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Development and analysis of a data acquisition system for a magnetic resonance imaging system
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School of Electrical Engineering |
Master's thesis
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en
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47
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Magnetic Resonance Imaging (MRI) is a widely used and crucial method for clinical diagnosis. MRI images of the head are a critical diagnosis tool for serious conditions such as a brain stroke. MRI is safe, but also an expensive method due to various factors such as the need for cryogenics and high-power electronics in high and ultra-high field strength superconducting MRI devices. A possible solution to overcome the cost and safety issues of high-field MRI devices is to use a low magnetic field. However, lower magnetic fields result in a reduced signal-to-noise ratio leading to a lower resolution as well as artifacts and distortions in the images. The aim of this thesis is to develop a data acquisition system for a prototype low-field MRI device and characterize its main properties. This work involved designing and developing a management console program and integrating a remotely controllable oscilloscope into an existing system. The shimming of the magnet as well as tuning of the acquisition electronics were iteratively adjusted, and programming of sequences and image formation post-processing were developed. The integrated system and subsystems of the prototype were tested to verify functionality. Through iterative tuning of imaging sequence parameters, reasonably strong Free Induction Decay (FID) signals as well as spin echo signals were acquired. A complete imaging sequence using spin echo was developed, and a k-space was obtained through demodulation, filtering, and downsampling. An MRI image of a simple phantom of a syringe filled with tap water was successfully obtained using the inverse Fourier transform. The image had a low resolution and a low signal-to-noise ratio. This thesis demonstrates the feasibility of developing a low-field MRI device and highlights the challenges in achieving adequate image quality.