An external reference to enable quantitative susceptibility mapping (QSM) in absolute terms: theoretical...

Area of Science:

• Medical Imaging
• Biophysics
• Magnetic Resonance Imaging

Background:

• Quantitative susceptibility mapping (QSM) is a semi-quantitative MRI technique.
• Current QSM methods lack a stable internal reference, hindering longitudinal and inter-subject comparisons.
• Absolute magnetic susceptibility quantification is crucial for advanced MRI applications.

Purpose of the Study:

• To propose and validate a novel phase-based approach for QSM using an external reference.
• To establish a theoretical framework linking phase measurements to absolute magnetic susceptibility.
• To enable accurate and reproducible QSM across different subjects and time points.

Main Methods:

• Developed a theoretical framework by modeling object geometry and analyzing induced magnetic field distortions.
• Validated the approach using a numerical head phantom and 3T MRI scans of phantoms and a healthy volunteer.
• Utilized accurate phase measurements to derive absolute mean magnetic susceptibility.

Main Results:

• Demonstrated excellent accuracy in numerical simulations.
• Achieved encouraging, though slightly underestimated, susceptibility values in MRI phantom measurements.
• Showed excellent correlation (r=0.98, p=0.004) between measured and theoretical susceptibility.
• Obtained an absolute mean susceptibility of 0.02 ppm relative to water in vivo.

Conclusions:

• The proposed phase-based method is feasible and provides a proof of concept for absolute QSM.
• This approach offers a valuable alternative reference solution for conventional QSM.
• Potential to facilitate the generation of absolute QSM maps for enhanced clinical and research applications.