Diffusion-weighted fMRI for presurgical mapping of primary motor cortex in the presence of neurovascular uncoupling (NVU)

项目概要/摘要 目前最先进的术前无创规划肿瘤切除术是执行基于任务的血液 氧水平依赖（BOLD）功能性磁共振成像（fMRI）。在扫描过程中，患者 执行特定任务以定位与该任务相关的脑功能区域。BOLD功能磁共振成像检测 脱氧血红蛋白浓度受血液动力学因素的影响，这些因素是对神经元活动的反应。 依赖BOLD信号来表示大脑活动具有局限性。一个主要的限制是， 使用BOLD功能磁共振成像的大脑激活映射依赖于血液动力学变化和 神经元活动在存在脑肿瘤或其他局灶性脑病变的情况下，神经元之间的偶联可能是不稳定的。 活动和血流动力学的变化发生在邻近的脉管系统往往是中断，这是指 神经血管解偶联（NVU）。NVU是基于任务的BOLD fMRI解释中的一个主要问题 在局灶性脑损伤的情况下，因为它可能会导致假性减少，甚至没有激活， 电活性的基本功能皮层因此，功能区皮质的手术切除可能会发生， 导致术后发病率。BOLD功能磁共振成像的另一个局限性是，由于它间接测量神经元活动， 在血液动力学响应的开始和停止中存在几秒的偏移， 神经活动的实际时间BOLD功能磁共振成像反应的时间曲线的这种滞后变得更加明显。 这对脑瘤来说至关重要。因此，BOLD信号易受“血液动力学调制”的影响。 这降低了BOLD信号的空间和时间精度。为了克服BOLD的这些局限性， fMRI是一种不受血流动力学变化影响、更直接反映神经活动的方法 是必要的。一种有希望的替代方法是使用与激活相关的脑表观 采用扩散加权MRI（DWI）观察扩散常数（ADC）。DWI在功能成像中的应用 称为“弥散加权功能磁共振成像（dfMRI）”。DWI对脑内下层组织的水扩散敏感。 先前的研究表明，大脑ADC在激活的皮层区域减少，发生在大脑激活前几秒。 BOLD fMRI检测血流动力学反应。因此，这些观察结果表明，dfMRI是更多 与传统的BOLD fMRI相比，它与大脑激活直接相关，而且可能独立于 血流动力学反应因子然而，到目前为止，还没有dfMRI在评估 脑肿瘤患者。在目前的建议中，我们的目标是研究dfMRI在脑损伤的存在- 诱导神经元活动和血液动力学变化之间的耦合中断。我们假设dfMRI 可以增强脑损伤附近的初级运动皮层激活的可检测性。

Project Summary/Abstract Current state-of-art for preoperative noninvasive planning of tumor resection is to perform task-based blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI). During scanning, a patient performs a specific task to localize brain functional regions related to the task. BOLD fMRI detects alterations in deoxyhemoglobin concentration influenced by hemodynamic factors that occur in response to neuronal activity. The reliance on BOLD signal to represent activity in the brain comes with limitations. One major limitation is that brain activation mapping using BOLD fMRI relies on the tight coupling between hemodynamic changes and neuronal activity. In the presence of brain tumors or other focal brain lesions, the coupling between neuronal activity and the hemodynamic changes occurring in the adjacent vasculature is often disrupted, which is referred as neurovascular uncoupling (NVU). NVU is a major problem in the interpretation of task-based BOLD fMRI maps in the settings of focal brain lesions, as it may lead to spuriously decreased or even absent activation in electrically active, essential functional cortex. As a result, surgical resection of eloquent cortex may occur with resultant postsurgical morbidity. Another limitation of BOLD fMRI, due to its indirect measure of neuronal activity, is that there is a several second offset in both initiation and cessation of the hemodynamic response with respect to actual timing of neural activity. Such a lag in the temporal profile of the BOLD fMRI response becomes more critical in the case of brain tumors. As a result, the BOLD signal is susceptible to “hemodynamic modulations” which decreases the spatial and temporal accuracy of the BOLD signal. To overcome these limitations of BOLD fMRI, a method which is immune to the hemodynamic changes and is more direct representation of neural activity is needed. A promising alternative approach is the use of activation-associated decreases in brain apparent diffusion constant (ADC) observed using diffusion-weighted MRI (DWI). The use of DWI for functional imaging is referred as ‘diffusion-weighted fMRI (dfMRI)’. DWI is sensitized to water diffusion of underlying tissues in brain. Prior work has shown that brain ADC decreases in activated cortical areas, occurring several seconds before the hemodynamic response detected by BOLD fMRI. These observations therefore suggest that dfMRI is more directly linked to brain activation than traditional BOLD fMRI, and furthermore may be independent of hemodynamic response factors. However, to date there have been no studies of dfMRI in the evaluation of patients with brain tumors. In the current proposal, we aim to investigate dfMRI in the presence of brain lesion- induced disruption of coupling between neuronal activity and hemodynamic changes. We hypothesize that dfMRI may enhance detectability of primary motor cortex activation in the vicinity of brain lesions.