Browsing by Author "Bozkurt, Ecem"

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Open Access
Effects of drive field parameters in magnetic particle imaging: A relaxometer study
(IEEE, 2018) Bozkurt, Ecem; Ütkür, Mustafa; Muslu, Yavuz; Sarıtaş, Emine Ülkü
In Magnetic Particle Imaging (MPI), it is possible to acquire signal from the nanoparticles via applying oscillating magnetic fields in the 1 kHz -150 kHz frequency range. Though 25 kHz is commonly used, there are not enough studies on determining the optimal excitation frequency and excitation strength for obtaining images of high quality. In this study, we observed nanoparticles' response and the effect on the point spread functions (PSF) at various field amplitudes and at 10 kHz, 25 kHz and 148.5 kHz excitation frequencies. Accordingly, at 10 kHz and 25 kHz both the harmonic response of the nanoparticles and the PSFs are largely similar. On the other hand, the frequency components at 148.5 kHz are decreasing rapidly at increasing harmonics. The larger full-width at half-maximum of the obtained PSF indicates that the image resolution of this image will be lower at this frequency.
Open Access
Effects of scanning and reconstruction parameters on image quality in magnetic particle imaging
(2018-01) Bozkurt, Ecem
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.
Open Access
Manyetik parçacık görüntüleme için sinyal-gürültü oranını eniyileyen görüntü geriçatım tekniği
(Gazi Universitesi Muhendislik-Mimarlik, 2017) Bozkurt, Ecem; Sarıtaş, Emine Ülkü
Magnetic particle imaging (MPI) is a new biomedical imaging modality that images the spatial distribution of superpamagnetic iron oxide nanoparticles. In MPI, the amplitude of the excitation magnetic field that causes the time-varying magnetization response of the nanoparticles is restricted by the nerve stimulation safety limits. Hence, the region to be imaged is divided into small sections and scanned as overlapping partial fields-of-view. The nanoparticle signal at the excitation frequency is lost during the filtering process of the direct feedthrough signal induced on the receive coil due to the excitation field. To recover this loss, the overlapping partial fields-of-view are merged via utilizing the continuity and positivity of the desired image. In this work, an image reconstruction technique that merges the partial fields-of-view while optimizing the signal-to-noise ratio is proposed. Accordingly, each partial field-of-view must be weighted by the square of the position-dependent scanning speed. Via extensive simulations at various overlap percentages and signal-to-noise ratios, this work demonstrates that the proposed method overcomes the vertical line artifacts caused by the standard MPI reconstruction techniques and improves image quality.