Effects of white matter microstructure on phase and susceptibility maps

Area of Science:

• Neuroimaging
• Biophysics
• Magnetic Resonance Imaging (MRI)

Background:

• Quantitative susceptibility mapping (QSM) and susceptibility tensor imaging (STI) are advanced MRI techniques used to study tissue magnetic properties.
• White matter (WM) microstructure influences magnetic field variations, potentially affecting the accuracy of QSM and STI.

Purpose of the Study:

• To investigate the impact of white matter (WM) microstructure on quantitative susceptibility mapping (QSM) and susceptibility tensor imaging (STI).
• To characterize frequency variations in WM tissue not attributable to bulk magnetic susceptibility.

Main Methods:

• Frequency offsets in WM tissue samples were analyzed to distinguish microstructure effects from bulk susceptibility.
• QSM and STI were applied to simulated frequency maps derived from a WM model based on MRI data.
• Magnitudes of frequency contributions from anisotropy and microstructure were quantified.

Main Results:

• Microstructure-related frequency contributions were found to be substantially larger than bulk anisotropic susceptibility effects.
• In QSM, microstructure led to artificial heterogeneity within white matter.
• STI processing showed significant overestimation of susceptibility anisotropy due to microstructure.

Conclusions:

• Microstructure-dependent phase offsets in white matter introduce artifacts into susceptibility maps.
• Addressing these microstructure-related frequency contributions is crucial for developing robust QSM and STI techniques.