Susceptibility source separation from gradient echo data using magnitude decay modeling.

Area of Science:

• Medical Imaging
• Neuroimaging
• Biomarkers

Background:

• Quantitative susceptibility mapping (QSM) is crucial for neuroimaging.
• Separating magnetic sources in QSM aids in understanding tissue properties.
• Current methods often require multiple MRI sequences.

Purpose of the Study:

• To demonstrate the feasibility of separating magnetic sources in QSM using only gradient echo (GRE) MRI magnitude decay rates.
• To compare a novel method using magnitude decay rates with a prior method using R2*.
• To evaluate the potential of this new method as a biomarker for myelin changes in multiple sclerosis (MS).

Main Methods:

• Developed a magnetic susceptibility source separation method incorporating magnitude decay rates ($$) from GRE MRI.
• Compared the novel $$-based method with a prior $$-based method in 17 multiple sclerosis (MS) patients.
• Correlated susceptibility values from $$-based separation with longitudinal myelin water fraction (MWF) changes in 44 enhancing MS lesions.

Main Results:

• High agreement between $$-based and $$-based susceptibility separation methods (r=0.96, slope=0.99) in vivo.
• Significant positive association found between $$ increase and MWF increase in enhancing MS lesions (β = -0.144, p=0.0008).
• Good agreement between the two methods in enhancing lesions (r=0.79, slope=0.95).

Conclusions:

• Magnetic source separation in QSM is feasible using only GRE complex data by combining magnitude decay rate modeling and phase-based QSM.
• $$ change shows promise as a biomarker for myelin recovery or damage in acute MS lesions.
• This approach simplifies QSM by potentially reducing the need for additional MRI sequences.