How Hydrodynamic Fractionation Influences MPI Performance of Resovist

We studied the magnetic resonance imaging liver contrast agent Resovist by a variety of magnetic measurement techniques, in order to understand the physical mechanism of their high magnetic particle imaging (MPI) performance, with a focus on the size-dependent contributions to the MPI signal. To this end, we used asymmetric flow field-flow fractionation to separate Resovist into a set of fractions with defined hydrodynamic diameters. The individual fractions were magnetically characterized by static magnetization and magnetorelaxometry measurements to obtain the corresponding effective magnetic anisotropy and effective size distribution parameters. In addition, the MPI performance of each fraction was assessed by magnetic particle spectroscopy. We observed an MPI signal gain of about 100% with respect to their iron amount for the best fraction. Relating these finding to the results from magnetic characterization provides more insight into the mechanisms of MPI performance of Resovist. This knowledge may help to improve the design of novel MPI tracers.