Hippocampal subfields at ultra high field MRI: An overview of segmentation and measurement methods

Abstract

The hippocampus is one of the most interesting and studied brain regions because of its involvement in memory functions and its vulnerability in pathological conditions, such as neurodegenerative processes. In the recent years, the increasing availability of Magnetic Resonance Imaging (MRI) scanners that operate at ultra-high field (UHF), that is, with static magnetic field strength ≥7T, has opened new research perspectives. Compared to conventional high-field scanners, these systems can provide new contrasts, increased signal-to-noise ratio and higher spatial resolution, thus they may improve the visualization of very small structures of the brain, such as the hippocampal subfields. Studying the morphometry of the hippocampus is crucial in neuroimaging research because changes in volume and thickness of hippocampal subregions may be relevant in the early assessment of pathological cognitive decline and Alzheimer's Disease (AD). The present review provides an overview of the manual, semi-automated and fully automated methods that allow the assessment of hippocampal subfield morphometry at UHF MRI, focusing on the different hippocampal segmentation produced. © 2017 Wiley Periodicals, Inc.

Keywords: hippocampal subfields; morphometry; quantification; segmentation; ultra-high field MRI.

Figure 1

In vivo coronal T₂*‐weighted images at 7T of hippocampal head (A,B) and body (C,D). Very small hippocampal structures are visible, such as cornu ammonis (CA1‐4), dentate gyrus (DG) and subiculum (SUB). In the cornu ammonis, especially in CA1, it is possible to distinguish between the stratum pyramidale (SP) and the composite of the strata radiatum, lacunosum and moleculare and the vestigial hippocampal sulcus (SRLM). A = alveus, ERC = entorhinal cortex, PHG = para‐hippocampal gyrus.