# Evaluation of 8-Channel Radiative Antenna Arrays for Human Head Imaging at 10.5 Tesla  
[PERSON]  
1 Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA; [EMAIL_ADDRESS] (M.K.W.); [EMAIL_ADDRESS] (L.D.); [EMAIL_ADDRESS] (M.T.W.); [EMAIL_ADDRESS] (V.W.P.); [EMAIL_ADDRESS] (R.L.L.); [EMAIL_ADDRESS] (S.J.); [EMAIL_ADDRESS] (Y.E.); [EMAIL_ADDRESS] (K.U.)  
[PERSON]  
1 Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA; [EMAIL_ADDRESS] (M.K.W.); [EMAIL_ADDRESS] (L.D.); [EMAIL_ADDRESS] (M.T.W.); [EMAIL_ADDRESS] (V.W.P.); [EMAIL_ADDRESS] (R.L.L.); [EMAIL_ADDRESS] (S.J.); [EMAIL_ADDRESS] (Y.E.); [EMAIL_ADDRESS] (K.U.)  
[PERSON]  
1 Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA; [EMAIL_ADDRESS] (M.K.W.); [EMAIL_ADDRESS] (L.D.); [EMAIL_ADDRESS] (M.T.W.); [EMAIL_ADDRESS] (V.W.P.); [EMAIL_ADDRESS] (R.L.L.); [EMAIL_ADDRESS] (S.J.); [EMAIL_ADDRESS] (Y.E.); [EMAIL_ADDRESS] (K.U.)  
[PERSON]  
1 Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA; [EMAIL_ADDRESS] (M.K.W.); [EMAIL_ADDRESS] (L.D.); [EMAIL_ADDRESS] (M.T.W.); [EMAIL_ADDRESS] (V.W.P.); [EMAIL_ADDRESS] (R.L.L.); [EMAIL_ADDRESS] (S.J.); [EMAIL_ADDRESS] (Y.E.); [EMAIL_ADDRESS] (K.U.)  
[PERSON]  
1 Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA; [EMAIL_ADDRESS] (M.K.W.); [EMAIL_ADDRESS] (L.D.); [EMAIL_ADDRESS] (M.T.W.); [EMAIL_ADDRESS] (V.W.P.); [EMAIL_ADDRESS] (R.L.L.); [EMAIL_ADDRESS] (S.J.); [EMAIL_ADDRESS] (Y.E.); [EMAIL_ADDRESS] (K.U.)  
generated by an RF coil) patterns, as well as a favorable direction of energy propagation (Poynting vector), which results in greater penetration depth. Consequently, both dipole antennas and the combination of loops with dipole antennas have been successfully used for UHF human imaging applications with high penetration, efficiency, and SNR [17; 18; 19]. However, for realistic head array housings, the coaxial feed cables for dipole antennas have to be routed in close proximity to one leg of the dipole and they interact with the antenna elements.  
In a recent publication [8], we had started to evaluate alternative antenna arrays and compared 16-channel dipole and sleeve antenna arrays. Since intra-element coupling due to the tight spacing of the 16 channels can negatively affect the overall antenna array performance, for the study presented here, we compared more sparsely spaced 8-channel arrays. For an 8-channel dipole antenna head array, we first compared an 'ideal' coil (Figure 1a) without coaxial cables with a realistic array, which included coaxial cables (Figure 1c), in simulations, and evaluated the effect of coaxial feed cables on the dipole antenna performance. To investigate the influence of this effect experimentally, we built an 8-channel dipole antenna head array and compared two setups: one with a more ideal--but, in practice, unrealistic--coaxial feed cable path (Figure 1e) and the other with a realistic close-proximity coaxial feed cable path (Figure 1g). This allowed us to compare the performance of the 8-channel dipole antenna array with a defined phantom load, both in electromagnetic (EM) simulations and 10.5 T MR experiments with the phantom. To evaluate alternative antenna layouts with possibly more advantageous coaxial feed points for head imaging, we built two end-fed antenna arrays: an 8-channel monopole antenna array [20; 21] and an 8-channel sleeve antenna array [8]. Then, we compared the B1\({}^{+}\) efficiency (defined as B1\({}^{+}\) field normalized by the square root of net input power) and specific absorption rate (SAR) efficiency (defined as B1\({}^{+}\)/\(\surd\)(peak 10 g SAR)) of the 8-channel dipole, monopole, and sleeve antenna arrays with the phantom. Finally, we compared the performance of these arrays with a human model.