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Magnetic nanoparticles are gaining increasing attention as a promising alternative to gadolinium-based contrast agents in magnetic resonance imaging, primarily due to their low toxicity. In this study, we investigated the use of magnetic iron oxide nanoparticles in mouse models of intestinal inflammation to assess their potential for detecting changes in the extracellular matrix. For magnetic quantification, we employed magnetic particle spectroscopy, which offers high sensitivity and minimal interference from biological tissue. However, we observed significant variations in magnetic signals within the intestine, as well as measurable signals in control animals, indicating possible magnetic contamination. By doping the nanoparticles with europium, we were able to confirm this suspicion through quantitative elemental analysis. Examination of mouse feed and feces allowed us to identify the source of contamination. Based on these findings, we developed a method to reliably distinguish genuine signals of magnetic nanoparticles from those caused by external magnetic contaminations. This approach is essential to ensure reliable results in future diagnostic and preclinical research.
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, wirh a focus on the size-dependent contributions of 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 mechanisms of MPI performance of Resovist. This knowledge may help to improve the design of novel MPI tracers.
Resovist® originally developed as a clinical liver contrast agent for Magnetic Resonance Imaging exhibits also an outstanding performance as a tracer in Magnetic Particle Imaging (MPI). In order to study the physical mechanism of the high MPI performance of Resovist®, we applied asymmetric flow fieldflow fractionation (A4F) and static magnetic fractionation (SMF) to separate Resovist® into a set of fractions with defined size classes. As A4F based on an elution method separates MNP according to their hydrodynamic size, SMF fractionates a particle distribution by its magnetic moment. The obtained fractions of both separation techniques were then magnetically characterized by magnetorelaxometry measurements to extract the corresponding effective magnetic anisotropy and hydrodynamic size distribution parameters. Additionally, the MPI performance of each fraction was assessed using magnetic particle spectroscopy. With both separation techniques fractions (normalized to their iron amount) an MPI signal gain of a factor of two could be obtained, even though the distribution of effective anisotropy and hydrodynamic size were significantly different. Relating these findings to the results from magnetic characterization allows for a better understanding of the underlying mechanisms of MPI performance of Resovist®. This knowledge may help to improve the design of novel MPI tracers and development of separation methods.
