University of Twente Student Theses


Exploring and enhancing the possibilities and performance of a low-field tabletop MRI scanner

Lange, Arthur de (2021) Exploring and enhancing the possibilities and performance of a low-field tabletop MRI scanner.

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Abstract:In western healthcare, Magnetic Resonance Imaging (MRI) is an often used diagnostic tool. The currently used 1.5 or 3 teslas (T) MRI scanners offer great image quality but are expensive to make. Low-field MRI scanners in the range of 0.2-1T are less expensive and thus have great potential for creating cheaper and more accessible healthcare. The main goal of this project is to explore and enhance the possibilities and performance of a new low-field (0.5T) tabletop scanner. To support the main goal, four topics are investigated: the maximum resolution and Signal-to-Noise Ratio (SNR) of the system; accelerated imaging using Compressed Sensing (CS); T2 mapping for tissue classification; and the implementation of fat suppression techniques. The gained knowledge about the scanner is applied to a test case of scanning pig lymph nodes. Some of these nodes are injected with SPIO (Superparamagnetic Iron Oxide) tracer which might be used in the future for the detection of metastasis. The results of this thesis show that the maximum isotropic resolution, while maintaining an acceptable SNR, lies at 0.25mm for a 3D Fast Spin Echo (FSE) sequence. 3D imaging is preferred over 2D for this device, due to an unexpected high difference in SNR. Compressed Sensing is simulated and implemented to accelerate the acquisition of the tabletop scanner. The CS simulations presented in this research show that this technique can accelerate the acquisition up to a factor of 4 while maintaining acceptable image quality (SSIM of ~90%). The implementation of a CS sequence, capturing and reconstructing undersampled data, was successful. The quantitative imaging possibilities of this portable device are tested for classifying tissues using 3D T2 mapping. This technique is compared to 0D T2 mapping. The results for the 3D mapping indicate inaccurate T2 measurements that vary when settings are changed, such as resolution or echo time. Therefore, more advanced correction models will be necessary before using 3D T2 mapping. However, the 0D measurement method shows stable and promising results for T2 determination. Fat suppression was applied to improve the visualisation of the pathology of samples enclosed in adipose tissue, such as lymph nodes. Dixon and STIR methods were successfully implemented for T1- and T2-weighted fat-suppressed imaging. It is recommended to continue the work on CS, since it shows promising results for the entire low-field MRI development. Additionally, the overall stability of the system should be improved by enhancing the field homogeneity and gradient linearity. These stability improvements will enable the use of advanced gradient echo sequences, more accurate T2 and T2* mapping, and less banding artifacts for bSSFP imaging.The results of the lymph node imaging proved that this scanner is capable of creating high-quality 3D MR images. The SPIO inside these nodes can also be visualised with great detail using FSE sequences. Overall, this tabletop scanner is a great addition to MRI education and research.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:33 physics, 44 medicine, 50 technical science in general, 54 computer science
Programme:Biomedical Engineering MSc (66226)
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