MPI Tracers

Magnetic Particle Imaging (MPI) detects magnetic tracers, many of which are biocompatible and biodegrade in vivo, making them an ideal material for clinical imaging. Superparamagnetic iron oxide (SPIO) nanoparticles are a type of magnetic tracer with a long history in medical imaging, and there are already several FDA and EU-approved formulations. For preclinical use, Magnetic Insight offers a SPIO nanoparticle in two formats, Vivotrax, and Vivotrax Plus.

Magnetic Core Properties

Unlike other imaging approaches, MPI image quality is dependent on the magnetic properties of its tracer. The core diameter, magnetic material, oxidation state, and crystallinity are crucial. This means that advances in the formulation of SPIOs can drive substantial improvements in MPI sensitivity and resolution, independent of any changes in the MPI imaging hardware. This has resulted in significant nanoparticle development efforts by research groups worldwide.

Nanoparticle Coatings

Our ability to use MPI to track the progress of cellular therapy is tied to the development of SPIOs that are stable in cells and remain active for imaging over days to weeks. For example, this can require coatings that prevent cells from degrading SPIOs too quickly while still allowing for robust cell labeling. This has typically involved coatings such as polyethylene glycol (PEG) that prevent nanoparticle aggregation due to magnetic interactions and enhance colloidal stability.

Research into coating and tailoring SPIOs for MPI is an active development area, and there are many degrees of freedom to optimize. Some of these development opportunities are summarized in the figure, showing how flexible magnetic nanoparticles can be for novel targeting mechanisms such as antibodies, proteins, and nucleic acids.

Vivotrax reagent, an iron oxide tracer agent, is sold by Magnetic Insight for pre-clinical use. Prussian blue staining shows cells labeled with Vivotrax.