BIOPHYSICAL BASIS OF FUNCTIONAL BRAIN MRI

本建议旨在加深对这些机制的了解， 参与大脑的功能性MRI，并优化成像和数据 用于检测神经元活动的分析策略。 功能性MRI 依赖于检测产生的NMR信号变化的能力 在皮层的离散区域响应特定的激活刺激， 并且被认为反映了局部血流、体积和 氧合 功能性磁共振成像有望成为这些方法的主要补充 可用于研究大脑活动。 尽管人们普遍认为 该方法的力量和成功，仍然有几个没有答案 关于其最佳使用模式、组织和技术 确定检测到的信号变化的重要因素，以及 这些信号变化的意义和解释。 研究 建议将系统地解决这些问题。 底层 机制可能包括磁化率对比效应，基于 粗体效果，以及洗入效果，这些将分别 量化。 影响每个机制的因素将分别 识别和测量。 对于BOLD效应，广泛的计算机建模 在幻影和动物大脑中的测量将用于建立 对不同尺寸的血管结构的相对敏感性， 间距和方向，以及其他组织特性，例如 水的扩散速度。 对s的单独敏感性称为静电 场效应（T2*）、扩散损失和其他机制也将被 确立了习 将比较不同脉冲序列的性能 设计1.5T下的最佳扫描和检测方法。 回波平面 成像、常规梯度回波和快速自旋回波成像以及 更多新颖的方案将在幻影、动物大脑和实例中进行比较 人类活动。 人体和动物的激活将在体内产生 利用视觉和运动刺激以及通过改变整体血液 乙酰唑胺和高碳酸血症 电流的一个重要特征 检测激活的范例是数据分析方法， 与任务的性质和所使用的成像方法相关。 我们将 比较分析功能数据集的不同方法，包括 统计参数映射、时间相关性分析和主成分分析 成分分析 每一个对运动和其他伪影的灵敏度 将通过体内比较和计算机模拟来建立。 从这些研究中，我们预计能够改善战略， 功能磁共振成像在人类功能研究中的应用和解释， 认知.

This proposal aims to develop an improved understanding of the mechanisms involved in functional MRI of the brain and to optimize imaging and data analysis strategies for the detection of neuronal activity. Functional MRI relies on the ability to detect the changes in NMR signal that are produced in discrete regions of cortex in response to specific activating stimuli, and are believed to reflect changes in local blood flow, volume and oxygenation. Functional MRI promises to be a major addition to the methods available for studying brain activation. Despite the widespread claims for the power and successes of the method, there remain several unanswered questions regarding its optimal mode of use, the tissue and technical factors that are important in determining the signal changes detected, and the significance and interpretation of these signal changes. The research proposed would systematically address such issues. The underlying mechanism may include both susceptibility contrast effects, based on the BOLD effect, as well as wash-in effects, and these will be separately quantified. The factors that affect each mechanism will be separately identified and measured. For the BOLD effect, extensive computer modeling and measurements in phantoms and animals brains will be used to establish the relative sensitivity to vascular structures of different sizes, spacings and orientations, as well as other tissue properties such as the rate of water diffusion. The separate sensitivities to s-called static field effects (T2*), diffusive losses and other mechanisms will also be established. The performance of different pulse sequences will be compared to devise optimal methods of scanning and detection at 1.5T. Echo planar imaging, conventional gradient echo and fast spin echo imaging as well as more novel schemes will be compared in phantoms, animal brains and examples of human activation. Human and animal activations will be produced in vivo using visual and motor stimuli as well as by alteration of global blood flow by acetazolamide and hypercarbia. A critical feature of current paradigms for detecting activation is the method of data analysis, which is interrelated with the nature of the task and imaging method used. We will compare different methods of analyzing functional data sets, including statistical parameter mapping, time-correlation analyses, and principal component analysis. The sensitivity of each to motion and other artifacts will be established by in in vivo comparisons and by computer simulations. From these studies, we anticipate being able to improve strategies for the use and interpretation of functional MRI in human studies of function and cognition.