Center for Magnetic Resonance Research (CMRR), Department of Radiology, University of Minnesota, USA.
Center for Magnetic Resonance Research (CMRR), Department of Radiology, University of Minnesota, USA.
Neuroimage. 2019 Apr 1;189:847-869. doi: 10.1016/j.neuroimage.2019.02.006. Epub 2019 Feb 5.
Advances in hardware, pulse sequences, and reconstruction techniques have made it possible to perform functional magnetic resonance imaging (fMRI) at sub-millimeter resolution while maintaining high spatial coverage and acceptable signal-to-noise ratio. Here, we examine whether sub-millimeter fMRI can be used as a routine method for obtaining accurate measurements of fine-scale local neural activity. We conducted fMRI in human visual cortex during a simple event-related visual experiment (7 T, gradient-echo EPI, 0.8-mm isotropic voxels, 2.2-s sampling rate, 84 slices), and developed analysis and visualization tools to assess the quality of the data. Our results fall along three lines of inquiry. First, we find that the acquired fMRI images, combined with appropriate surface-based processing, provide reliable and accurate measurements of fine-scale blood oxygenation level dependent (BOLD) activity patterns. Second, we show that the highly folded structure of cortex causes substantial biases on spatial resolution and data visualization. Third, we examine the well-recognized issue of venous contributions to fMRI signals. In a systematic assessment of large sections of cortex measured at a fine scale, we show that time-averaged T*-weighted EPI intensity is a simple, robust marker of venous effects. These venous effects are unevenly distributed across cortex, are more pronounced in gyri and outer cortical depths, and are, to a certain degree, in consistent locations across subjects relative to cortical folding. Furthermore, we show that these venous effects are strongly correlated with BOLD responses evoked by the experiment. We conclude that sub-millimeter fMRI can provide robust information about fine-scale BOLD activity patterns, but special care must be exercised in visualizing and interpreting these patterns, especially with regards to the confounding influence of the brain's vasculature. To help translate these methodological findings to neuroscience research, we provide practical suggestions for both high-resolution and standard-resolution fMRI studies.
硬件、脉冲序列和重建技术的进步使得在保持高空间覆盖和可接受的信噪比的同时，以亚毫米分辨率进行功能磁共振成像（fMRI）成为可能。在这里，我们研究了亚毫米 fMRI 是否可以作为一种常规方法，用于获得精细局部神经活动的准确测量。我们在人类视觉皮层中进行了简单的事件相关视觉实验的 fMRI（7T、梯度回波 EPI、0.8 毫米各向同性体素、2.2 秒采样率、84 个切片），并开发了分析和可视化工具来评估数据质量。我们的结果沿着三条探究线进行。首先，我们发现，获得的 fMRI 图像与适当的基于表面的处理相结合，可以提供可靠和准确的精细尺度血氧水平依赖（BOLD）活动模式的测量。其次，我们表明，皮层的高度折叠结构会对空间分辨率和数据可视化产生实质性偏差。第三，我们研究了静脉对 fMRI 信号贡献的公认问题。在对以精细尺度测量的大片皮层进行的系统评估中，我们表明，时间平均 T*-加权 EPI 强度是静脉效应的简单、稳健的标志物。这些静脉效应在皮层中分布不均匀，在脑回和外皮层深度更为明显，并且在一定程度上相对于皮层折叠在受试者之间的位置一致。此外，我们表明这些静脉效应与实验引起的 BOLD 反应强烈相关。我们得出结论，亚毫米 fMRI 可以提供关于精细尺度 BOLD 活动模式的稳健信息，但在可视化和解释这些模式时必须特别小心，尤其是要考虑到大脑血管的混杂影响。为了将这些方法学发现转化为神经科学研究，我们为高分辨率和标准分辨率 fMRI 研究提供了实用建议。
