Quantitative and binding-specific imaging of magnetic nanoparticle distributions

Magnetic nanoparticles (MNPs) are intensively tested in novel cancer treatment approaches where they act as drug carriers in magnetic drug targeting or as heat generators in magnetic hyperthermia. For these applications the quantitative knowledge of the MNP distribution side the body is essential. In addition to the location of the MNP, information about the interaction of the MNPs with the biological matrix would be extremely useful. Here, we demonstrate a quantitative imaging experiment for MNPs where in addition to the distribution of MNP concentration also the binding state of the MNPs is visualized. In magnetorelaxometry (MRX) the magnetic relaxation of an MNP ensemble after changing an external magnetization field is utilized for their specific and quantitative detection. The relaxation time is determined by the superposition of Brownian and Néel relaxation processes within the MNP ensemble. Thus, it contains information about the binding state of the MNPs. Recently, we experimentally demonstrated quantitative imaging of an MNP distribution by sequential MRX measurements using spatially varying magnetization field patterns [1]. Here, we extend this approach by a phenomenological data model [2] in order to identify different binding states of the MNPs in the images of the MNP distribution.