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Characterization of a dielectric phantom for high‐field magnetic resonance imaging applications
Author(s) -
Duan Qi,
Duyn Jeff H.,
Gudino Natalia,
de Zwart Jacco A.,
van Gelderen Peter,
Sodickson Daniel K.,
Brown Ryan
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4895823
Subject(s) - dielectric , materials science , imaging phantom , permittivity , nuclear magnetic resonance , conductivity , pulse sequence , analytical chemistry (journal) , composite material , optics , optoelectronics , chemistry , physics , chromatography
Purpose: In this work, a generic recipe for an inexpensive and nontoxic phantom was developed within a range of biologically relevant dielectric properties from 150 MHz to 4.5 GHz.Methods: The recipe includes deionized water as the solvent, NaCl to primarily control conductivity, sucrose to primarily control permittivity, agar–agar to gel the solution and reduce heat diffusivity, and benzoic acid to preserve the gel. Two hundred and seventeen samples were prepared to cover the feasible range of NaCl and sucrose concentrations. Their dielectric properties were measured using a commercial dielectric probe and were fitted to a 3D polynomial to generate a recipe describing the properties as a function of NaCl concentration, sucrose concentration, and frequency.Results: Results indicated that the intuitive linear and independent relationships between NaCl and conductivity and between sucrose and permittivity are not valid. A generic polynomial recipe was developed to characterize the complex relationship between the solutes and the resulting dielectric values and has been made publicly available as a web application. In representative mixtures developed to mimic brain and muscle tissue, less than 2% difference was observed between the predicted and measured conductivity and permittivity values.Conclusions: It is expected that the recipe will be useful for generating dielectric phantoms for general magnetic resonance imaging (MRI) coil development at high magnetic field strength, including coil safety evaluation as well as pulse sequence evaluation (includingB 1 +mapping,B 1 +shimming, and selective excitation pulse design), and other non‐MRI applications which require biologically equivalent dielectric properties.