Tarama ve geriçatım parametrelerinin manyetik parçacık görüntülemede görüntü kalitesine etkileri

Magnetic particle imaging (MPI) is a novel medical imaging modality, based on the magnetization of the superparamagnetic iron oxide nanoparticles. In MPI, an external magnetic fi eld called the drive fi eld is applied to excite the nanoparticles. The link between the image quality and the drive fi eld parameters is complex, as nanoparticle behaviour changes with the drive field parameters. In addition, the maximum applicable drive field strength is limited by human safety restrictions. Recent studies have shown that the resolution improves at low drive field amplitudes and SNR enhances as drive field frequency increases. Other studies have confi rmed that scanning at frequencies as high as 150 kHz is feasible for human-size MPI scanners. However, how the image quality is affected by drive fi eld parameters, especially for high frequencies around 150 kHz, was not investigated. This thesis investigates the effects of the drive field parameters on the image quality in MPI with relaxometer experiments. The effects of the safety limits are also explored across di fferent drive field frequencies via simulations. The results provide important insight in determining the optimal drive field parameters for safe MPI scanners. This thesis also introduces a new method for improving the image quality in MPI. MPI images can suffer from asymmetric hazing and irregular trending artifacts when nanoparticle response is delayed due to relaxation effects. This thesis proposes a new method based on averaging of relaxation effects from negative and positive half-cycles of the MPI signal, combined with a Savitzky-Golay detrending filter. Both experimental and simulation results demonstrate a signi ficant improvement in image quality.