A device for measuring the trajectory dependent magnetic particle performance for MPI

In ferrofluids, the magnetization undergoes magnetic relaxation processes, which are affected by the concentration of the fluid, the viscosity of the medium, the strength and frequencies of an external magnetic field and the structure of the magnetic core [1,2]. In many models the particles are assumed to have an uniaxial anisotropy that results in one preferred magnetization direction called the easy axis. If the particles are exposed to a magnetic field that is aligned with this easy axis, the corresponding signal response is higher compared to other excitation directions [3]. For a one dimensional excitation this alignment will be reached shortly if the particle is able to mechanically rotate and the hydrodynamic friction is low. In more dimensional excitations, such as in dynamic field free line (FFL) scanners, or in field free point (FFP) scanners, the excitation direction changes constantly [4]. If this change in direction exceeds the maximum mechanical rotation speed of the particles, they are not able to align. As a result, the particle signal will drop. In this work, we present a new device that is able to generate FFP and FFL field sequences while applying different possible offset fields.