Investigation of particle mobility in Magnetic Particle Imaging (MPI)

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The project aims for the quantification of the particle mobility in MPS/MPI with the help of defined particle-matrix-systems. Particle mobility is defined via the Brownian time constant and covers the viscosity of the medium and the hydrodynamic volume of the particles. By analyzing interactions and modelling of the signal generation process in MPS/MPI, particle mobility can be deducted from the measured particle signal. The results can be transferred into the imaging system allowing a spatially and timely resolved analysis of the particle-matrix-system (approx. 1 mm resolution and 1 Hz imaging rate). Imaging of the particle mobility considering particle-matrix-interactions is of great importance for numerous biomedical and technological applications. In the project context various particle-matrix-systems (including commercial particles as well as particles from partners in the SPP1681) are to be analyzed. The viscosity of the medium provides a tunable parameter, so that viscous particle-matrix-systems serve as a reference system for particle mobility studies. The degree of determination for viscosity estimation in MPS/MPI can be verified through rheological reference measurements. For the estimation of viscosity from MPS data a calibration-based approach is considered, which requires a viscosity series to be measured and evaluated. Furthermore, we seek to model the viscosity contribution in the MPS signal, which draws a direct connection between the particle mobility and the measurement signal. Applicability of the derived methods for mobility estimation in MPS will be tested against biological particle-matrix-systems, i.e. plasma, cells, tissue. From viscosity studies in MPS, the methods and models will be adopted for Magnetic Particle Imaging. Mobility-aware MPI imaging constitutes an important step towards functional imaging in MPI, where the local nano-/micro-viscosity in a voxel is imaged supplementary to the spatial concentration distribution of the magnetic nanoparticle tracer. The relation between a voxel-averaged macroscopic viscosity and the local mobility of the tracer is of great interest and can be dealt with collectively within the framework of the SPP1681. In practical application scenarios, i.e. in biological media, the quantifiable determination of particle concentration and particle mobility is complicated by non-Newtonian viscosity or viscoelasticity of the particle-matrix-system. A concluding analysis of viscoelastic particle systems and interactions in biological environments is projected.