Functional imaging of hippocampal layers using VASO and BOLD on the Next Generation (NexGen) 7T Scanner

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Neuroscience

Background:

• Mesoscale fMRI faces challenges in subcortical regions due to low contrast-to-noise ratio (CNR), physiological noise, and complex vasculature.
• Venous biases are a significant concern, potentially affecting the accuracy of functional measurements.

Purpose of the Study:

• To optimize cerebral blood volume (CBV) VASO on a NexGen 7T scanner for layer-specific hippocampal investigations.
• To compare venous biases in VASO and BOLD (Blood-Oxygen-Level-Dependent) signals during an autobiographical memory task.

Main Methods:

• Optimized CBV VASO sequence timing on a NexGen 7T scanner.
• Acquired fMRI data during an autobiographical memory task using both VASO and BOLD sequences.
• Analyzed layer-specific activation patterns and venous biases within the hippocampus.

Main Results:

• VASO and BOLD activation patterns converged at the macroscale but showed layer-specific differences in the subiculum, indicating venous bias.
• Layer-specific differences in the subiculum are attributed to its unique two-sided venous drainage.
• Both VASO and BOLD detected sensitivity to short task blocks, revealing an anterior-posterior hippocampal distinction.

Conclusions:

• Optimized mesoscale fMRI enables high-accuracy mapping of hippocampal layer function.
• This advanced MR imaging technique allows precision mapping of subcortical gray matter.
• Provides deeper insights into neuropsychological conditions and early changes in Alzheimer's disease and mild cognitive impairment.