Bimodal Interventional Instrument Markers for Magnetic Particle Imaging and Magnetic Resonance Imaging-A Proof-of-Concept Study.

The purpose of this work was to develop instrument markers that are visible in both magnetic particle imaging (MPI) and magnetic resonance imaging (MRI). The instrument markers were based on two different magnetic nanoparticle types (synthesized in-house KLB and commercial Bayoxide E8706). Coatings containing one of both particle types were fabricated and measured with a magnetic particle spectrometer (MPS) to estimate their MPI performance. Coatings based on both particle types were then applied on a segment of a nonmetallic guidewire. Imaging experiments were conducted using a commercial, preclinical MPI scanner and a preclinical 1 tesla MRI system. MPI image reconstruction was performed based on system matrices measured with dried KLB and Bayoxide E8706 coatings. The bimodal markers were clearly visible in both methods. They caused circular signal voids in MRI and areas of high signal intensity in MPI. Both the signal voids as well as the areas of high signal intensity were larger than the real marker size. Images that were reconstructed with a Bayoxide E8706 system matrix did not show sufficient MPI signal. Instrument markers with bimodal visibility are essential for the perspective of monitoring cardiovascular interventions with MPI/MRI hybrid systems.

Magnetic Particle Imaging: A Resovist Based Marking Technology for Guide Wires and Catheters for Vascular Interventions.

Magnetic particle imaging (MPI) is able to provide high temporal and good spatial resolution, high signal to noise ratio and sensitivity. Furthermore, it is a truly quantitative method as its signal strength is proportional to the concentration of its tracer, superparamagnetic iron oxide nanoparticles (SPIOs), over a wide range practically relevant concentrations. Thus, MPI is proposed as a promising future method for guidance of vascular interventions. To implement this, devices such as guide wires and catheters have to be discernible in MPI, which can be achieved by coating already commercially available devices with SPIOs. In this proof of principle study the feasibility of that approach is demonstrated. First, a Ferucarbotran-based SPIO-varnish was developed by embedding Ferucarbotran into an organic based solvent. Subsequently, the biocompatible varnish was applied to a commercially available guidewire and diagnostic catheter for vascular interventional purposes. In an interventional setting using a vessel phantom, the coating proved to be mechanically and chemically stable and thin enough to ensure normal handling as with uncoated devices. The devices were visualized in 3D on a preclinical MPI demonstrator using a system function based image reconstruction process. The system function was acquired with a probe of the dried varnish prior to the measurements. The devices were visualized with a very high temporal resolution and a simple catheter/guide wire maneuver was demonstrated.

A theranostic agent to enhance osteogenic and magnetic resonance imaging properties of calcium phosphate cements.

With biomimetic biomaterials, like calcium phosphate cements (CPCs), non-invasive assessment of tissue regeneration is challenging. This study describes a theranostic agent (TA) to simultaneously enhance both imaging and osteogenic properties of such a bone substitute material. For this purpose, mesoporous silica beads were produced containing an iron oxide core to enhance bone magnetic resonance (MR) contrast. The same beads were functionalized with silane linkers to immobilize the osteoinductive protein BMP-2, and finally received a calcium phosphate coating, before being embedded in the CPC. Both in vitro and in vivo tests were performed. In vitro testing showed that the TA beads did not interfere with essential material properties like cement setting. Furthermore, bioactive BMP-2 could be efficiently released from the carrier-beads. In vivo testing in a femoral condyle defect rat model showed long-term MR contrast enhancement, as well as improved osteogenic capacity. Moreover, the TA was released during CPC degradation and was not incorporated into the newly formed bone. In conclusion, the described TA was shown to be suitable for longitudinal material degradation and bone healing studies.