Intravoxel B₀ inhomogeneity corrected reconstruction using a low-rank encoding operator.

Area of Science:

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

Background:

• Macroscopic intravoxel magnetic field (B0) inhomogeneity is a common artifact in gradient echo (GRE) MRI.
• These B0 variations can degrade image quality and lead to inaccurate quantitative measurements.
• Existing correction methods are often computationally intensive or limited in scope.

Purpose of the Study:

• To develop a general and efficient method for correcting macroscopic intravoxel B0 inhomogeneity in multi-echo GRE acquisitions.
• To enable accurate image reconstruction from data affected by B0 variations.

Main Methods:

• A signal encoding model incorporating 3D intravoxel B0 field variations for multi-echo GRE was derived.
• A low-rank approximation of the encoding operator was introduced, assuming piecewise linear B0 fields.
• The model was integrated into general inverse problem formulations, supporting multi-coil, undersampled, and regularized reconstructions.

Main Results:

• Experimental validation using multi-echo GRE data demonstrated effective reduction of B0 inhomogeneity artifacts.
• The proposed method achieved improved B0 estimation compared to standard Fourier reconstruction.
• The low-rank approximation facilitated computationally efficient and memory-sparing reconstruction.

Conclusions:

• The developed method effectively corrects intravoxel B0 inhomogeneity artifacts in GRE MRI.
• This technique is broadly applicable to various MRI applications, including functional MRI (fMRI), quantitative B0 mapping, and MR spectroscopic imaging.