Effects of Duty Cycle on Magnetostimulation Thresholds in MPI

Abstract

Magnetic Particle Imaging (MPI) relies on time-varying magnetic fields to generate an image of the spatial distribution of superparamagnetic iron oxide nanoparticles. However, these oscillating magnetic field form electric field patterns within the body, which in turn can cause peripheral nerve stimulations (PNS), also known as magnetostimulation. To prevent potential safety hazards and to optimize the scanning parameters such as field-of-view (FOV) and scanning speed in MPI, the factors that affect drive field magnetostimulation limits need to be determined accurately. In this work, we investigate the effects of the duty cycle on magnetostimulation thresholds in MPI. We performed human subject experiments by using a highly homogenous solenoidal coil on the upper arm of six subjects. Six different duty cycles ranging between 5\% and 100\% were applied at 25 kHz. Accordingly, magnetostimulation limits first decrease and then increase with increasing duty cycle, reaching a maximum at 100\% duty cycle. Since high duty cycles would be the preferred operating mode for rapid imaging with MPI, these results have promising implications for future human-sized MPI systems.