| Magnetic Particle Imaging (MPI) is a revolutionary medical imaging platform that uses safe iron oxide nanoparticle tracers to offer fundamentally new capabilities for medical imaging, in applications such as vascular imaging, and ultra-sensitive cancer therapeutics. MPI is the first medical imaging platform to intrinsically exploit nanoscale material properties: in MPI, images are formed from direct measurements of magnetic nanoparticle tracers, whose tunable, size-dependent magnetic properties must be optimized for imaging, by selecting a particular particle size and narrow size-distribution.;We have developed an approach to optimize tracers for an arbitrary imaging system, by: (1) modeling of nanoparticle magnetization in applied AC fields to guide tracer design and interpret experimental results, (2) tailoring of chemical nanoparticle synthesis and preparation to carefully tune particle size while minimizing size distribution, and to coat the synthesized particles with a biocompatible polymer shell, and (3) experimental optimization of biocompatible nanoparticle tracers for MPI, using an MPI magnetometer built to characterize tracer performance. The MPI magnetometer is a zero-dimensional MPI system designed to measure the derivative of time-varying tracer magnetization, M, the critical metric for tracer performance, under applied field conditions similar to MPI imaging. Particular attention will be paid to measurements acquired using this system.;We determined that optimized tracers, with core magnetic diameter of 19nm, narrow size distribution, and hydrodynamic diameter of 44nm, showed 30% better spatial resolution and 3x greater signal intensity than Resovist, a commercial nanoparticle tracer developed for MRI, when the frequency of the applied field was 25 kHz. Finally, while we demonstrated improvements in measurements of intrinsic tracer performance, further improvements are required to achieve theoretical tracer performance; our approach provides a template for future work. |
