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

描述(申请人提供)：内侧颞叶(MTL)是一个重要的大脑区域，辅助情节记忆和学习功能。MTL包括海马结构，由组织学上和功能上不同的亚区组成，以及海马区外皮质。到目前为止，已经使用3特斯拉的高分辨率核磁共振研究了特定于子场的记忆功能。然而，7台特斯拉磁共振扫描仪能够获得超高分辨率的磁共振图像，潜在地可以更精细地解析功能激活 在诸如CA2和CA3这样的较小子场内的水平，同时为定位子场提供具有优越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对在更高的场强下获取具有可接受图像质量的功能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 mm~3的超高分辨率BOLD功能磁共振成像。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信噪比改善技术，以满足MTL中预先指定的信号质量指标。然后，我们将在一个实验中演示超高分辨率功能磁共振成像的实用性，该实验旨在消除CA3和DG亚区的BOLD功能磁共振激活。在7T Structure MRI中，将以地面真实组织学标记为参考来标记子场。实验范式将操作模式分离和基于模式完成的记忆过程，这已被证明在某些条件下在啮齿动物中不同地激活CA3和DG亚区，但在人类中尚未显示出类似的效果。如果成功，该项目将启用测试 关于健康大脑中人类情节记忆功能的复杂的MTL分区特定假说。此外，它还可以提供病理对情景记忆系统的影响的细粒度了解，因为MTL亚区的参与通常在许多神经疾病中显示出地形图特异性，包括阿尔茨海默病。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，以更好地表征正常功能以及病理对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.