ADVANCES IN ULTRA-HIGH FIELD 7 TESLA (T) HUMAN MRI: DESIGN AND METHODOLOGY OF TRANSMIT (TX) AND RECEIVE (RX) RADIO FREQUENCY (RF) COILS

Magnetic Resonance Imaging (MRI) is known as non-invasive imaging modality that provides superb anatomical soft tissue details. Over a decade, studies in ultrahigh field (UHF) MRI have been widely carried out in order to further improve the technology as well as understand the diseases. RF coil design and performance studies have been widely conducted to fully utilize the advantages that are given by UHF MRI. The aim of the design is typically producing uniform electromagnetic (EM) field distribution within the volume of interest while lowering the specific absorption rate (SAR) for Tx array and preserving/enhancing high signal to noise ratio (SNR) with Rx array. Clinically available MRI such as 1.5 Tesla (T) and 3T, uses a whole body RF coil that is embedded in the scanner as the field exciter/transmitter, and separate receivers for different parts of the body. This body coil is not available in UHF MRI due to shorter wavelength resulting in inhomogeneous EM field distributions and the large size of the body coil challenges to tune and match the coil at resonant frequency of the UHF MRI, ~300MHz as well as the size of the UHF MRI market is too small that the vendors are not actively investing in the body coil development. Due to the inexistence of the body coil at UHF MRI, it is critical to develop a RF transmit coil systems that produce a uniform B1+ field (clockwise rotating circularly polarized transverse magnetic field that is responsible for excitation) and low specific absorption rate (SAR). Aim of this thesis is to develop and evaluate new design of transmit (Tx) arrays and receive (Rx) arrays for breast and extremity (knee and ankle/foot) MR imaging at 7T. This thesis consists of several articles associated with breast and extremity MR imaging, namely: 1) Experimental and numerical analysis of B1+ field and SAR with a new transmit array design for 7T breast MRI (published as a first author), 2) Development of a 7T RF coil system for breast imaging (published as a first author), 3) Two way - split RF array development for knee MRI at 7T (under preparation as a main author), 4) A new RF Transmit Coil for Foot and Ankle Imaging at 7T MRI (published as a second author), and Overall, the work of this thesis contributes toward the understanding RF coil design and evaluation for UHF MRI human imaging.