Spatially resolved measurement of magnetic nanoparticles using inhomogeneous excitation fields in the linear susceptibility range (<1mT)

Abstract

For small excitation fields in the microtesla (μT) range, the dependency of the magnetic moment of magnetic iron oxide nanoparticles (MNP) on the external field can be regarded as linear. Sensitive superconducting quantum interference devices (SQUIDs) enable the detection of the response of MNP in biological tissue in the pT range. The co-registration of the excitation field is reduced by appropriate geometrical configuration of excitation coil and sensor coil. MNPs in a wide range of mean diameter and distribution parameters can be used for signal generation. The spatial distribution of MNP is reconstructed using data from a parallel multi-sensor and sequential multi-coil arrangement and applying linear estimation techniques. The time delayed response of MNP due to Brownian and Néel relaxation processes represents a specific signal not being influenced by the diamagnetic contribution of water in the tissue. We present the theoretical background and measurement data from different setups that will exemplify the concept.