Quantitation of the BOLD Effect in Functional MRI

功能 MRI 中 BOLD 效应的定量

• 批准号: 7269293
• 负责人: Peter CM Van Zijl
• 金额: $ 37.37万
• 依托单位: JOHNS HOPKINS UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-04-01 至 2009-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7269293
• 关键词: Blood; Blood Volume; Brain; Cerebrum; Complex; Data; Erythrocytes; Functional Magnetic Resonance Imaging; Goals; Grant; Magnetic Resonance Imaging; Measures; Metabolism; Oxygen; Physiological; Physiology; Property; Rate; Relaxation; Secondary to; Signal Transduction; Stimulus; Tissues; Veins; base; blood oxygenation level dependent response; channel blockers; hemodynamics; in vivo; insight; magnetic field; research study; response; size; theories; water channel

DESCRIPTION (provided by applicant): The BOLD-fMRI approach has revolutionized assessment of brain function. This complex effect represents MRI signal changes that are consequential to a hemodynamic response secondary to activation. As the BOLD response reflects the changing oxygen extraction fraction, OEF, it allows some insight into basic brain physiology. However, such interpretations are confounded by multiple contributions to the effect. BOLD is sensitive not only to intravascular oxygenation changes, but also to extravascular effects of such changes around parenchyma and around veins draining from activated cortex. In addition, BOLD is influenced by alterations in voxel composition due to changes in cerebral blood volume (CBV). Contributions of these effects to the BOLD signal intensity changes depend on magnetic field strength, voxel size, type of MRI experiment (spin echo/gradient echo). Thus, there are many variables and few observable parameters. In the previous period we have developed a new fMRI approach that can add several essential observables, namely tissue fractions, CBV and the tissue relaxation rates. We also re-interpreted the BOLD post-stimulus undershoot in terms of continued oxygen metabolism and showed that, surprisingly, BOLD spin-echo signals can occur in draining veins. The ultimate goal of this proposal is to gain a complete quantitative understanding of the physiological, physical, and spatial aspects of the BOLD effect. In AIM 1 we propose experiments to confirm the proposed oxygen-metabolism based character of the BOLD post-stimulus undershoot and to develop strategies to use this undershoot for fMRI voxel selection. In AIM 2 we propose experiments that can distinguish intravascular, extravascular, macrovascular, and microvascular BOLD components. This data will be used to evaluate existing extravascular BOLD theories. In AIM 3 we measure the blood transverse relaxation rates for blood in which the transport properties of erythrocyte water channels are impaired by an aquaporin channel blocker. This will be combined with our previous data without blocker to evaluate the effect of exchange versus magnetic field gradients on the intravascular BOLD effect. Based on our blood data acquired in the previous grant period and our in vivo data proposed to be acquired here, we will derive a quantitative description for the BOLD effect that has only physiological and physical parameters. This formalism should allow description of the BOLD effect for all physiological perturbations.

描述（由申请人提供）：BOLD-fMRI方法彻底改变了大脑功能的评估。这种复杂的效应代表了MRI信号的变化，这些变化是由激活引起的血流动力学反应引起的。由于BOLD响应反映了氧提取分数（OEF）的变化，因此可以对基本的大脑生理学进行一些深入了解。然而，这种解释被多种因素所混淆。BOLD不仅对血管内氧合变化敏感，而且对实质周围和从激活皮质引流的静脉周围的这种变化的血管外效应敏感。此外，BOLD还受脑血容量（CBV）变化引起的体素组成变化的影响。这些效应对BOLD信号强度变化的影响取决于磁场强度、体素大小、MRI实验类型（自旋回波/梯度回波）。因此，存在许多变量和很少的可观察参数。在前一阶段，我们已经开发了一种新的功能磁共振成像方法，可以添加几个基本的观测值，即组织分数，CBV和组织弛豫率。我们还重新解释了BOLD后刺激下冲在持续的氧代谢方面，并表明，令人惊讶的是，BOLD自旋回波信号可以发生在引流静脉。该提案的最终目标是获得对BOLD效应的生理、物理和空间方面的完整定量理解。在AIM 1中，我们提出了实验来证实所提出的氧代谢为基础的字符的BOLD刺激后的下冲，并制定策略，使用此下冲功能磁共振成像体素选择。在AIM 2中，我们提出了可以区分血管内、血管外、大血管和微血管BOLD成分的实验。这些数据将用于评估现有的血管外BOLD理论。在AIM 3中，我们测量了红细胞水通道的运输特性被水通道蛋白通道阻滞剂损害的血液的血液横向弛豫速率。这将与我们先前的无阻滞剂的数据相结合，以评价交换与磁场梯度对血管内BOLD效应的影响。基于我们在上一个资助期获得的血液数据和我们在此拟获得的体内数据，我们将推导出仅具有生理和物理参数的BOLD效应的定量描述。这种形式主义应该允许描述BOLD效应的所有生理扰动。