title: Analysis of wave behavior in lossy dielectric samples at high field.
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.
authors.affiliation: Center for NMR Research, Department of Radiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA. qyang@psu.edu
authors.forename: Qing X
authors.initials: QX
authors.lastname: Yang
authors.forename: Jinghua
authors.initials: J
authors.lastname: Wang
authors.forename: Xiaoliang
authors.initials: X
authors.lastname: Zhang
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Collins
authors.forename: Michael B
authors.initials: MB
authors.lastname: Smith
authors.forename: Haiying
authors.initials: H
authors.lastname: Liu
authors.forename: Xiao-Hong
authors.initials: XH
authors.lastname: Zhu
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Vaughan
authors.forename: Kamil
authors.initials: K
authors.lastname: Ugurbil
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
mesh_terms: D055590:Electromagnetic Phenomena; D006257:Head / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging