Analysis of wave behavior in lossy dielectric samples at high field

TLDR

The characteristic image intensity distribution in the human head results from spatial phase distribution and amplitude modulation by interference of RF traveling waves determined by the sample‑coil configuration. The study examines RF field wave behavior and associated nonuniform image intensity at high magnetic field strengths experimentally and numerically. The authors evaluate the RF field from a 10‑cm surface coil at 300 MHz in a 16‑cm spherical phantom with variable salinity and in the human head, validate a numerical calculation method against experimental data, and analyze the field’s behavior across 42–350 MHz relative to average brain electrical properties. Temporal progression of the RF field shows that the standing wave and dielectric resonance occurring in a pure water phantom near 300 MHz are greatly dampened in the human head due to strong electromagnetic wave decay. Published in Magn Reson Med 47:982–989 (2002) and © 2002 Wiley‑Liss, Inc.

Abstract

Abstract Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magnetic field strengths are examined experimentally and numerically. The RF field produced by a 10‐cm‐diameter surface coil at 300 MHz is evaluated in a 16‐cm‐diameter spherical phantom with variable salinity, and in the human head. Temporal progression of the RF field indicates that the standing wave and associated dielectric resonance occurring in a pure water phantom near 300 MHz is greatly dampened in the human head due to the strong decay of the electromagnetic wave. The characteristic image intensity distribution in the human head is the result of spatial phase distribution and amplitude modulation by the interference of the RF traveling waves determined by a given sample‐coil configuration. The numerical calculation method is validated with experimental results. The general behavior of the RF field with respect to the average brain electrical properties in a frequency range of 42–350 MHz is also analyzed. Magn Reson Med 47:982–989, 2002. © 2002 Wiley‐Liss, Inc.