Susceptibility tensor imaging (STI) of the brain

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging
• Biophysics

Background:

• Conventional quantitative susceptibility mapping (QSM) uses scalar values, which may not fully capture orientation-dependent magnetic properties of tissues.
• Brain white matter exhibits orientation dependence in magnetic susceptibility due to its ordered structure, particularly myelin.

Purpose of the Study:

• To introduce and review Susceptibility Tensor Imaging (STI), a novel MRI technique for quantitative determination of orientation-independent magnetic susceptibility parameters.
• To explore the physical principles, practical implementations, and applications of STI in brain research.

Main Methods:

• Modeling voxel magnetic susceptibility as a symmetric rank-2 tensor.
• Analyzing the dependence of gradient echo signal phase on tissue orientation relative to the main magnetic field.
• Determining magnetic susceptibility tensor elements, mean susceptibility, and susceptibility anisotropy.

Main Results:

• STI can determine orientation-independent magnetic susceptibility parameters, including mean susceptibility and anisotropy.
• It enables mapping of white matter fiber orientations and 3D pathway reconstruction, analogous to diffusion tensor imaging.
• Susceptibility anisotropy in white matter is primarily determined by myelin and is sensitive to contrast agents.

Conclusions:

• STI provides a consistent framework for interpreting orientation-dependent MRI phase and susceptibility signals across scales.
• The technique offers unique insights into white matter microstructure, with myelin as a key determinant of susceptibility anisotropy.
• STI holds significant potential for advancing brain research and neuroimaging applications.