Iterative static field map estimation for off-resonance correction in non-Cartesian susceptibility weighted imaging

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Medical Physics
• Image Processing

Background:

• Patient-induced magnetic field inhomogeneities cause artifacts in susceptibility-weighted imaging (SWI).
• Conventional correction methods necessitate additional magnetic field map acquisitions, increasing scan time and complexity.
• Susceptibility-weighted imaging (SWI) is sensitive to magnetic field distortions, impacting image quality.

Purpose of the Study:

• To develop and validate a method for estimating static magnetic field maps directly from SWI data.
• To eliminate the need for separate magnetic field map acquisitions in SWI.
• To improve the accuracy and robustness of artifact correction in SWI.

Main Methods:

• Approximation of the static magnetic field map from a single echo acquisition in SWI.
• Utilizing long echo times (TE > 20 ms at 3T) to minimize non-linear field effects.
• Combining and unfolding multi-channel phase maps using advanced algorithms.
• Assessing the method with in vivo human brain data acquired using SPARKLING readouts.

Main Results:

• The proposed method generated 3D field maps with 0.6 mm isotropic resolution.
• Off-resonance corrections were comparable to external field map methods, with improvements in 2 out of 4 subjects.
• The new method showed robustness against volume mismatches and other error sources, unlike reference methods.

Conclusions:

• A novel static magnetic field map estimation method leverages long echo time acquisitions in SWI.
• The proposed technique outperforms traditional external field map methods in artifact correction.
• This approach offers a more robust and efficient solution for SWI artifact reduction.