Current and Future Trends in Magnetic Resonance Imaging (MRI)

Human MR imaging to field strengths of 9.4T and higher appears to be possible according to recent data from the University of Minnesota. The Larmor wavelength in the human tissue dielectric at 400 MHz is on the order of 9cm. By conventional methods and thinking, this wavelength would preclude any possibility of achieving safe and successful human imaging. RF interference patterns from a conventional, uniform field volume coil would create severe inhomogeneities in the anatomy. RF losses to the tissue conductor and the tissue dielectric at 400 MHz would result in severe heating for conventional pulse protocols. New methods and technology being developed however at the University of Minnesota not only solve some of these problems, but actually use the short wavelength to great advantage. By controlling the currents in individual RF coil elements, in phase, gain, frequency, time, and space, the RF field can be manipulated to optimize signal from a targeted region of interest for SNR, SAR, CNR, homogeneity, or other criteria. Such "RF shimming" will be automated much like magnetic shimming is today. First examples of these new methods, technologies, and results from them will be presented and discussed in this talk