Bias-Field Rotation Encoding: Toward a Large-Aperture Magnetic Particle Imaging System

Magnetic Particle Imaging (MPI) provides high sensitivity and quantitative imaging by detecting the nonlinear magnetization response of magnetic nanoparticles (MNPs). Conventional field-free region encoding suffers from gradient decay, which limits imaging ability in large-aperture systems. Building on offset-field and field-strength encoding strategies, as well as our earlier permanent-magnet rotation scheme, this work introduces a large-scale MPI system fully driven by bias coils. Four horizontal encoding coils enable electrically controlled bias-field rotation, while depth-encoding coils extend planar encoding to three dimensions. Numerical simulations demonstrate a spatial resolution of approximately 3 mm within a 232 mm aperture, confirming the feasibility of the proposed design for large-scale MPI applications.