Dielectric Resonance Phenomena in Ultra High Field MRI

Abstract

Theoretical results demonstrate that distilled water can sustain dielectric resonances in head-sized spheres near 200 and 360 MHz, but the presence of significant conductivity suppresses these resonances. These findings are confirmed experimentally with proton images of water and saline (0.05 and 0.125 M NaCl). For lossy phantoms, coupling between the source and phantom overwhelms the dielectric resonance. Because of their low relative permittivity, mineral oil phantoms with 20 cm diameter do not exhibit dielectric resonances below approximately 900 MHz. Significant dielectric resonances were not observed in human head images obtained at 1.5, 4.7, and 8 T.