A low dielectric constant customized phantom design to measure RF coil nonuniformity

P.S. Tofts, neurology Barker, T.L. Dean, H. Gallagher, A.P. Gregory, R.N. Clarke

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17 Citations (Scopus)


The selection of a suitable low dielectric constant liquid for radiofrequency coil nonuniformity measurements is described. Measurements of dielectric constant (relative permittivity) were made on a range of candidate liquids. After excluding liquids that were too inflammable or too viscous, Esso Bayol 82 oil (dielectric constant ϵ′ = 2.37) was chosen. At 1.5 T, a 27 cm diameter cylindrical phantom (test object) filled with Bayol 82 has a maximum nonuniformity of 1.9% arising from radiofrequency standing waves. The maximum diameter cylinder that can be used without the nonuniformity exceeding 2% is given for a range of liquids and field strengths. The construction of customized containers that fit closely inside a radiofrequency head coil from glass fiber reinforced resin (“fiberglass”) is described. Thermal expansion of the liquid takes place without a rise in the internal pressure in the container.
Original languageEnglish
Pages (from-to)69-75
Number of pages6
JournalMagnetic Resonance Imaging
Issue number1
Publication statusPublished - Jan 1997


  • dielectric constant, relative permittivity, test object, phantom, nonuniformity, head coil


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