Performance Consequences of Broken Cylindrical Symmetry for a 7T Head RF Transmit Array

Mikhail Kozlov¹, Robert Turner¹

We numerically simulated a transmit-only strip-line 8-channel 7T RF transmit coil array designed and built by Vaughan. A non-split tuning resonance Sxx can be obtained, despite relatively high (-6dB) adjacent element coupling, but excitation uniformity can be very poor when coupling is asymmetrical. By installing different values at specific capacitor positions it is possible to improve excitation uniformity, but reflected power Parray_refl remains high. For CP mode excitation, decoupling of array elements whilst simultaneously equalizing currents through the front and end capacitors significantly improves transmit performance without improving inhomogeneity. Equalizing element currents does not necessarily improve excitation homogeneity.