| Magnetic resonance (MR) imaging (MRI) is a valuable diagnostic imagine modality that has great clinical utility, particularly with the recent migration to higher magnetic fields. In particular, MRI has proven value in image-guided interventions and ablation procedures. Its ability to provide functional information that can increase diagnostic capabilities, such as motion detection, metabolic quantification via spectroscopic imaging, and thermal monitoring, is under investigation. MR physics is based on static and radio-frequency (RF) electromagnetic fields. Associated with such phenomena are inherent resistive and thermal effects that relate both to the signal-to-noise-ratio (SNR) of the received signal, field stability, and to patient safety. This mandates careful development of new hardware and analysis tools for safe and accurate MR procedures, especially at higher field strengths. In this work, new methods are developed and studied to improve MRI image-guided interventions, ablation procedures, thermal mapping, spectroscopic quantification, and patient safety monitoring, with special attention to the newer higher field 3T MRI systems.;The electronic components for a prostate image-guided intervention system designed for use on a 3T MRI scanner were built, and successfully used, in patient procedures for seed placement and biopsies.;A new sequence based on balanced, steady-state free precession (SSFP) was developed to generate relative thermal mapping during hyperthermic procedures. Simultaneous temperature and motion tracking, using CINE harmonic phase HARP analysis [T-HARP], was introduced. The concept of absolute temperature monitoring using RF radiometry in the MRI scanner was also introduced. An original system based on RF filtering was developed for simultaneously monitoring RF heating and MR thermal mapping using an intravascular MR-imaging/RF-heating system to enhance gene therapy under MR guidance. All methods were experimentally tested in phantoms and/or in vivo..;Resistive terms that affect the absolute SNR performance of the loopless antenna used for MR interventions versus field strength were analyzed and shown, unexpectedly, to have quadratic field dependence. The use of 3T guide wires for MR interventions was proven safe and feasible in vivo, as demonstrated in animal studies. Ohmic heating from the system's gradients and the effect on static field stability were studied/corrected for during both MR thermometry and spectroscopy procedures.;A new, safe transmit/receive system for phosphorus (31P) metabolite MR spectroscopy (MRS) quantification was designed for 3T clinical research. Increased RF power requirements at 3T necessitated the development of novel pulses and spectroscopic imaging protocols. A protocol was developed for cardiac 3T 31P MRS and used to measure the metabolite spin-lattice (T1) relaxation times of skeletal and cardiac high-energy phosphate metabolites.;This research resulted, so far, in two patents and several peer-reviewed publications. |
