Lateral Movement of Helical Swimmers Visualized with Magnetic Particle Imaging

The magnetic manipulation of medical devices such as catheters, small cameras or drug filled capsules enables to improve the precision of minimally invasive surgery. Catheters can be steered towards tissue regions difficult to access. Drugs can be delivered directly to cancerous tissue or inflammatory regions, which allows lower dosages and healthy tissue is less affected. In-vitro experiments can be easily visualized with video and microscopy methods, but in-vivo the manipulation process needs to be imaged with a tomographic real time imaging technique to facilitate image guided interventions. Here, Magnetic Particle Imaging (MPI) is a promising method. MPI images the spatial distribution of superparamagnetic nanoparticles. It is highly sensitive and enables real time imaging with a resolution in the submillimeter range. It is based on the nonlinear response of the particles to alternating magnetic fields. A gradient field forming a field free point encodes the signal spatially. A commercially available MPI scanner (Bruker Biospin MPI 25/20 FF) features homogeneous offset fields, called focus fields, applicable in three dimensions to enlarge the field of view. By applying an alternating current to the focus field coils, a rotating magnetic field of up to 10Hz can be generated. These rotating focus fields can be used to manipulate magnetic material inside the MPI scanner, since the materials’ magnetization and the rotating fields induce a torque. This enables dual use of existing MPI scanners for imaging and manipulation. Helical swimmers are being presented, which perform a lateral movement induced by the rotating focus fields inside the preclinical MPI scanner. The swimmers are 3D printed. The material is further investigated in terms of suitability for MPI as well as the geometry of the swimmers aiming at a stable rotation and large propulsion in a water filled phantom.