Advances in High-Resolution Functional Mri of Squirrel Monkey Brain at 9.4t Mri

Abstract

High-resolution functional MRI (fMRI) has significantly advanced our understanding of brain networks, providing unique insights into neural dynamics at a laminar scale. This dissertation focuses on developing and optimizing high-resolution fMRI techniques for studying the squirrel monkey brain at 9.4T, including advancements in RF coil design and comparative evaluations of imaging sequences, as well as validating the functional relevance of resting-state functional connectivity (rsFC) through comparisons with optogenetic and tactile stimulation paradigms. Firstly, an optimized quadrature birdcage RF coil was specifically designed for imaging squirrel monkey brain at 9.4T with refinements in coil length and shielding, which improved signal-to-noise ratio (SNR) and temporal SNR (tSNR), crucial for capturing fine-scale neural activity. Secondly, Gradient-echo (GE) and spin-echo (SE) sequences were comparatively evaluated for their sensitivity to layer-specific blood oxygen level-dependent (BOLD) effects during tactile stimulation and resting state. Additionally, Anderson-Weiss mean field theory was employed to provide insights into vessel size distributions, further enhancing our understanding of the physiological mechanisms underlying BOLD effects across cortical layers. Finally, the neural underpinnings and functional relevance of rsFC were investigated by directly comparing rsFC networks derived from resting-state fMRI BOLD signals with activation patterns elicited by neuron-type-specific optogenetic stimulation of excitatory neurons in the S2 cortex and natural tactile stimulation of the fingers. These results suggest that rsFC can serve as a reliable tool for assessing functional brain organization and mapping intrinsic connectivity patterns. Overall, this dissertation advances the field of high-resolution functional MRI by optimizing RF coils associated with preclinical imaging at 9.4T, comparing imaging sequences, and validating the functional relevance of resting-state functional connectivity.