Session 31: Imaging and image processing III – Nanoparticle imaging and MRI

Abstract

In 2005, B. Gleich and J. Weizenecker initially presented the promising new tracer based medical imaging modality Magnetic Particle Imaging (MPI). It uses the nonlinear magnetization behavior of particles consisting of an iron oxide core coated with dextrane (super paramagnetic iron oxide nanoparticles, SPIONs). MPI has the potential to perform real-time imaging in the sub millimeter-range without the use of harmful radiation. To acquire a particle signal from the tracer, an alternating homogenous magnetic field (drive field) is applied. Due to the nonlinearity of the particle magnetization, the magnetic field is distorted and higher harmonics are generated that indicate a particle concentration within the field of view (FOV). To gain the spatial distribution, another magnetic field that exhibits a high gradient is applied simultaneously. This second field is called selection field. Basically, there are two different types of selection fields. The first approach uses a constant magnetic gradient field containing a field-free point (FFP). Only SPIONs within the close vicinity of the field-free point contribute to the particle signal because all other particles within the FOV are magnetically saturated. As the FFP is moved by the drive field through the FOV a spatial distribution can be obtained. The second approach uses a rotatable field-free line (FFL) that is additionally translated by the drive field to obtain one dimensional projections for various angles. The advantage of the FFL approach is a higher signal quality at equal size and gradient strength while a drawback is a higher power consumption and a more complex coil topology to generate, rotate and translate the FFL. In this work, the currently world's largest FFL MPI Scanner is investigated. Single components of the generated magnetic field are measured precisely to accomplish an accurate simulation of a translating and rotating fieldfree line.