Simple-to-Fabricate and Water-Stable Instrument Markers for Preclinical Magnetic Particle Imaging and Magnetic Resonance Imaging.

Magnetic Particle Imaging (MPI) is a tracer-based imaging modality with high spatial and temporal resolution, very promising for cardiovascular imaging and peri-interventional guidance. However, most interventional instruments are invisible in MPI due to a lack of signal generation. Existing instrument marking approaches do not address water durability, which is essential for maintaining temporal consistency during experiments. This study aims to develop a simple and water-stable marking technique with smooth surfaces for interventional devices for preclinical MPI and MRI research. Commercial superparamagnetic iron-oxide nanoparticles (SPIONs) were mixed with a transparent varnish and applied to nitinol stents via dip-coating. An impregnation solution was used to seal the markers. The coating was optically evaluated by microscopy. The water-stability of the markers was assessed after 24 hours in water by Magnetic Particle Spectroscopy (MPS) of the surrounding fluid. The imaging performance of the markers was tested in preclinical MPI and MRI systems. Microscopy showed homogeneous SPION distribution and smooth marker surfaces after the sealing. MPS revealed no detectable signal of the water which surrounded the sealed markers, indicating their water-stability. The MPI-scans demonstrated sufficient visualization of individual markers at the stent ends (SNR=11.5). In MRI, susceptibility artefacts of the marked stents were 4.6 times larger compared to unmarked references. The presented technique allows for easy fabrication of instrument markers with commercially available components for preclinical experiments with the magnetic imaging modalities MPI and MRI.