Department of Radiology, Kyung Hee University Hospital, Dongdaemoon-gu, Seoul, South Korea.
Department of Biomedical Engineering, Undergraduate School, College of Electronics and Information, Kyung Hee University, Giheung-gu, Yongin-si, Gyeonggi-do, South Korea.
J Neurosci Methods. 2024 Dec;412:110288. doi: 10.1016/j.jneumeth.2024.110288. Epub 2024 Sep 19.
Although blood oxygen level-dependent (BOLD) functional MRI (fMRI) is a standard method, major BOLD signals primarily originate from intravascular sources. Magnetic resonance electrical properties tomography (MREPT)-based fMRI signals may provide additional insights into electrical activity caused by alterations in ion concentrations and mobilities.
This study aimed to investigate the neuronal response of conductivity during visual stimulation and compare it with BOLD.
A total of 30 young, healthy volunteers participated in two independent experiments using BOLD and MREPT techniques with a visual stimulation paradigm at 3 T MRI. The first set of MREPT fMRI data was obtained using a multi-echo spin-echo (SE) echo planar imaging (EPI) sequence from 14 participants. The second set of MREPT fMRI data was collected from 16 participants using both a single-echo SE-EPI and a single-echo three-dimensional (3D) balanced fast-field-echo (bFFE) sequence. We reconstructed the time-course Larmor frequency conductivity to evaluate hemodynamics.
Conductivity values slightly increased during visual stimulation. Activation strengths were consistently stronger with BOLD than with conductivity for both SE-EPI MREPT and bFFE MREPT. Additionally, the activated areas were always larger with BOLD than MREPT. Some participants also exhibited decreased conductivity values during visual stimulations. In Experiment 1, conductivity showed significant differences between the fixation and visual stimulation blocks in the secondary visual cortex (SVC) and cuneus, with conductivity differences of 0.43 % and 0.47 %, respectively. No significant differences in conductivity were found in the cerebrospinal fluid (CSF) areas between the two blocks. In Experiment 2, significant conductivity differences were observed between the two blocks in the SVC, cuneus, and lingual gyrus for SE-EPI MREPT, with differences of 0.90 %, 0.67 %, and 0.24 %, respectively. Again, no significant differences were found in the CSF areas.
Conductivity values increased slightly during visual stimulation in the visual cortex areas but were much weaker than BOLD responses. The conductivity change during visual stimulation was less than 1 % compared to the fixation block. No significant differences in conductivity were observed between the primary visual cortex (PVC)-CSF and SVC-CSF during fixation and visual stimulations, suggesting that the observed conductivity changes may not be related to CSF changes in the visual cortex but rather to diffusion changes. Future research should explore the potential of MREPT to detect neuronal electrical activity and hemodynamic changes, with further optimization of the MREPT technique.
尽管血氧水平依赖（BOLD）功能磁共振成像（fMRI）是一种标准方法，但主要的 BOLD 信号主要源自血管内源。基于磁共振电学特性层析成像（MREPT）的 fMRI 信号可能提供关于离子浓度和迁移率变化引起的电活动的额外见解。
本研究旨在探讨视觉刺激过程中电导率的神经元反应，并将其与 BOLD 进行比较。
在 3T MRI 上使用视觉刺激范式，共 30 名年轻健康志愿者参与了两项独立的 BOLD 和 MREPT 实验。第一组 MREPT fMRI 数据由 14 名参与者使用多回波自旋回波（SE）回波平面成像（EPI）序列获得。第二组 MREPT fMRI 数据由 16 名参与者使用单回波 SE-EPI 和单回波三维（3D）平衡快速场回波（bFFE）序列采集。我们重建了时程劳尔频率电导率以评估血液动力学。
在视觉刺激期间，电导率值略有增加。与 BOLD 相比，SE-EPI MREPT 和 bFFE MREPT 的激活强度始终更强。此外，BOLD 的激活区域总是大于 MREPT。一些参与者在视觉刺激期间也表现出电导率值下降。在实验 1 中，电导率在次级视觉皮层（SVC）和楔前叶的注视和视觉刺激块之间显示出显著差异，电导率差异分别为 0.43%和 0.47%。在两个块之间，CSF 区域的电导率没有发现显著差异。在实验 2 中，SE-EPI MREPT 中 SVC、楔前叶和舌回的两个块之间观察到显著的电导率差异，差异分别为 0.90%、0.67%和 0.24%。同样，在 CSF 区域未发现显著差异。
在视觉皮层区域，电导率值在视觉刺激期间略有增加，但比 BOLD 反应弱得多。与注视块相比，视觉刺激期间的电导率变化小于 1%。在注视和视觉刺激期间，初级视觉皮层（PVC）-CSF 和 SVC-CSF 之间的电导率没有观察到显著差异，这表明观察到的电导率变化可能与视觉皮层中的 CSF 变化无关，而与扩散变化有关。未来的研究应探索 MREPT 检测神经元电活动和血液动力学变化的潜力，并进一步优化 MREPT 技术。
