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

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

Magnetic resonance imaging (1997-01-01)
P S Tofts, G J Barker, T L Dean, H Gallagher, A P Gregory, R N Clarke
ABSTRACT

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 epsilon' = 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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Petroleum ether, ACS reagent
Sigma-Aldrich
Petroleum ether, spectrophotometric grade
Sigma-Aldrich
Petroleum ether, ACS reagent
Sigma-Aldrich
Petroleum ether, ACS reagent
Sigma-Aldrich
Petroleum ether, anhydrous