Differential effect of age on hippocampal subfields assessed using a new high-resolution 3T MR sequence

Abstract

Recent advances in neuroimaging have highlighted the interest to differentiate hippocampal subfields for cognitive neurosciences and more notably in assessing the effects of normal and pathological aging. The main goal of the present study is to investigate the effects of normal aging onto the volume of the different hippocampal subfields. For this purpose, we developed a new magnetic resonance sequence together with reliable tracing guidelines to assess the volume of different subfields of the hippocampus using a 3 Tesla scanner, and estimated the validity of a simpler and less time-consuming method based on the widely-used automatic Voxel-Based Morphometry (VBM) technique. Three hippocampal regions of interest were delineated on the right and left hippocampi of 50 healthy subjects between 18 and 68 years old corresponding to the CA1, subiculum and other (including CA2-3-4 and Dentate Gyrus) subfields. A strong effect of age was found on the volume of the subiculum only, with a decrease paralleling that of the global gray matter volume, while CA1 and other subfields seemed relatively spared. Although less precise than the ROI-tracing technique, the VBM-based method appeared as a reliable alternative especially to distinguish CA1 and subiculum subfields. Our findings of a specific effect of age on the subiculum are consistent with the developmental hypothesis ("last-in first-out" theory). This contrasts with the predominant vulnerability of the CA1 subfield to Alzheimer's disease reported in several previous studies, suggesting that the assessment of hippocampal subfields may improve the discrimination between normal and pathological aging.

High-resolution <em>In Vivo</em> Manual Segmentation Protocol for Human Hippocampal Subfields Using 3T Magnetic Resonance Imaging

“…However, existing protocols exclude portions of the hippocampus 20,23,33,35 , apply only to fixed images 37 , or require ultra-high field scanners for image acquisition 35,37 . This manuscript offers a segmentation protocol that includes five major subdivisions (CA1, CA2/CA3, CA4/dentate gyrus, SR/SL/SM, and subiculum) of the hippocampus and spans the entire anterior-posterior length of the structure.…”

“…Although images taken at a high field strength are able to offer detailed insight into hippocampal subfields, high-field scanners are not yet common in clinical or research settings, so 7T and 9.4T protocols currently have limited applicability. Similar protocols have been developed for images collected on 3T and 4T scanners 11,20,21,23,24,25,28,33 . Many of these protocols are based on images with sub-1mm voxels voxel dimensions in the coronal plane, but have large slice thicknesses (0.8-3 mm) 11,20,21,23,25,28,33 or large inter-slice distances 20,28 , both of which result in a significant measurement bias in the estimation of volumes of the individual subfields.…”

“…Many of these protocols are based on images with sub-1mm voxels voxel dimensions in the coronal plane, but have large slice thicknesses (0.8-3 mm) 11,20,21,23,25,28,33 or large inter-slice distances 20,28 , both of which result in a significant measurement bias in the estimation of volumes of the individual subfields. Additionally, many of the existing 3T protocols exclude subfields in all or part of the hippocampal head or tail 20,23,25,33 or do not provide detailed segmentations of important substructures (i.e., combine the DG with CA2/CA3 or do not include the strata radiatum/lacunosum/moleculare of the CA) 11,20,21,23,24,25,28,33 . There is therefore a need in the field for a detailed description of a protocol that can reliably identify relevant subfields throughout the head, body, and tail of the hippocampus that is based on a scanner commonly available in clinical and research settings.…”

La neuro-imagerie au service de la maladie d’Alzheimer

“…Insuffisant à lui seul, cet indice améliore cependant le diagnostic lorsqu'il est combiné à d'autres marqueurs (tels que des tests neuropsychologiques et d'autres mesures volumiques notamment [11]). Des travaux récents suggèrent également qu'une exploration plus détaillée de cette structure, distinguant ses différentes sous-parties, pourrait également accroître la sensibilité de cette mesure [12][13][14] (Figure 1B). Les résultats obtenus par TEP-FDG sont très encourageants pour le diagnostic précoce de cette maladie.…”

Segmentation ciblée d’images IRM et maladie d’Alzheimer

“…Par ailleurs, des études afin de différencier les sous-parties de l'hippocampe ont été proposées, à partir d'acquisitions spéci-fiques à 3T [50,51], 4T [52], 4,7T [53]. Cependant, ces méthodes reposent sur de nombreuses limites géométriques, et la mesure des volumes est rendue problématique par la résolution qui reste limitée à ∼0,4-0,5 mm dans le plan sur des coupes de l'ordre de 2 mm (coupes coronales perpendiculaires au grand axe des Fig.…”