Seeking optimal magnetic core shapes for strong gradient generation in Dipole Field Navigation

Dipole Field Navigation (DFN) has been proposed previously as a promising remote magnetic actuation method for the navigation of microscale agents in vascular networks for the targeted delivery of therapeutics. This method exploits the strong magnetic field of a magnetic resonance imaging scanner to bring the agents at saturation magnetization, and relies on the proper positioning of ferromagnetic cores around the patient in the scanner to induce strong magnetic gradients for navigation. It is currently the only method providing both the high field and high gradient strengths required for the navigation of microparticles at the human scale. Because of the simpler magnetic models of this shape, previous works on DFN considered only spherical ferromagnetic cores. This work investigates different core shapes and shows that the sphere can be outperformed for deep tissue interventions. The gradients around different shapes, calculated by finite element modeling, are compared in the context of typical DFN conditions. Results show that, for the same amount of ferromagnetic material, the hemisphere and the disc generate significantly higher gradients (>50% gains) in deep tissues. Using those shapes instead of spheres would therefore improve the performances of DFN for targeting deep regions in the body.