Magnetic field sensitivity at 7-T using dual-helmholtz transmit-only coil and 12-channel receive-only bended coil

The purpose of this study was to combine a dual-Helmholtz (DH) transmit (Tx)-only coil and 12-channel receive (Rx)-only bended phased array (PA) coil to improve the magnetic flux (|B₁ |) sensitivity in the superior-to-inferior (S-I) direction during human brain magnetic resonance imaging (MRI) at 7-T. The proposed coil combination was primarily implemented by electromagnetic (EM) simulation and compared with the 16-leg birdcage coil and 8-channel PA coil, which are generally used for the Tx- and Rx-only modes, respectively. The optimal coil combinations for the proposed structure were determined by |B₁ | field calculations using the |B_T⁺ | and |B_R^- | fields, which are respectively the transmit and receive components of the |B₁ | field. The coil performance was then evaluated by a bench test and 7-T MRI experiment. The results of the computational calculations indicated that the |B_T⁺ | field of the DH coil was distributed similarly to that of the 16-leg birdcage coil despite the fewer conducting legs of the former. However, the 12-channel Rx-only bended PA coil had clearly higher |B_R^- | profiles compared to the 8-channel PA coil. The results of the 7-T in vivo experiment showed that the proposed combination of the DH Tx-only coil and 12-channel Rx-only bended PA coil had better |B₁ | field homogeneity in the sagittal slice as well as higher |B₁ | field sensitivity during human brain MRI compared to an 8-channel Rx-only PA coil. SCANNING 38:515-524, © 2015 Wiley Periodicals, Inc.