Magnetic Particle Imaging (MPI) & Magnetic Particle Spectroscopy (MPS)

Magnetic Particle Imaging (MPI) is a tomographic imaging method that quantitatively visualises the spatial distribution of magnetic nanoparticles (superparamagnetic iron oxides, SPIOs) in real time and without ionising radiation. 

It exploits the non-linear magnetisation response of the particles: by superimposing a static selection field with oscillating drive fields, a field-free region is created whose motion through the field of view spatially encodes the particle signal. Because the tracers are administered as biocompatible suspensions and the method offers high sensitivity together with excellent temporal and good spatial resolution, MPI is particularly suited to angiographic, interventional and functional applications. 

Closely related is Magnetic Particle Spectroscopy (MPS), which measures the particle response in a stationary setup and serves to characterise tracers, validate physical particle models, and efficiently determine the system matrices used for image reconstruction. More generally, it can also be used to determine the physical parameters of magnetic materials, such as their hysteresis, susceptibility and dynamic magnetisation behaviour under the influence of a static field.

Our research follows the entire signal chain – from the physics of the nanoparticles through the hardware to the clinical application.

A particular focus lies on scientific instrumentation and analogue signal processing. This includes low-noise, gradiometric and surface receive coils that increase sensitivity – down to the detection of tracer amounts in the picogram range – as well as receive chains that separate the weak particle signal from the excitation signal, which is orders of magnitude stronger. These hardware concepts were essential building blocks on the path to a human-sized MPI system for brain imaging, which opens the prospect of continuous bedside stroke diagnostics. In preclinical studies, MPI has been used, among other things, to image cerebral perfusion during acute stroke in real time and to detect and monitor intracranial haemorrhage.

At the Metrology Lab we continue this line of work: we combine precise measurement technology, coil and system design, calibration strategies and physical particle modelling to further increase the sensitivity, quantifiability and transferability of MPI and MPS systems – with the goal of bringing the technology closer to robust medical and technical applications.