Selective actuation and MPI of magnetic beads

Magnetic beads can serve as drug carries or agents for hyperthermia. For a precise treatment, the magnetic beads need to be steered towards their targeted position. Magnetic objects can be moved by either a magnetic gradient field or by a homogeneous magnetic field with a rotating field vector. Both, a gradient field and a homogeneous field, act on all magnetic objects similarly and therefore a selection between various objects is not possible. Here we show a selective actuation of magnetic beads by superimposing a gradient field with a rotating homogeneous field. With the selection field, forming a field free point, and the focus field with rotating field vector of an MPI scanner, selective actuation is performed. Since tomographic imaging is essential for the real-time tracking of the actuation process, we demonstrate the feasibility to visualize the magnetic beads with MPI before and after actuation.