A Diffeomorphic Vector Field Approach to Analyze the Thickness of the Hippocampus from 7T MRI

Alexis Guyot (1, 2) , Ana B Graciano Fouquier (1, 2) , Emilie Gerardin (1, 2) , Marie Chupin (1, 3) , Joan Glaunès (4) , Linda Marrakchi-Kacem (1, 5) , Johanne Germain (1) , Claire Boutet (1) , Claire Cury (6, 1) , Lucie Hertz-Pannier (7, 8, 9) , Alexandre Vignaud (7) , Stanley Durrleman (1, 2) , Thomas Henry (10) , Pierre-François van de Moortele (11) , Alain Trouvé (1, 12, 13) , Olivier Colliot (2, 1)

1 ICM - Institut du Cerveau = Paris Brain Institute
2 ARAMIS - Algorithms, models and methods for images and signals of the human brain = Algorithmes, modèles et méthodes pour les images et les signaux du cerveau humain [ICM Paris]
3 CATI - Centre d'Acquisition et de Traitement des Images [Paris] = CATI Multicenter Neuroimaging Platform
4 MAP5 - UMR 8145 - Mathématiques Appliquées Paris 5
5 ISBST - Institut Supérieur de Biotechnologie de Sidi Thabet
6 Empenn - Neuroimagerie: méthodes et applications
7 NEUROSPIN - Service NEUROSPIN
8 INSERM - Institut National de la Santé et de la Recherche Médicale
9 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
10 University of Minnesota Medical School
11 CMRR - Center for Magnetic Resonance Research [Minneapolis]
12 CMLA - Centre de Mathématiques et de Leurs Applications
13 CB - CB - Centre Borelli - UMR 9010

OBJECTIVE. 7-Tesla MRI of the hippocampus enhances the visualization of its internal substructures. Among these substructures, the cornu Ammonis and subiculum form a contiguous folded ribbon of gray matter. Here, we propose a method to analyze local thickness measurements of this ribbon. METHODS. We introduce an original approach based upon the estimation of a diffeomorphic vector field that traverses the ribbon. The method is designed to handle specificities of the hippocampus and corresponding 7-Tesla acquisitions: highly convoluted surface, non closed ribbon, incompletely defined inner/outer boundaries, anisotropic acquisitions. We furthermore propose to conduct group comparisons using a population template built from the central surfaces of individual subjects. RESULTS. We first assessed the robustness of our approach to anisotropy, as well as to inter-rater variability, on a post-mortem scan and on in vivo acquisitions respectively. We then conducted a group study on a dataset of in vivo MRI from temporal lobe epilepsy (TLE) patients and healthy controls. The method detected local thinning patterns in patients, predominantly ipsilaterally to the seizure focus, which is consistent with medical knowledge. CONCLUSION. This new technique allows measuring the thickness of the hippocampus from 7-Tesla MRI. It shows good robustness with respect to anisotropy and inter-rater variability and has the potential to detect local atrophy in patients. SIGNIFICANCE. As 7-Tesla MRI is increasingly available, this new method may become a useful tool to study local alterations of the hippocampus in brain disorders. It is made freely available to the community (code: https://github.com/aramis-lab/hiplay7-thickness, postmortem segmentation: https://doi.org/10.5281/zenodo.3533264).

Mots clés: Ultra-high-field; Hippocampus; Morphometry; Diffeomorphism; Magnetic Resonance Imaging; Thickness; 7-Tesla

Domaines: Imagerie médicale; Neurosciences; Traitement des images [eess.IV]

Alexis Guyot, Ana B Graciano Fouquier, Emilie Gerardin, Marie Chupin, Joan Glaunès, et al.. A Diffeomorphic Vector Field Approach to Analyze the Thickness of the Hippocampus from 7T MRI. IEEE Transactions on Biomedical Engineering, 2021, 68 (2), pp.393-403. ⟨10.1109/TBME.2020.2999941⟩. ⟨hal-02359660v2⟩