Design, safety and applications of radio-frequency antennas for ultra-high field MRI of the body

Abstract

Researchers in the field of MRI (Magnetic resonance imaging) are pushing towards the use of stronger and stronger magnets in MRI scanners. These extremely strong magnets are used because the signal-to-noise ratio in MRI scans increases with increasing magnetic field strength. A higher signal-to-noise ratio implies that MRI scans can be acquired at higher resolution. Standard MRI machines operating at a field strength of 3 “Tesla” are able to resolve structures with details up to 1mm, while less common 7 Tesla MRI machines can go to 0.5mm. A few research centers around the world are building MRI scanners with magnets stronger than 7 Tesla, with the aim of imaging the finely detailed structures of the brain and the body. In addition to a very strong static magnetic field, all MRI scanners use radio-frequency (RF) antennas to transmit and receive the signals that generate MRI scans. For MRI scanner operating at ultra-high field strength, the design of these radio-frequency antennas becomes vital to the image quality. If the antennas are not designed or operated properly, the image quality deteriorates. In this thesis, several improvements have been made to RF antennas for body imaging at 7 Tesla and the world’s first 10.5 Tesla. In addition, critical safety aspects of these RF antennas have been studied. The new RF antenna designs are applied to image prostate cancer and the heart at unprecedented resolutions. Finally, the potential gains of MRI scanners operating at even stronger fields (14 Tesla) are demonstrated through a simulation study.