Optimization of micro antennas for interventional/intravascular MRI

The effective use of MRI for minimally invasive interventional/intravascular procedures has been limited by the availability of hardware that has been optimized for safety and image quality. An interventional procedure typically has three parts---device guidance to the target tissue, application of the intervention, and monitoring of the therapy site. In the first part, patient safety has always been of great concern with the use of active tracking antennas for device guidance. In the second and third parts of the procedure, there has been a lack of optimized intravascular imaging antennas. In this work, these two issues are addressed through the development of a novel detuning technique and through the optimization of the opposed-solenoid imaging coil as well as parallel imaging techniques and modifications to increase longitudinal sensitivity.; A novel active circuit detuning method using optoelectronic technology was first developed to address the issue of device heating from conductive leads. A photoresistor or photodiode is combined with the active tracking circuitry. In conjunction with inductive coupling, conductive leads are eliminated. This technology is then integrated into the MR machine to provide system-controlled detuning.; To address micro imaging antennas, the opposed-solenoid antenna was chosen for its imaging quality, particularly in the acquisition of axial images. Coil construction parameters are optimized through computer simulations, which are then validated by imaging experiments with phantoms and porcine animal models.; To increase acquisition speed, the opposed-solenoid coil is modified to a two-channel array coil for parallel imaging. Computer simulations are used to define construction parameters and animal imaging experiments are used to validate simulation results.; To increase longitudinal coverage, the use of multi-element opposed-solenoid coils and hybrid imaging coils is explored. The spacing between elements in a multi-element solenoid is optimized and the combination of an opposed-solenoid coil with single-loop windings is explored using computer simulations and phantom imaging experiments.; Finally, a comparison of two popular intravascular imaging coils in the axial imaging plane is undertaken. Computer simulations based on the modified filling factor confirm the superiority of the opposed-solenoid over the dipole antenna in this imaging application. Phantom imaging experiments further confirm these findings.