Tracking injectable microspheres in dynamic tissues with encapsulated superparamagnetic iron oxide nanoparticles.

Trackable spheres of similar size to those typically used for sustained protein delivery are prepared by incorporating superparamagnetic iron oxide (SPIO) nanoparticles into the core of poly(lactide-co-glycolide) microspheres. The visibility of injections in static and temporally in dynamic tissue systems is demonstrated. This method improves upon other, less sensitive imaging modalities in their ability to track injectable delivery systems.