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Abstract #2620

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

Mikhail Kozlov1, Robert Turner1

1Max Planck Institute for Human Cognitive and Brain Sciences , Leipzig, Saxony, Germany

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.

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Keywords

actual addition adjacent adjusted amplitudes analyzed applying array arrays asymmetric asymmetrical asymmetry attempt balance better bottom brain breaks broken built capacitor capacitors cause channel close cognitive coil column compensation condition conditions consequences consequent cost coupling couplings cylindrical decoupling decrease decreased dedicated degradation delay dense depend dependence despite detail developers dielectric easily element elements enable entire equal equalized equalizing examination excitation excited experimental field fields finding frequency front geometry good greater head hence human improve improved improvement improves increasing individual influence inhomogeneity institute interference jointly laborious larger load loading losses lossy mainly matched matching minimization minimized mode modified negligible network networks noted numerical opposite optimal optimization penalties perfect performance placing position power practically presentation problems provision radiated radiation reflected remained reported respectively roughly rows sequential several shield shimming significantly simulated simulation since spatial step strategy strip studies subject symmetrical symmetry tissue together transmit transverse tuned tuning turner uniformity variation variations window zero