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

项目摘要/摘要 目前最新的肿瘤切除术前无创计划是进行基于任务的血液 氧水平依赖(BOLD)功能磁共振成像(FMRI)。在扫描过程中，一名患者 执行特定任务以定位与该任务相关的大脑功能区。BOLD功能磁共振检测到 脱氧血红蛋白浓度受神经元活动时发生的血液动力学因素的影响。 依赖大胆的信号来代表大脑的活动是有局限性的。一个主要的限制是 使用BOLD fMRI的脑激活图依赖于血流动力学变化和脑功能成像之间的紧密耦合 神经元活动。在脑肿瘤或其他脑局灶性病变存在的情况下，神经元之间的耦合 发生在邻近血管系统的活动和血流动力学变化经常被破坏，这是指 作为神经血管解偶联(NVU)。NVU是解释基于任务的BOLD功能磁共振成像的主要问题 脑局灶性病变环境中的MAP，因为它可能导致假想的激活减少或甚至缺失 电活动的，基本功能的皮质。因此，口才皮质的外科切除可能发生在 由此导致的术后发病率。BOLD功能磁共振成像的另一个局限性，由于其间接测量神经元活动， 在启动和停止血流动力学反应方面都有几秒钟的偏移 神经活动的实际时间。大胆的fMRI反应的时间轮廓中的这种滞后变得更多 在脑瘤的情况下很关键。因此，这种大胆的信号很容易受到“血流动力学调节”的影响。 这降低了粗体信号的空间和时间精度。要克服这些大胆的限制 功能磁共振成像是一种对血流动力学变化免疫的方法，更直接地反映了神经活动 是必要的。一种有希望的替代方法是使用与激活相关的大脑表观减少 磁共振弥散加权成像(DWI)测量扩散常数(ADC)。磁共振弥散加权成像在功能成像中的应用 被称为扩散加权功能磁共振成像(DfMRI)。弥散加权成像对脑内下层组织的水分扩散敏感。 先前的工作表明，大脑中激活的皮质区域的ADC减少，发生在几秒钟前 用BOLD功能磁共振成像检测血流动力学反应。因此，这些观察结果表明，dfmri 与传统的BOLD功能磁共振成像相比，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，还没有关于dfmri在评估脑血管疾病方面的研究。 脑瘤患者。在目前的提案中，我们的目标是在存在脑损伤的情况下研究dfMRI- 导致神经元活动和血流动力学变化之间的耦合中断。我们假设dfMRI 可以提高对大脑病变附近初级运动皮质激活的检测能力。

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.