Magnetic particle imaging

Magnetic particle imaging (MPI) is an emerging non-invasive tomographic imaging technique that directly detects the spatial distribution of superparamagnetic nanoparticle tracers. The technology has potential applications in diagnostic imaging and material science. Currently, it is used in medical research to measure the 3-D location and concentration of nanoparticles. Imaging does not use ionizing radiation and can produce a signal at any depth within the body. MPI was invented in 2001 by the industrial scientists Bernhard Gleich and Jürgen Weizenecker, while working at the Hamburg-site of the Philips Research Labs. They published their first system in 2005 and were lateron awarded the prestigious European Inventor Award. Since then, the technology has been advanced by industry as well as academic researchers at several universities in Germany and around the world. From 2011 to 2016, the BMBF-funded MAPIT (Magnetic Particle Imaging Technology) research project was carried out with industrial and academic partners, during which Philips Research in Hamburg built the world's first whole-body scanner. The first commercial MPI scanners for small animals became available from Bruker Biospin in Germany and lateron Magnetic Insight in the United States.

The hardware used for MPI is very different from MRI. Whilst both techniques are based on magnetic fields and use coils to transmit and receive these fields, they differ greatly in technical details such as the geometries of the magnetic fields used, their amplitudes, and their frequencies. MPI systems use changing magnetic fields to generate a signal from superparamagnetic iron oxide (SPIO) nanoparticles. These fields are specifically designed to produce a single magnetic field free point. A signal is only generated at and very near to this point. An image is generated by moving this point across a sample. Since there is no natural SPIO in tissue, a signal is only detected from the administered tracer. This provides images without background. MPI is often used in combination with anatomical imaging techniques (such as CT or MRI) providing information on the location of the tracer.