Quantifying MRI frequency shifts due to structures with anisotropic magnetic susceptibility using pyrolytic graphite sheet

Cronin, Matthew; Bowtell, Richard W.

Abstract

Magnetic susceptibility is an important source of contrast in magnetic resonance imaging (MRI), with spatial variations in the susceptibility of tissue affecting both the magnitude and phase of the measured signals. This contrast has generally been interpreted by assuming that tissues have isotropic magnetic susceptibility, but recent work has shown that the anisotropic magnetic susceptibility of ordered biological tissues, such as myelinated nerves and cardiac muscle fibers, gives rise to unexpected image contrast. This behavior occurs because the pattern of field variation generated by microstructural elements formed from material of anisotropic susceptibility can be very different from that predicted by modelling the effects in terms of isotropic susceptibility. In MR images of tissue, such elements are manifested at a sub-voxel length-scale, so the patterns of field variation that they generate cannot be directly visualized. Here, we used pyrolytic graphite sheet which has a large magnetic susceptibility anisotropy to form structures of known geometry with sizes large enough that the pattern of field variation could be mapped directly using MRI. This allowed direct validation of theoretical expressions describing the pattern of field variation from anisotropic structures with biologically relevant shapes (slabs, spherical shells and cylindrical shells).

Citation

Cronin, M., & Bowtell, R. W. (2018). Quantifying MRI frequency shifts due to structures with anisotropic magnetic susceptibility using pyrolytic graphite sheet. Scientific Reports, 8, Article 6259. https://doi.org/10.1038/s41598-018-24650-2

• Journal Article Type: Article
• Acceptance Date: Mar 26, 2018
• Publication Date: Apr 19, 2018
• Deposit Date: Apr 26, 2018
• Publicly Available Date: Apr 26, 2018
• Journal: Scientific Reports
• Electronic ISSN: 2045-2322
• Publisher: Nature Publishing Group
• Peer Reviewed: Peer Reviewed
• Volume: 8
• Article Number: 6259
• DOI: https://doi.org/10.1038/s41598-018-24650-2
• Public URL: https://nottingham-repository.worktribe.com/output/926794
• Publisher URL: https://www.nature.com/articles/s41598-018-24650-2
• Contract Date: Apr 26, 2018