Premium
Ventricular B 1 + perturbation at 7 T – real effect or measurement artifact?
Author(s) -
Brink Wyger M.,
Börnert Peter,
Nehrke Kay,
Webb Andrew G.
Publication year - 2014
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.3112
Subject(s) - cerebrospinal fluid , lateral ventricles , electrical resistivity and conductivity , white matter , dielectric , nuclear magnetic resonance , physics , electromagnetic field , chemistry , materials science , magnetic resonance imaging , anatomy , medicine , pathology , radiology , optoelectronics , quantum mechanics
The objective of this work was to explore the origin of local B 1 + perturbations in the ventricles measured at 7 T. The B 1 + field in the human brain was mapped using four different MRI techniques: dual refocusing echo acquisition mode (DREAM), actual flip‐angle imaging (AFI), saturated double‐angle method (SDAM) and Bloch–Siegert shift (BSS). Electromagnetic field simulations of B 1 + were performed in male and female subject models to assess the dependence of the B 1 + distribution on the dielectric properties of cerebrospinal fluid and subject anatomy. All four B 1 + mapping techniques, based on different B 1 + encoding mechanisms, show ‘residual’ structure of the ventricles, with a slightly enhanced B 1 + field in the ventricles. Electromagnetic field simulations indicate that this effect is real and arises from the strong contrast in electrical conductivity between cerebrospinal fluid and brain tissue. The simulated results were in good agreement with those obtained in three volunteers. Measured local B 1 + perturbations in the ventricles at 7 T can be partially explained by the high contrast in electrical conductivity between cerebrospinal fluid and white matter, in addition to effects related to the particular B 1 + measurement technique used. Copyright © 2014 John Wiley & Sons, Ltd.