Fabrication of Radio Frequency Resonators in High Field Magnetic Resonance Imaging
Open Access
- Author:
- Lee, Gangchea
- Graduate Program:
- Bioengineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 19, 2018
- Committee Members:
- Thomas Neuberger, Dissertation Advisor/Co-Advisor
Thomas Neuberger, Committee Chair/Co-Chair
Nanyin Zhang, Committee Member
Siyang Zheng, Committee Member
Michael T Lanagan, Outside Member - Keywords:
- Magnetic Resonance Imaging
Radio Frequency Coil - Abstract:
- Magnetic resonance imaging (MRI) is one of the major medical imaging diagnostic tool in today’s daily clinical routine. This technique produces either two-dimensional (2D) or three-dimensional (3D) images with high resolution and contrast predominantly in soft tissues non-invasively, therefore, providing physiological information that other imaging modality cannot offer. The quality of a MRI image often depends on the signal to noise ratio (SNR), and the high SNR can be sacrificed to achieve either higher resolutions or shorter acquisition times. Therefore, MR research is striving for the highest achievable SNR in the images. There are two major ways to achieve higher SNR: 1) the use of higher static magnetic fields (B0), or 2) the use of optimized radiofrequency (RF) resonator for the image acquisition. However, the optimization of RF resonators at higher B0 becomes harder as the working frequency of the RF resonator increases proportional to B0 (radiation losses, lumped element losses, coil to cable interactions, low quality factors, and dielectric effect becomes problematic at high frequencies). This dissertation describes conventional RF resonator designs and new concepts of RF resonators at a very high magnetic field of 14.1 T. Proton MRI will be conducted on selected biological applications requiring the RF resonator to operate at 600 MHz. The fabrication of conventional coils – a surface coil, a birdcage coil, and scroll coils – is described in the earlier chapters (chapter 2, 3, 4). These coils were fabricated to image the mouse eye in vivo, the mouse brain in vivo, and fixed 3D printed cell strands respectively. Simultaneous imaging concept is also elaborated in chapter 4. In the later chapters (chapter 5, 6), two unconventional design RF resonators – a dielectric resonator, and a patch antenna – were fabricated, tested, and compared with state of the art RF resonators to investigate the possibility of substituting the conventional RF resonators. These two designs provided higher homogeneity but less SNRs. Therefore, improvements to be made to increase SNR are discussed in each chapter.