Simulations of high permittivity materials for 7 T neuroimaging and evaluation of a new barium titanate-based dielectric

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 similar to 90. Significant improvements are found for values between 90 and similar to 180. If the relative permittivity is increased above similar to 180 then areas of very low transmit efficiency are produced. For a 1-cm thick pad, the corresponding numbers are similar to 60 and similar to 120, respectively. Based upon the findings, a new material (barium titanate, relative permittivity similar to 150) is used to produce thin (similar to 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 T2- and T?2*-weighted images show the promise of this approach. Magn Reson Med, 2012. (C) 2012 Wiley Periodicals, Inc.