Viscosity quantification using multi-contrast magnetic particle imaging

Magnetic particle imaging (MPI) is a relatively new tomographic imaging technique using static and oscillatingmagnetic fields to image the spatial distribution ofmagnetic nanoparticles.The latter being the contrastMPI has been initially designed for. However, recently it has been shown thatMPIcan be extended to amulti-contrast method that allows one to simultaneously image the signals of differentMPI tracer materials. Additionally, it has been shown that changes in the particles environment, e.g. the viscosity have an impact on theMPI signal and can potentially be used for functional imaging. The purpose of the present work is twofold. First, we generalize theMPI imaging equation to describe different multi-contrast settings in a unified framework. This allows for amore precise interpretation and discussion of results obtained by single- andmulti-contrast reconstruction. Second,we propose and validate a method that allows one to determine the viscosity of a small sample from a dual-contrast reconstruction. To this end, we exploit a calibration curve mapping the sample viscosity onto the relative signalweights within the channels of the dual-contrast reconstruction. The latter allows us to experimentally determine the viscosity of the particle environment in the range of 1–51.8mPa swith a relative methodological error of less than 6%.