title: Simulations of high permittivity materials for 7 T neuroimaging and evaluation of a new barium titanate-based dielectric.
abstract: High permittivity "dielectric pads" have been shown to increase image quality at high magnetic fields in regions of low radiofrequency transmit efficiency. This article presents a series of electromagnetic simulations to determine the effects of pad size and geometry, relative permittivity value, as well as thickness on the transmit radiofrequency fields for neuroimaging at 7 T. For a 5-mm thick pad, there is virtually no effect on the transmit field for relative permittivity values lower than ∼90. Significant improvements are found for values between 90 and ∼180. If the relative permittivity is increased above ∼180 then areas of very low transmit efficiency are produced. For a 1-cm thick pad, the corresponding numbers are ∼60 and ∼120, respectively. Based upon the findings, a new material (barium titanate, relative permittivity ∼150) is used to produce thin (∼5 mm) dielectric pads which can easily be placed within a standard receive head array. Experimental measurements of transmit sensitivities, as well as acquisition of T(2) - and T 2*-weighted images show the promise of this approach.
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: W M
authors.initials: WM
authors.lastname: Teeuwisse
authors.forename: W M
authors.initials: WM
authors.lastname: Brink
authors.forename: K N
authors.initials: KN
authors.lastname: Haines
authors.forename: A G
authors.initials: AG
authors.lastname: Webb
mesh_terms: D017609:Barium Compounds / Q000737:chemistry*; D001931:Brain Mapping / Q000379:methods*; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009282:Naphthalenesulfonates / Q000737:chemistry; D059906:Neuroimaging / Q000379:methods*; D019047:Phantoms, Imaging; D014025:Titanium / Q000737:chemistry*
chemical_list: D017609:Barium Compounds; D009282:Naphthalenesulfonates; C445092:poly(naphthalenesulfonic acid); C024547:barium titanate(IV); D014025:Titanium