Evaluation of imaging parameters in Magnetic Particle Imaging

Magnetic Particle Imaging (MPI) is a medical imaging modality, that is (in the current state in 2017) in the preclinical stage. It is based on the spatially encoded detection of magnetic nanoparticles that are magnetized by an external magnetic field. Employing gradient fields and pickup coils the particle distribution can be reconstructed from the measurement signal. Body tissue is ignored with this technology. Based the potential high spatial and temporal resolution, MPI is a worldwide topic of research. Besides MPI, the Magnetic Particle Spectroscopy (MPS) has been established for the characterization of magnetic nanoparticles under MPI conditions. Since this method only yields relative information, an MPI scanner is still needed for quantitative estimations regarding the spatial resolution under consideration of the signal-to-noise ratio. This leaves room for optimization. The first part of the thesis describes the influence of the measurement signal on the spatial resolution in MPI. Based on classic theories of signal-processing and imaging, the MPI signal is analyzed regarding the Nyquist-Shannon-Sampling-Theorem and the spatial frequencies and a direct relationship between spatial frequencies and harmonic structure is indicated. Finally, the spatial resolution is related to the harmonics above noise level. In the second part, it is presented based on simulation results how the tracer properties may be optimized for MPI. It is shown, that due to dynamic effects, tracers need to be attuned specifically for MPI via several parameters. Finally, a parameter is presented for the optimization of MNP that is independent of the applied field strength and frequency. In the third and last part of the thesis, an enhancement of the standard MPS characterization is presented to estimate the spatial resolution of the tracer in dependence on the amount of the tracer and its properties. Besides the characterization of several commercially available tracers, the theory from the first part of the thesis is successfully verified. Moreover, a study is presented in which several resolution phantoms were imaged in a commercial MPI-scanner and successfully compared to the previous resolution characterization of the tracer.