Imaging Brain Activation with Steady-State Free Precession MRI

描述(申请人提供)：功能磁共振成像(FMRI)通过提供非侵入性工具来监测与大脑激活相关的血氧或组织灌注的变化，从而使神经科学发生了革命性的变化。最常见的方法是血氧依赖(BOLD)成像。不幸的是，提供BOLD氧气敏感性的MRI采集参数也会对图像伪影、信号丢失和空间失真产生敏感性。这项提议的目的是开发不受这些限制的BOLD的替代方案。这项建议中描述的新方法是基于快速、短时间、完全重新聚焦的成像采集技术中依赖氧的信号变化，称为稳态自由进动，或SSFP。这些方法利用了由于氧气变化而引起的稳态信号的变化。一旦建立了这种依赖于氧的稳态对比度，就可以用任何图像编码方法来捕捉它，可以选择这种方法来提高效率、分辨率和对伪影的免疫力。其结果是在大脑的任何区域实现高分辨率、各向同性，没有信号丢失或空间失真。这将是神经科学家可用来研究大脑激活的工具的重要补充。具体地说，该项目旨在开发两种不同的方法来利用功能磁共振的SSFP响应。第一种是利用SSFP过渡带的频率灵敏度来检测血氧变化引起的绝对频移。第二种是利用氧相关的表观T2变化到稳态磁化强度。然后，这些技术将被评估，并在视觉系统的良好特征研究中与传统的BOLD进行比较。

DESCRIPTION (provided by applicant): Functional magnetic resonance imaging (fMRI) has revolutionized the neurosciences by providing noninvasive tools for monitoring changes in blood oxygenation or tissue perfusion associated with brain activation. The most common approach is blood oxygenation dependent (BOLD) imaging. Unfortunately, the MRI acquisition parameters that provide the oxygen sensitivity in BOLD also produce sensitivity to image artifacts, signal dropouts, and spatial distortion. The aim of this proposal is to develop alternatives to BOLD without these limitations. The new methods described in this proposal are based on oxygen-dependent signal changes in rapid, short TR, fully refocused imaging acquisition techniques, known as steady-state free precession, or SSFP. These approaches exploit the changes in the steady-state signal due to oxygenation changes. Once this steady-state oxygenation dependent contrast has been established, it can be captured with any image encoding method, which can be chosen for efficiency, resolution, and immunity to artifacts. The result is high-resolution, isotropic in any area of the brain, without signal dropouts or spatial distortion. This will be an important addition to the tools available to neuroscientists for studying brain activation. Specifically, this project aims to develop two different approaches for exploiting the SSFP response for fMRI. The first uses the frequency sensitivity of the SSFP transition band to detect absolute frequency shifts from blood oxygenation changes. The second exploits oxygen-dependent apparent T2 changes to the steady state magnetization. These techniques will then be evaluated and compared with conventional BOLD in well characterized studies of the visual system.