Multiple sclerosis lesion geometry in quantitative susceptibility mapping (QSM) and phase imaging

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Medical Physics

Background:

• Multiple sclerosis (MS) lesions exhibit complex magnetic susceptibility distributions.
• Differentiating solid and shell-shaped susceptibility patterns is crucial for accurate lesion characterization in MS.
• Phase imaging in MRI can be ambiguous in representing these complex geometries.

Purpose of the Study:

• To compare the ability of quantitative susceptibility mapping (QSM) and phase imaging to depict solid versus shell spatial distributions of magnetic susceptibility.
• To evaluate the appearance of MS lesions on QSM and phase images.

Main Methods:

• Numerical simulations and experimental phantoms were used to generate MRI data for solid and shell susceptibility sources.
• Magnitude, phase, and QSM images were reconstructed from simulated and phantom data.
• MRI scans of 20 MS patients were reviewed to assess lesion appearance on phase and QSM images.

Main Results:

• QSM successfully reconstructed both solid and shell susceptibility geometries.
• Phase images displayed shell-like patterns for both solid and shell sources, hindering differentiation.
• In MS patients, QSM identified 83% of lesions as solid and 17% as shell, while phase imaging showed 30% solid and 70% shell.
• A significant portion of lesions appearing shell-like on phase were identified as solid on QSM.

Conclusions:

• QSM provides accurate differentiation of solid and shell magnetic susceptibility patterns in MS lesions.
• Phase imaging alone is insufficient to distinguish between solid and shell susceptibility distributions.
• QSM offers improved characterization of MS lesion microarchitecture compared to phase imaging.