Browsing by Subject "Rapid imaging"

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Open Access
Compressed sensing techniques for accelerated magnetic resonance imaging
(2017-07) Ilıcak, Efe
Magnetic resonance imaging has seen a growing interest in the recent years due to its non-invasive and non-ionizing nature. However, imaging speed remains a major concern. Recently, compressed sensing theory has opened new doors for accelerated imaging applications. This dissertation studies compressed sensing based reconstruction strategies for accelerated magnetic resonance imaging, speci cally for angiography and multiple-acquisition methods. For magnetic resonance angiography, we propose a novel approach that improves scan time e ciency while suppressing background signals. In this study, we attain high-contrast angiograms from undersampled data by utilizing a two-stage reconstruction strategy. Simulations and in vivo experiments demonstrate that the developed strategy is able to relax trade-o s between image contrast and scan e ciency without compromising vessel depiction. For multiple-acquisition balanced steady state free precession imaging, we develop a framework that jointly reconstructs undersampled phasecycled images. This approach is able to improve banding artifact suppression while maintaining scan e ciency. Results show that the proposed method is able to attain high-quality reconstructions even at high acceleration factors. Overall, the ndings presented in this thesis indicate that compressed sensing reconstructions represent a promising future for rapid magnetic resonance imaging. Consequently, compressed sensing reconstruction techniques hold a great potential to change the time-consuming clinical imaging practices.
Open Access
Safety limits & rapid scanning methods in magnetic particle imaging
(2017-07) Demirel, Ömer Burak
Magnetic Particle Imaging (MPI) is a new imaging modality that utilizes nonlinear magnetization of superparamagnetic tracers, with high sensitivity and zeroionizing radiation advantages. Since the introduction of MPI in 2005, there have been substantial contributions to pre-clinical applications such as cancer imaging, cell tracking, and angiography. These studies have promising implications for future clinical human-sized MPI systems. However, the time-varying magnetic fields that are used during image acquisition are subject to human safety concerns, especially in applications that require rapid imaging. By forming electric field patterns in the body, these fields may result in peripheral nerve stimulation, also known as magnetostimulation. To prevent potential stimulations; the effects of frequency, duration, and direction of the fields, as well as body part size were previously investigated. This thesis investigates the effects of duty cycle and fat/water tissue ratio on magnetostimulation thresholds for the drive field in MPI. Human subject experiments with in-house magnetostimulation setup were conducted at 25 kHz, followed by anatomical Magnetic Resonance Imaging (MRI) of the subjects. Accordingly, magnetostimulation thresholds first decrease then increase with increasing duty cycle and reach a maximum at 100% duty cycle. The results also show that the thresholds are strongly correlated with fat/water tissue ratio. Finally, this thesis also demonstrates that MPI image quality can be preserved for rapid scanning scenarios within the human safety limits.