Optimization of the radiative antenna for 7-T magnetic resonance body imaging

Magnetic resonance prostate imaging at 300 MHz is complicated by the effects arising from the short RF wavelength in biological tissue. A radiative antenna leads to a better RF signal penetration for sites located at one or more wavelengths depth, i.e. beyond the near zone. It consists of a dipole antenna placed on a high-dielectric substrate. The effects of changes in substrate dimensions and relative permittivity upon the electromagnetic fields, the B1+ efficiency and the Poynting vector at 10 cm depth are investigated for a realistic body phantom by using electromagnetic simulations. A high relative permittivity substrate is favorable in terms of B1+ efficiency, practical dimensions and weight but it leads to a higher SAR exposure. For optimal B1+ efficiency a relative permittivity in the range of 90 to 110 should be preferred and a minimum thickness of 40 to 50 mm and a width of 50 mm. For optimal local SAR/(B1+)2 ratio, an optimal thickness would be around 50 mm and the width would be as large as possible. This may lead to an impractical element size in terms of weight. (c) 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 43B: 110, 2013