MagRing-MPI: design of electrically controlled FFL-MPI system based on a dynamic ring-shaped gradient array.

Objective: This study aims to propose and validate a novel electrically controlled field-free line (FFL) magnetic particle imaging (MPI) system to address several aspects of existing electronically rotated FFL-MPI designs, including limitations in gradient enhancement, structural complexity of the drive system, and coil coupling effects. Methods: We employ a dynamic ring-shaped magnetic-field-converging gradient array (dRMGA), consisting of multiple pairs of electromagnets symmetrically arranged along the radial and axial directions. This configuration ensures that the magnetic field direction of the generated FFL remains consistently perpendicular to both the gradient direction and the imaging plane. Tomographic imaging uses only one set of drive coils arranged orthogonally to the gradient coils. Three-dimensional FFL scanning is realized by dynamically modulating the current phase of the radial coil pairs in conjunction with differential current control of the axial coil pairs. In addition, we conduct electromagnetic and image reconstruction simulations to evaluate the FFL generation characteristics and reconstruction performance under magnetic configurations with different numbers of pole pairs. Results: Simulation results demonstrate that the proposed system can achieve efficient and stable FFL rotation and axial translation, supporting rapid 3D tomographic scanning. In addition, we systematically analyzed how different pole-pair configurations affect the quality of the generated FFL and the resulting image resolution. These findings offer concrete guidance on how pole-pair scaling influences gradient strength, field uniformity, and system complexity. Significance: The proposed MagRing-MPI system enhances magnetic field gradients and imaging quality, simplifies the drive-coil configuration to reduce system complexity, and minimizes electromagnetic coupling and feedthrough effects. These improvements provide a promising foundation for the development of scalable and high-performance MPI systems.