Nair Veena A, Raut Ryan V, Prabhakaran Vivek
Department of Radiology, University of Wisconsin-Madison, Madison, WI, United States.
Neuroscience Training Program, University of Wisconsin-Madison, Madison, WI, United States.
Front Neurol. 2017 Jun 19;8:283. doi: 10.3389/fneur.2017.00283. eCollection 2017.
Blood oxygenation level-dependent (BOLD) functional MRI (fMRI) has been extensively used as a marker of brain dysfunction and subsequent recovery following stroke. However, growing evidence suggests that straightforward interpretation of BOLD fMRI changes with aging and disease is challenging. In this study, we investigated the effect of calibrating task fMRI data by applying a hemodynamic calibration method using the resting-state fluctuation amplitude (RSFA). Task fMRI responses were obtained during a covert verbal fluency task in a group of early stage stroke patients and matched healthy normal controls.
Fifteen acute left hemisphere stroke patients (less than 7 days from stroke; aged 44-84 years, average ~64 years) and 21 healthy controls (aged 55-77 years, average ~61 years) were prospectively studied. All subjects completed a 3-min covert verbal fluency task, and a 10-min eyes-closed resting-state fMRI scan, from which the calibration factor (RSFA) was computed. A behavioral measure on the verbal fluency task was also collected outside the scanner. Whole brain activation volumes and region-of-interest (ROI)-wise percent signal change and activation volumes before and after calibration were computed.
Between-group differences in whole brain activation volumes, although statistically significant before calibration failed to be significant after calibration. There were significant within-group differences before and after calibration with RSFA. Statistically significant between-group differences on ROI-wise measures before calibration also significantly reduced after calibration. Exploratory brain-behavior correlations revealed a similar pattern: significant correlations before calibration failed to survive after calibration.
BOLD fMRI changes with aging and disease is confounded by changes in neurofunctional coupling leading to challenges in the straightforward interpretation of task fMRI results. Application of the hemodynamic calibration using the RSFA technique in the current study appeared to mitigate any differences between stroke and age-matched healthy controls. Our study indicates that estimating neural activity after applying hemodynamic scaling is important for studies of aging and for studies tracking post-stroke changes. We recommend that further investigation of hemodynamic calibration with RSFA in healthy subjects and in stroke in larger samples is necessary.
血氧水平依赖（BOLD）功能磁共振成像（fMRI）已被广泛用作中风后脑功能障碍及后续恢复的标志物。然而，越来越多的证据表明，直接解读BOLD fMRI随衰老和疾病的变化具有挑战性。在本研究中，我们通过应用基于静息态波动幅度（RSFA）的血流动力学校准方法来研究校准任务fMRI数据的效果。在一组早期中风患者和相匹配的健康正常对照者进行隐蔽言语流畅性任务期间获取任务fMRI反应。
前瞻性研究了15例急性左半球中风患者（中风后不到7天；年龄44 - 84岁，平均约64岁）和21名健康对照者（年龄55 - 77岁，平均约61岁）。所有受试者完成一项3分钟的隐蔽言语流畅性任务以及一次10分钟的闭眼静息态fMRI扫描，从中计算校准因子（RSFA）。还在扫描器外收集了关于言语流畅性任务的行为测量数据。计算了校准前后全脑激活体积、感兴趣区域（ROI）层面的信号变化百分比和激活体积。
校准前全脑激活体积的组间差异虽具有统计学意义，但校准后不再显著。使用RSFA校准前后组内存在显著差异。校准前ROI层面测量的组间统计学显著差异在校准后也显著降低。探索性脑 - 行为相关性显示出类似模式：校准前的显著相关性在校准后不再存在。
BOLD fMRI随衰老和疾病的变化因神经功能耦合的变化而混淆，导致直接解读任务fMRI结果具有挑战性。在本研究中应用基于RSFA技术的血流动力学校准似乎减轻了中风患者与年龄匹配的健康对照者之间的任何差异。我们的研究表明，应用血流动力学缩放后估计神经活动对于衰老研究和追踪中风后变化的研究很重要。我们建议有必要在更大样本的健康受试者和中风患者中进一步研究基于RSFA的血流动力学校准。
