Enhanced Methods to Estimate the Efficiency of Magnetic Nanoparticles in Imaging.

Ann Hirt,Alexander Kraupner,David Heinke,Monika Kumari

doi:10.3390/molecules22122204

Abstract

Magnetic resonance imaging (MRI) and magnetic particle imaging (MPI) are powerful methods in the early diagnosis of diseases. Both imaging techniques utilize magnetic nanoparticles that have high magnetic susceptibility, strong saturation magnetization, and no coercivity. FeraSpinTM R and its fractionated products have been studied for their imaging performances; however, a detailed magnetic characterization in their immobilized state is still lacking. This is particularly important for applications in MPI that require fixation of magnetic nanoparticles with the target cells or tissues. We examine the magnetic properties of immobilized FeraSpinTM R, its size fractions, and Resovist®, and use the findings to demonstrate which magnetic properties best predict performance. All samples show some degree of oxidation to hematite, and magnetic interaction between the particles, which impact negatively on image performance of the materials. MRI and MPI performance show a linear dependency on the slope of the magnetization curve, i.e., initial susceptibility, and average blocking temperature. The best performance of particles in immobilized state for MPI is found for particle sizes close to the boundary between superparamagnetic (SP) and magnetically ordered, in which only Néel relaxation is important. Initial susceptibility and bifurcation temperature are the best indicators to predict MRI and MPI performance.

Highlights

Iron oxide nanoparticles have attracted enormous interest in biomedical imaging, i.e., magnetic resonance imaging (MRI) and magnetic particle imaging (MPI) [1,2,3,4]
The tuning of iron oxide nanoparticles as a contrast agent for MRI and tracer in MPI can enhance the visibility of images
It has been shown that superparamagnetic behavior and high magnetic moment are desirable for both MRI and MPI [5,6,7]

Summary

Introduction

Iron oxide nanoparticles have attracted enormous interest in biomedical imaging, i.e., magnetic resonance imaging (MRI) and magnetic particle imaging (MPI) [1,2,3,4]. The tuning of iron oxide nanoparticles as a contrast agent for MRI and tracer in MPI can enhance the visibility of images. It is important, to understand how a material’s physical properties affect its magnetic properties. The magnetic properties of a material will depend upon the particles’ chemical composition, size, shape and whether there is any magnetic interaction amongst the particles [3,8]. Chemical composition will determine to a large extent the saturation magnetization of a material. Magnetite (Fe3 O4 ) has a saturation magnetization (MS ) of 92 Am2 kg−1 , whereas oxidizing the ferrous iron in its structure to ferric iron leads to the formation of either maghemite (γ-Fe2 O3 ) with MS of around 70 Am2 kg−1 , or hematite (α-Fe2 O3 ) with MS of around 0.4 Am2 kg−1

Methods

Results

Conclusion