Source-separated susceptibility tensor MRI reveals paramagnetic and diamagnetic anisotropy in a postmortem chimpanzee brain

Magnetic susceptibility in brain white matter is anisotropic because of the ordered arrangement of myelin lipids, whereas paramagnetic iron is generally not considered a source of susceptibility anisotropy. Whether spatially organized paramagnetic sources also contribute to tissue-level susceptibility anisotropy remains unclear. Here we analyze multi-orientation gradient-echo MRI and diffusion MRI data from a paraformaldehyde-fixed postmortem adult male western chimpanzee (Pan troglodytes verus) brain and use DECOMPOSE-QSM to separate paramagnetic and diamagnetic susceptibility components before tensor reconstruction.

The diamagnetic component shows the expected anisotropy in white matter and aligns with major diffusion-based fiber orientations. The paramagnetic component also shows coherent anisotropy, most prominently in deep gray matter and in parts of white matter. Numerical modeling further supports that an ordered spatial arrangement of otherwise isotropic paramagnetic sources can produce orientation-dependent susceptibility.

These results suggest that source-separated susceptibility tensor imaging provides complementary information about tissue-specific susceptibility organization beyond conventional susceptibility tensor imaging. This work was supported in part by the Alzheimer’s Drug Discovery Foundation through grant GC-201810-2017383 and by the EU through grant H2020-MSCA-ITN-2018 (“INSPiRE-MED”). Research reported in this publication was in part supported by the National Institutes of Health under Award Numbers R01AG070826 and R01MH127104.

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We thank the Ministère de l’Enseignement Supérieur et de la Recherche Scientifique and the Ministère des Eaux et Fôrets in Côte d’Ivoire, and the Office Ivoirien des Parcs et Réserves for permitting the study. We are grateful to the Centre Suisse de Recherches Scientifiques en Côte d’Ivoire and the staff members of the Taï Chimpanzee Project for their support and to Angela D.

Friederici, Nikolaus Weiskopf and other Evolution of Brain Connectivity (EBC) project organizers for kindly sharing the brain specimen. Present address: Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA Department of Electrical Engineering and Computer Sciences, University of California Berkeley, Berkeley, CA, USA Center for Advanced Imaging Innovation and Research, Department of Radiology, New York University Grossman School of Medicine, New York, NY, USA Nuclear Magnetic Resonance Methods & Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany Dimitrios G. Möller Translational Imaging in Neurology Basel, Department of Biomedical Engineering, Faculty of Medicine, University of Basel, Basel, Switzerland Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany Taï Chimpanzee Project, Centre Suisse de Recherches Scientifiques en Côte d’Ivoire, Abidjan, Côte d’Ivoire Jenny E.

Jaffe, Tobias Gräßle, Zoro B. Goné Bi, Catherine Crockford & Roman Wittig Helmholtz Institute for One Health, Greifswald, Germany Robert Koch Institute, Epidemiology of Highly Pathogenic Microorganisms, Berlin, Germany Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany Paul Flechsig Institute – Centre of Neuropathology and Brain Research, Leipzig University, Leipzig, Germany UFR Biosciences, Université Félix Houphouët-Boigny, Abidjan, Côte d’Ivoire Institute of Cognitive Sciences, CNRS UMR5229 University of Lyon, Bron, France Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, USA The authors declare no competing interests. Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.