Improved field homogeneity for multi-channel stepped impedance microstrip transceiver arrays and travelling wave for MRI at 7T

A multi-element microstrip transceiver array is a promising approach for magnetic resonance imaging (MRI) at 7T (298 MHz). Travelling wave (TW) MRI is another method where the RF magnetic field B1+ is carried by propagating circularly polarized modes excited from an antenna located at one end of the MRI system bore. In this paper, full-wave electromagnetic (EM) simulations were performed for an 8-element stepped impedance resonators (SIRs) coil array combined with a circularly polarized patch antenna loaded with a spherical dielectric phantom (0 = 17 cm). An optimization routine was developed to homogenize and maximize the B1
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field inside the phantom. The results yield a combined B1+ field that is 1.3 times higher than the field of a sole 8-element SIRs volume coil and 3.5 times higher compared to the TW approach only. The B1
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field homogeneity for the 8-element SIRs volume coil is much better than for the TW approach only, where the E-field is about 2.3 times higher than the use of a sole 8-element SIRs coil array. After optimizing the combined B1
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field with amplitude/phase control, the B1
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field homogeneity was improved by 67% and 91% in the central transversal and sagittal slices, respectively.