent increase in the coefficient of determination of ΔR = 0.12 for the current-induced magnetic fields and ΔR = 0.22 for the current flow reconstructions. Interestingly, some of the simulations still clearly deviated from the measurements despite the strongly improved measurement quality. This highlights the utility of MRCDI to improve head models for TES simulations.
The achieved sensitivity improvement is an important step from proof-of-concept studies toward a broader application of MRCDI in clinical and basic neuroscience research.
磁共振电流密度成像（MRCDI）将磁共振成像（MRI）与低强度经颅电刺激（TES；1 - 2毫安）相结合，以绘制大脑中的电流流动情况。然而，MRCDI的使用仍受到测量灵敏度低和图像质量差的阻碍。
最近，一种基于多梯度回波的MRCDI方法被引入，目前该方法具有最充分的文献记录证明其效率。这种MRCDI方法现已在三个方向上得到改进，并已通过体模和体内实验得到验证。首先，验证了最佳扰相技术对脑成像的重要性。其次，通过使用采集加权提高了灵敏度和空间分辨率。第三，添加导航器作为跟踪生理噪声的质量控制措施。结合这些改进，使用1毫安的TES针对两种不同的注入模式对优化后的MRCDI方法进行了测试。
对于4:20分钟的扫描时长，新的MRCDI方法能够以84皮特斯拉的灵敏度检测到TES诱发的磁场，相较于我们原来的方法，效率提高了两倍。基于个性化头部模型的测量与模拟之间的比较表明，对于电流诱发磁场，决定系数一致提高了ΔR = （此处原文可能有误，推测为0.12），对于电流流动重建，决定系数提高了ΔR = （此处原文可能有误，推测为0.22）。有趣的是，尽管测量质量有了显著提高，但一些模拟结果仍明显偏离测量值。这突出了MRCDI在改进用于TES模拟的头部模型方面的作用。
所实现的灵敏度提高是从概念验证研究迈向MRCDI在临床和基础神经科学研究中更广泛应用的重要一步。
