Design of Saddle-Shaped Coils for Field Free Point Scanning in Magnetic Particle Imaging

Magnetic particle imaging (MPI) is an emerging medical imaging modality for quantitatively visualizing the spatial distribution of superparamagnetic iron oxide nanoparticles (SPIONs). In MPI, the design of the scanning coil is a critical component. It enables the rapid movement of the field free point (FFP) through the field of view (FOV) for fast imaging. Both Helmholtz coils and saddle-shaped coils are capable of generating a uniform scanning magnetic field. However, the saddle-shaped coil design is preferred due to its greater compactness. In this paper, we introduce an enhanced saddle-shaped coil design to optimize performance parameters, such as the homogeneity and efficiency of coil, through finite element method (FEM) and experiments. In addition, we also provide the geometric parameters for finite element simulation modeling of saddle-shaped coils, along with the criteria for selecting these geometric parameters. The simulation results show the influence of the geometric parameters of the saddle-shaped coil on its performance. Based on FEM and the geometric parameter analysis, we develop an improved scanning coil. The measurement results show that the saddle-shaped coil allows good homogeneity of 98.2%. In addition, 1D phantom imaging experiments are performed, which indicates a spatial resolution of 1.5 mm along the y-axis in the narrowband MPI scanner.