Rapid calculation of static magnetic field perturbation generated by magnetized objects in arbitrary orientations

Area of Science:

• Medical Imaging
• Computational Physics
• Biophysics

Background:

• Static magnetic field (B₀) inhomogeneity calculations traditionally assume unidirectional fields.
• Accurate B₀ field mapping is crucial for Magnetic Resonance Imaging (MRI) quality, especially with implants or complex geometries.

Purpose of the Study:

• To develop and implement a computational method for calculating static magnetic field vectors from arbitrary distributions of voxelated magnetization.
• To extend existing B₀ calculation methods to handle arbitrary orientations of magnetization and magnetic fields.

Main Methods:

• Extended Fourier-domain convolution with k-space-discretized (KD) dipolar field and generalized susceptibility voxel convolution (gSVC) methods.
• Tested methods on analytical ellipsoid and tilted human head models.
• Validated against experimentally measured B₀ fields from a stainless-steel implant in a clinical 3T MRI scanner.

Main Results:

• Both KD and gSVC methods accurately calculated B₀ fields in magnetized ellipsoids across orientations.
• gSVC achieved comparable accuracy to KD but with generally shorter computation times and smaller grid requirements.
• gSVC-calculated fields closely matched experimental measurements for an implant, accounting for applied field variations.

Conclusions:

• The developed computational method offers a reliable and efficient tool for calculating B₀ perturbations.
• Applicable to diverse scenarios including inhomogeneous fields, anisotropic susceptibility, and rotated coordinate systems.
• Facilitates improved B₀ field prediction in complex MRI environments.