Department of Bioengineering, Stanford University, 443 Via Ortega, Stanford, CA, 94305, USA.
Department of Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN, 55905, USA.
Neuroimage. 2020 May 1;211:116592. doi: 10.1016/j.neuroimage.2020.116592. Epub 2020 Feb 1.
Magnetic resonance elastography (MRE) is emerging as a new tool for studying viscoelastic changes in the brain resulting from functional processes. Here, we demonstrate a novel time series method to generate robust functional magnetic resonance elastography (fMRE) activation maps in response to a visual task with a flashing checkerboard stimulus. Using a single-shot spin-echo (SS-SE) pulse sequence, the underlying raw images inherently contain blood-oxygen-level dependent (BOLD) contrast, allowing simultaneous generation of functional magnetic resonance imaging (fMRI) activation maps from the magnitude and functional magnetic resonance elastography (fMRE) maps from the phase. This allows an accurate comparison of the spatially localized stiffness (fMRE) and BOLD (fMRI) changes within a single scan, eliminating confounds inherent in separately acquired scans. Results indicate that tissue stiffness within the visual cortex increases 6-11% with visual stimuli, whereas the BOLD signal change was 1-2%. Furthermore, the fMRE and fMRI activation maps have strong spatial overlap within the visual cortex, providing convincing evidence that fMRE is possible in the brain. However, the fMRE temporal SNR (tSNR) maps are heterogeneous across the brain. Using a dictionary matching approach to characterize the time series, the viscoelastic changes are consistent with a viscoelastic response function (VRF) time constant of 12.1 s ± 3.0 s for a first-order exponential decay, or a shape parameter of 8.1 s ± 1.4 s for a gamma-variate.
磁共振弹性成像（MRE）作为一种研究大脑因功能过程引起的粘弹性变化的新工具正在兴起。在这里，我们展示了一种新的时间序列方法，用于生成响应闪烁棋盘刺激的视觉任务的稳健功能磁共振弹性成像（fMRE）激活图。使用单次激发自旋回波（SS-SE）脉冲序列，底层原始图像固有地包含血氧水平依赖（BOLD）对比，从而可以从幅度同时生成功能磁共振成像（fMRI）激活图和相位的功能磁共振弹性成像（fMRE）图。这允许在单次扫描中准确比较局部化刚度（fMRE）和 BOLD（fMRI）变化，消除分别采集扫描固有的混杂因素。结果表明，视觉皮层内的组织刚度随视觉刺激增加 6-11%，而 BOLD 信号变化为 1-2%。此外，fMRE 和 fMRI 激活图在视觉皮层内具有很强的空间重叠，提供了令人信服的证据表明 fMRE 在大脑中是可行的。然而，fMRE 的时间 SNR（tSNR）图在整个大脑中是不均匀的。使用字典匹配方法来描述时间序列，粘弹性变化与一阶指数衰减的粘弹性响应函数（VRF）时间常数 12.1 s ± 3.0 s 或伽马变量的形状参数 8.1 s ± 1.4 s 一致。
