Quantitation of the BOLD Effect in Functional MRI

功能 MRI 中 BOLD 效应的定量

• 批准号: 7100251
• 负责人: Peter CM Van Zijl
• 金额: $ 37.94万
• 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 2008-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7100251
• 关键词: acidity /alkalinity; bioimaging /biomedical imaging; blood volume; brain circulation; brain imaging /visualization /scanning; cerebrovascular imaging /visualization; clinical research; functional magnetic resonance imaging; hemoglobin; human subject; method development; oxygen tension; oxyhemoglobin

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方法彻底改变了对大脑功能的评估。这种复杂的效应代表了MRI信号的变化，这些变化是继发于激活的血液动力学反应的结果。由于大胆的反应反映了氧气提取分数的变化，OEF，它让我们对基本的大脑生理学有了一些了解。然而，这种解释因多方面的影响而变得混乱。BOLD不仅对血管内氧合变化敏感，而且对从激活皮质引流的实质和静脉周围的这种变化的血管外影响也很敏感。此外，由于脑血容量(CBV)的变化，体素组成的变化也会影响BOLD。这些效应对BOLD信号强度变化的贡献取决于磁场强度、体素大小、MRI实验的类型(自旋回波/梯度回波)。因此，变量较多，可观测参数较少。在前一阶段，我们开发了一种新的功能磁共振成像方法，该方法可以添加几个基本的观察参数，即组织分数、CBV和组织松驰率。我们还从持续氧气代谢的角度重新解释了刺激后大胆的不足，并表明，令人惊讶的是，大胆的自旋回波信号可以出现在引流的静脉中。这项提议的最终目标是对大胆效应的生理、物理和空间方面进行全面的量化理解。在目标1中，我们建议进行实验，以证实大胆的刺激后未达标基于氧代谢的特征，并开发利用该未达标进行功能磁共振体素选择的策略。在目标2中，我们提出了能够区分血管内、血管外、大血管和微血管BOLD成分的实验。这些数据将被用来评估现有的血管外大胆理论。在AIM 3中，我们测量了水通道阻滞剂损害红细胞水通道运输特性的血液的横向松弛速率。这将与我们之前没有阻滞剂的数据相结合，以评估交换与磁场梯度对血管内BOLD效应的影响。基于我们在前一次资助期间获得的血液数据和我们拟在这里获得的体内数据，我们将推导出只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对所有生理扰动的大胆影响进行描述。