Novel insights into hippocampal perfusion using high-resolution, multi-modal 7T MRI

Abstract

We present a comprehensive study on the non-invasive measurement of hippocampal perfusion. Using high-resolution 7 Tesla arterial spin labelling data, we generated robust perfusion maps and observed significant variations in perfusion among hippocampal subfields, with CA1 exhibiting the lowest perfusion levels. Notably, these perfusion differences were robust and detectable even within five minutes and just fifty perfusion-weighted images per subject. To understand the underlying factors, we examined the influence of image quality metrics, various tissue microstructure and morphometry properties, macrovasculature and cytoarchitecture. We observed higher perfusion in regions located closer to arteries, demonstrating the influence of vascular proximity on hippocampal perfusion. Moreover,ex vivocytoarchitectonic features based on neuronal density differences appeared to correlate stronger with hippocampal perfusion than morphometric measures like gray matter thickness. These findings emphasize the interplay between microvasculature, macrovasculature, and metabolic demand in shaping hippocampal perfusion. Our study expands the current understanding of hippocampal physiology and its relevance to neurological disorders. By providingin vivoevidence of perfusion differences between hippocampal subfields, our findings have implications for diagnosis and potential therapeutic interventions. In conclusion, our study provides a valuable resource for extensively characterising hippocampal perfusion.

Vessel distance mapping: a novel methodology for assessing vascular‐induced cognitive resilience

“…Inspired by previous studies assessing vasculature with respect to its surrounding anatomy by using distances ( Haast et al, 2021 ;Bause et al, 2020 ;Huck et al, 2019 ;Bernier et al, 2018 ), we termed our approach as Vessel Distance Mapping (VDM) ( Mattern et al, ESMRMB 2020 ;Mattern, ESMRMB 2021, ISMRM 2021. Based on vessel segmentation, VDM computes for each voxel the distance to the closest vessel using the Euclidian distance transform.…”

“…Future investigations are required to understand the complementary nature of both approaches comprehensively to enable more precise predictions and, in combination with deep learning-based multilabel vessel segmentation, a fully automatic hippocampal vascularization assessment. Further, given that VDM allows for the evaluation of the vessel structure from high resolution ToF angiography, this could be combined with ASL-based perfusion data to study the structure and function of the hippocampal vascularization at the mesoscopic scale ( Haast et al, 2021 ). Additionally, VDM uses the distance between a voxel and a vessel to estimate the vessel's relevance in the blood supply, without measuring vessel territories directly.…”

HippoMaps: Multiscale cartography of the human hippocampal formation

“…This has begun a new wave of high-sensitivity hippocampally-focused studies in topics including the mapping of histology features (J. DeKraker et al, 2020; Paquola, Benkarim, et al, 2020), blood perfusion (Haast et al ., 2023; Ngo et al ., 2023), biophysically-constrained diffusion (Karat et al ., 2023), hippocampal sclerosis (Ripart et al ., 2023), neurodevelopmental trajectories (Hanson et al ., 2023), functional connectivity (Cabalo et al ., 2023; Lariviere et al ., 2023; Xie et al ., 2023), visual receptive field mapping (Leferink et al ., 2023), and cross-species comparison (Eichert et al ., 2023). With the increasing aggregation of hippocampal features in a common reference space, it is now possible to devise repositories that allow for a broad contextualization of hippocampal findings.…”

“…Similar to neocortical surface extraction and registration procedures (Boucher et al, 2009;Dale et al, 1999;Fischl, Sereno, Tootell, et al, 1999;Kim et al, 2005;Lyttelton et al, 2007;MacDonald et al, 2000), this allows for topology-informed inter-subject registration to a standardized unfolded space (Jordan DeKraker et al, 2023). This has begun a new wave of high-sensitivity hippocampally-focused studies in topics including the mapping of histology features , blood perfusion (Haast et al, 2023;Ngo et al, 2023), biophysically-constrained diffusion (Karat et al, 2023), hippocampal sclerosis (Ripart et al, 2023), neurodevelopmental trajectories (Hanson et al, 2023), functional connectivity (Cabalo et al, 2023;Lariviere et al, 2023;Xie et al, 2023), visual receptive field mapping (Leferink et al, 2023), and crossspecies comparison (Eichert et al, 2023). With the increasing aggregation of hippocampal features in a common reference space, it is now possible to devise repositories that allow for a broad contextualization of hippocampal findings.…”

Characterizing BOLD activation patterns in the human hippocampus with laminar fMRI

“…Recent advances in ultra-high field (UHF) fMRI made it possible to obtain structural 7 and physiological 1,8 information from the human hippocampus with sub-millimeter resolution. This high spatial resolution allows fMRI responses to be probed as a function of depth (also known as laminar fMRI).…”