Magnetic particle imaging (MPI) is an emerging non-invasive tomographic technique that directly detects superparamagnetic nanoparticle tracers.
MPI systems use changing magnetic fields to generate a signal from superparamagnetic iron oxide (SPIO) nanoparticles.
MPI is often used in combination with anatomical imaging techniques (such as CT or MRI) providing information on the location of the tracer.
The iron oxide tracer used with MPI are cleared naturally by the body through the mononuclear phagocyte system.
[2] The high sensitivity of the technique means it may also be possible to image micro-metastasis through the development of nanoparticles targeted to cancer cells.
MPI is being investigated as a clinical alternative screening technique to nuclear medicine in order to reduce radiation exposure in at-risk populations.
Functional neuroimaging using MPI has been successfully demonstrated[5] in rodents and has a promising sensitivity advantage compared to other imaging modalities.
The tracers used in magnetic particle imaging (MPI) are superparamagnetic iron oxide nanoparticles (SPIONs).
They are composed of a magnetite (Fe3O4) or maghemite (Fe2O3) core surrounded by a surface coating (commonly dextran, carboxydextran, or polyethylene glycol).
[10] However, more recent calculations suggest that there exists an optimal SPIONs magnetic size range (~26 nm) for MPI.
A recent review paper by Chandrasekharan et al. summarizes properties of various iron oxide contrast agents and their MPI performance measured using their in-house Magnetic Particle Spectrometer, shown in the picture here.
Resovist (Ferucarbotran), consisting of iron oxide made via coprecipitation, is the most commonly used and commercially available tracer.
It minimizes unwanted interactions between the iron oxide cores (for example, counteracting attractive forces between the particles to prevent aggregation), increases stability and compatibility with the biological environment, and can also be used to tailor SPION performance to particular imaging applications.
[9][11] Different coatings cause changes in cellular uptake, blood circulation, and interactions with the immune system, influencing how the tracer becomes distributed throughout the body over time.