These research projects were aimed at developing new hardware and software technologies for magnetic resonance imaging and spectroscopy at high magnetic field strengths. The advantages of high field strengths are the improved signal to noise ratio, the improved spectroscopic resolution, and the improved contrast for functional imaging studies. The inherent difficulties are the increased magnetic susceptibility effect, which results in field non-uniformity, and the increased dielectric resonant effect of the human body, or the eddy current effect, which causes additional energy loss and signal reduction. The automatic shimming algorithm developed at the 4T whole-body scanner is able to optimize the magnetic field uniformity in any specified region of interest, taking into account the available strengths of the compensation fields. This algorithm has been successfully used in brain imaging and cardiac imaging at 4T. The study in the radiofrequency field distortion from the electromagnetic properties of the body itself at high field strengths was aimed to quantitate this effect, assess its severity at different field strengths, and determine the optimal field strength for cardiac imaging. An experimental technique was developed to map such field distortions in vivo. Computer simulations performed on anatomical models confirmed these measurements. The computer models provide a fast and cost effective way to evaluate a wide range of field strengths. The effect of heartbeat and breathing on propagating radiofrequency waves were directly measured. The frequency response of this effect was recorded. It is being developed into a cardiac monitoring scheme in MR scanners. The information reflected by its complex frequency response is also being studied.
