Comparison of different coil topologies for an MPI relaxometer

Magnetic Particle Imaging (MPI) has gained a variety of potential applications since its first introduction in 2005 [1]. It offers safe tracers with applications in angiography, stem cell tracking, and cancer imaging [2]. The response of superparamagnetic iron oxide (SPIO) nanoparticles strongly affects the quality of the MPI images, which is a unique and not-before-seen feature for a medical imaging system [3]. In theory, as the diameter of the nanoparticle increases, the resolution also increases [1-4]. In reality, however, larger nanoparticles start to lag behind the rapidly changing drive field [5-6]. This effect, called “relaxation”, causes the resolution and the signal-to-noise ratio (SNR) of the MPI images to degrade. Therefore, characterization of the nanoparticle response has an essential role in determining and ultimately improving the quality of the MPI systems. Previously, measurements of the point spread function and relaxation effects were performed using an MPI relaxometer with a gradiometer receive coil, where two solenoids were wound in series [7]. In this work, two different coil topologies are compared: one with a two-section gradiometer design as in [7], and the other with a three-section gradiometer design. We analyze the robustness and efficiency of each setup in terms of the homogeneity of the drive field, the sensitivity profile of the receiver coil, the mutual inductance of the two coils, and power requirements.