Effects of scanning and reconstruction parameters on image quality in magnetic particle imaging
Author(s)
Advisor
Çukur, Emine Ülkü SarıtaşDate
2018-01Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
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 field called the drive field is applied to excite the
nanoparticles. The link between the image quality and the drive field parameters
is complex, as nanoparticle behavior 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 confirmed 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 field 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 different 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 significant improvement in image quality.
Keywords
Magnetic Particle ImagingDrive Field Parameters
Image Reconstruction
Magnetic Field Safety Limits