Susceptibility tensor imaging

TLDR

Heterogeneity of magnetic susceptibility in brain tissues generates contrast between gray and white matter in gradient‑echo MR phase images. The study reports extensive anisotropic magnetic susceptibility in CNS white matter and introduces a susceptibility tensor imaging technique to quantify it. The technique measures resonance frequency offsets at multiple orientations relative to the main field, constructs an apparent susceptibility tensor, and decomposes it into three eigenvalues and eigenvectors independent of coordinate system. Principal susceptibilities provide strong gray‑white contrast, while eigenvectors reveal orientation of an underlying magnetic network that may reflect white‑matter fiber direction. Magn Reson Med 63:1471–1477, 2010; © 2010 Wiley‑Liss, Inc.

Abstract

Abstract Heterogeneity of magnetic susceptibility within brain tissues creates unique contrast between gray and white matter in magnetic resonance phase images acquired by gradient echo sequences. Detailed understanding of this contrast may provide meaningful diagnostic information. In this communication, we report an observation of extensive anisotropic magnetic susceptibility in the white matter of the central nervous system. Furthermore, we describe a susceptibility tensor imaging technique to measure and quantify this phenomenon. This technique relies on the measurement of resonance frequency offset at different orientations with respect to the main magnetic field. We propose to characterize this orientation variation using an apparent susceptibility tensor. The susceptibility tensor can be decomposed into three eigenvalues (principal susceptibilities) and associated eigenvectors that are coordinate‐system independent. We show that the principal susceptibilities offer strong contrast between gray and white matter, whereas the eigenvectors provide orientation information of an underlying magnetic network. We believe that this network may further offer information of white matter fiber orientation. Magn Reson Med 63:1471–1477, 2010. © 2010 Wiley‐Liss, Inc.