Seifert Alan C, Xu Junqian, Kong Yazhuo, Eippert Falk, Miller Karla L, Tracey Irene, Vannesjo S Johanna
Biomedical Engineering and Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
Department of Diagnostic, Molecular, and Interventional Radiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
Hum Brain Mapp. 2024 Feb 15;45(3):e26597. doi: 10.1002/hbm.26597.
Although functional magnetic resonance imaging (fMRI) is widely applied in the brain, fMRI of the spinal cord is more technically demanding. Proximity to the vertebral column and lungs results in strong spatial inhomogeneity and temporal fluctuations in B . Increasing field strength enables higher spatial resolution and improved sensitivity to blood oxygenation level-dependent (BOLD) signal, but amplifies the effects of B inhomogeneity. In this work, we present the first task fMRI in the spinal cord at 7 T. Further, we compare the performance of single-shot and multi-shot 2D echo-planar imaging (EPI) protocols, which differ in sensitivity to spatial and temporal B inhomogeneity. The cervical spinal cords of 11 healthy volunteers were scanned at 7 T using single-shot 2D EPI at 0.75 mm in-plane resolution and multi-shot 2D EPI at 0.75 and 0.6 mm in-plane resolutions. All protocols used 3 mm slice thickness. For each protocol, the BOLD response to 13 10-s noxious thermal stimuli applied to the right thumb was acquired in a 10-min fMRI run. Image quality, temporal signal to noise ratio (SNR), and BOLD activation (percent signal change and z-stat) at both individual- and group-level were evaluated between the protocols. Temporal SNR was highest in single-shot and multi-shot 0.75 mm protocols. In group-level analyses, activation clusters appeared in all protocols in the ipsilateral dorsal quadrant at the expected C6 neurological level. In individual-level analyses, activation clusters at the expected level were detected in some, but not all subjects and protocols. Single-shot 0.75 mm generally produced the highest mean z-statistic, while multi-shot 0.60 mm produced the best-localized activation clusters and the least geometric distortion. Larger than expected within-subject segmental variation of BOLD activation along the cord was observed. Group-level sensory task fMRI of the cervical spinal cord is feasible at 7 T with single-shot or multi-shot EPI. The best choice of protocol will likely depend on the relative importance of sensitivity to activation versus spatial localization of activation for a given experiment. PRACTITIONER POINTS: First stimulus task fMRI results in the spinal cord at 7 T. Single-shot 0.75 mm 2D EPI produced the highest mean z-statistic. Multi-shot 0.60 mm 2D EPI provided the best-localized activation and least distortion.
尽管功能磁共振成像（fMRI）在脑部已得到广泛应用，但脊髓的fMRI在技术上要求更高。由于靠近脊柱和肺部，会导致磁场（B）出现强烈的空间不均匀性和时间波动。提高场强可实现更高的空间分辨率，并提高对血氧水平依赖（BOLD）信号的敏感性，但会放大B不均匀性的影响。在这项研究中，我们展示了首例在7T磁场下的脊髓任务fMRI。此外，我们比较了单次激发和多次激发二维回波平面成像（EPI）协议的性能，这两种协议对空间和时间B不均匀性的敏感性有所不同。对11名健康志愿者的颈脊髓在7T磁场下进行扫描，使用了平面分辨率为0.75mm的单次激发二维EPI以及平面分辨率为0.75mm和0.6mm的多次激发二维EPI。所有协议均采用3mm的层厚。对于每个协议，在10分钟的fMRI扫描过程中采集对施加于右手拇指的13次10秒有害热刺激的BOLD反应。在各协议之间评估了个体和组水平的图像质量、时间信噪比（SNR）以及BOLD激活（信号变化百分比和z统计量）。单次激发和0.75mm的多次激发协议的时间SNR最高。在组水平分析中，激活簇出现在所有协议中预期的C6神经水平的同侧背侧象限。在个体水平分析中，在部分但并非所有受试者和协议中检测到了预期水平的激活簇。单次激发0.75mm通常产生最高的平均z统计量，而多次激发0.60mm产生定位最佳的激活簇且几何畸变最小。观察到沿脊髓的BOLD激活在受试者内的节段变化大于预期。在7T磁场下，使用单次激发或多次激发EPI进行颈脊髓的组水平感觉任务fMRI是可行的。对于给定的实验，协议的最佳选择可能取决于对激活的敏感性与激活的空间定位的相对重要性。从业者要点：首例7T磁场下脊髓刺激任务fMRI结果。单次激发0.75mm二维EPI产生最高的平均z统计量。多次激发0.60mm二维EPI提供定位最佳的激活且畸变最小。
