MRI and MRS of the human brain at magnetic fields of 14 T to 20 T: Technical feasibility, safety, and neuroscience horizons

The three goals of this paper are: 1) to evaluate the improvements in technology for increasing magnetic flux density (magnetic field) to 14 T in the next few years and eventually to 20 T; 2) to highlight neuroscience opportunities enabled by these advances; and, 3) to evaluate the physiological and biophysical effects associated with MRI at very high performance levels. Substantial recent advances in magnet technology including superconductor developments enable neuroscience goals that are not obtainable at contemporary magnetic fields. Ten areas of brain neuroscience include potential improvements in resolution for functional MRI(BOLD), diffusion weighted MRI, tractography, susceptibility weighted MR, neuronal architecture patterns related to human behavior, proton spectroscopy of small brain biochemicals, chemical exchange saturation transfer (CEST), dynamic contrast enhanced MRI, brain energy metabolism using C-13, O-17, and P-31; and brain electrolyte physiology using Na-23, Cl-35, and K-39. Physiological phenomena and safety aspects include: absorbed RF power, acoustic sound pressure levels, induced electric fields, Lorentz forces, magnetohydrodynamic forces, and biophysical phenomena in cells and tissues. Where feasible, effects are quantified for magnetic fields beyond 7 T with the conclusion that there are no foreseen barriers either in the technical or human safety aspects of brain MRI and MRS at fields up to 20 T. This conclusion is conditioned on results of recommended experiments to verify the predicted level of physiological effects beyond 9.4 T. This technology is predicted to enable quantification of biochemical components of the functioning brain not detectable heretofore.