Ultra-high resolution BOLD fMRI of medial temporal lobe at 7 Tesla

描述（由申请人提供）：内侧颞叶（MTL）是一个重要的大脑区域，有助于情景记忆和学习功能。MTL包含由组织学和功能上不同的子区域组成的海马结构和海马外皮质。到目前为止，已经使用3特斯拉的高分辨率MRI研究了子场特异性记忆功能。然而，7特斯拉MR扫描仪能够采集超高分辨率的MR图像，可以在更精细的分辨率下潜在地解决功能激活问题。 在诸如CA 2和CA 3之类的较小子场中的水平，并且同时提供具有用于定位子场的上级对比度特性的结构图像。然而，更小的体素和更大的磁场不均匀性对在更高的场强下采集具有可接受的图像质量的功能MRI数据提出了挑战，特别是在MTL中。在这个试点项目中，我们建议开发和优化MR采集序列，以获得分辨率为1x1x1 mm3的超高分辨率BOLD fMRI。我们将结合图像采集和后处理方法实施最先进的失真校正和SNR改善技术，以满足MTL中预先指定的信号质量指标。 然后，我们将在一个旨在分离CA3和DG子场中BOLD fMRI激活的实验中证明超高分辨率fMRI的实用性。将使用真实组织学标记作为参考，在7T结构MRI中标记子场。实验范式将操作模式分离和模式完成为基础的记忆过程，已被证明差异激活CA3和DG子字段在啮齿动物在某些条件下，但类似的效果还没有显示在人类。 如果成功，该项目将使测试 关于健康大脑中人类情景记忆功能的复杂的MTL亚区域特异性假设。此外，它可以提供对情节记忆系统的病理学影响的粒度理解，因为MTL亚区的参与通常在许多神经障碍（包括阿尔茨海默病）中显示出拓扑特异性。最后，这项工作将为未来基于成像的研究提供一个全面的图像采集和分析框架，以更好地表征规范功能以及病理对MTL支持的认知过程的影响。

DESCRIPTION (provided by applicant): The medial temporal lobe (MTL) is an important brain region that subserves functions of episodic memory and learning. MTL contains the hippocampal formation, composed of histologically and functionally distinct sub- fields, and extra-hippocampal cortices. Subfield-specific memory functions have so far been investigated using high-resolution MRI at 3 Tesla. However, 7 Tesla MR scanners are capable of acquiring ultra-high resolution MR images that can potentially resolve functional activation at an even finer level within smaller subfields such as CA2 and CA3, and at the same time provide structural images with superior contrast properties for localiz- ing subfields. However, smaller voxels and greater magnetic field inhomogeneity pose challenges to acquiring functional MRI data with acceptable image quality at higher field strengths, particularly in the MTL. In this pilot project,we propose to develop and optimize MR acquisition sequences to obtain ultra-high resolution BOLD fMRI at a resolution of 1x1x1 mm3. We will implement state-of-the-art distortion-correction and SNR improve- ment techniques using a combination of image acquisition and post-processing methods to satisfy pre- specified signal-quality metrics in the MTL. We will then demonstrate the utility of ultra-high resolution fMRI in an experiment designed to dissoci- ate BOLD fMRI activation in CA3 and DG subfields. Subfields will be labeled in 7T structural MRI using ground truth histological labeling as reference. The experimental paradigm will operationalize pattern separation and pattern completion-based memory processes which have been shown to differentially activate CA3 and DG subfields under certain conditions in rodents, but similar effects have not been shown in humans. If successful, this project will enable testing of complex, MTL subregion-specific hypotheses regarding human episodic memory function in healthy brain. Additionally, it can provide a granular understanding of ef- fects of pathology on the episodic memory system, as involvement of MTL subregions often show a topo- graphic specificity in many neurological disorders, including Alzheimer's Disease. Finally, this work will provide a comprehensive image acquisition and analysis framework for future imaging-based investigations to more finely characterize normative function as well as the effects of pathology on MTL-supported cognitive proc- esses.