title: A low dielectric constant customized phantom design to measure RF coil nonuniformity.
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.
authors.affiliation: Institute of Neurology, London, UK.
authors.forename: P S
authors.initials: PS
authors.lastname: Tofts
authors.forename: G J
authors.initials: GJ
authors.lastname: Barker
authors.forename: T L
authors.initials: TL
authors.lastname: Dean
authors.forename: H
authors.initials: H
authors.lastname: Gallagher
authors.forename: A P
authors.initials: AP
authors.lastname: Gregory
authors.forename: R N
authors.initials: RN
authors.lastname: Clarke
mesh_terms: D004129:Dimethylpolysiloxanes / Q000737:chemistry; D004553:Electric Conductivity; D004867:Equipment Design; D005390:Fires; D005898:Glass / Q000737:chemistry; D006801:Humans; D006838:Hydrocarbons / Q000737:chemistry; D007219:Industrial Oils; D007648:Kerosene; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D009682:Magnetic Resonance Spectroscopy; D009821:Oils / Q000737:chemistry; D019047:Phantoms, Imaging; D010938:Plant Oils / Q000737:chemistry; D011091:Polyesters; D011312:Pressure; D012828:Silicones / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013499:Surface Properties; D013816:Thermodynamics; D014783:Viscosity
chemical_list: D004129:Dimethylpolysiloxanes; D006838:Hydrocarbons; D007648:Kerosene; D009821:Oils; D010938:Plant Oils; D011091:Polyesters; D012828:Silicones; D012996:Solutions; C009753:fiberglass; C013089:ligroin; C013830:baysilon