A novel phantom with dia- and paramagnetic substructure for quantitative susceptibility mapping and relaxometry

Area of Science:

• Medical Imaging
• Biophysics
• Materials Science

Background:

• Quantitative susceptibility mapping (QSM) is crucial for analyzing magnetic properties in biological tissues.
• Accurate QSM relies on robust reconstruction algorithms capable of distinguishing between diamagnetic and paramagnetic contributions.
• Sub-voxel level separation of these properties remains a challenge for current QSM techniques.

Purpose of the Study:

• To present a novel phantom for the experimental evaluation of QSM reconstruction algorithms.
• To provide a tool for assessing algorithms that separate isotropic dia- and paramagnetic susceptibility at the sub-voxel level.
• To facilitate the development and validation of advanced QSM methods.

Main Methods:

• The phantom was constructed using calcium carbonate (diamagnetic) and tungsten carbide (paramagnetic) particles within a gelatin matrix, surrounded by agarose gel.
• Varying mass fractions and mixing ratios of susceptibility sources were employed.
• Gradient echo data were acquired at 1.5T, 3T, and 7T, with susceptibility maps calculated using the MEDI toolbox and relaxation rates (ΔR₂*) determined via exponential fitting.

Main Results:

• Relaxation rates and susceptibility values generally aligned with theoretical predictions for particles in the static dephasing regime.
• Deviations were observed for relaxation rates at higher field strengths and with high susceptibility values.
• Raw MRI data are provided as supplementary material for academic use.

Conclusions:

• A susceptibility phantom has been developed for the quantitative validation of QSM reconstruction algorithms.
• This phantom is suitable for assessing algorithms designed to separate isotropic dia- and paramagnetic substructure in QSM.
• The presented phantom will aid in the advancement of QSM techniques for improved accuracy and application.