Patrick W Goodwill 

Magnetic Particle Imaging (MPI) is an emerging tracer imaging technique that directly detects superparamagnetic iron oxide (SPIO) nanoparticles with exceptional contrast and high sensitivity at millimeter-scale resolutions.¹ MPI’s contrast is similar to nuclear medicine, but without the complex workflow, safety, and half-life limitations of a radioactive tracer. These capabilities help fill in some of the gaps of current technologies and position MPI as complementary to anatomical imaging techniques such as MRI and X-ray/CT.

The magnetic properties of the nanoparticle tracers seen by MPI define the technique’s image resolution and sensitivity. This is because the MPI signal arise from the interaction between a magnetic nanoparticle, a strong magnetic field gradient, and a time varying magnetic drive field.^2,3  To improve MPI’s spatial resolution, we and others have researched SPIOs with varying core diameters, since Langevin steady-state physics predicts a cubic resolution improvement with increasing SPIO core size. This effort has already produced exciting results, effectively reducing the FWHM resolution by a factor of two and increasing sensitivity an order of magnitude.⁴ However, much remains unknown about the physical mechanisms and trade-offs for further improvements.

Our group and others have begun testing MPI on animal models. We have used long circulating PEG coated nanoparticles to image the brain, detect cancers,⁵ detect gut bleeds,⁶ and visualize traumatic brain injury.⁷ MPI’s high sensitivity also makes it well suited for cell tracking. For example, we have tracked therapeutic neural stem cells for three months⁸ and the biodistribution of mesenchymal stem cells post administration.⁹ In the future, we see opportunities for MPI tracking of immune therapies or immune cells to sites of inflammation such as cancer.

Location:
San Jose, California
95131