A typical parallel transmit system has an equal number of RF power amplifiers individually connected to an equal number of coil elements. When performing B1+ shimming, the maximum B1+ available is limited by single channel amplifier performance. RF networks which allow for power to be shared between transmit channels have been proposed as a way to overcome this limitation, but fixed networks only offer performance gains over limited ranges of relative phases between channels. Adding a high-power phase shifter between a power-sharing network and coil element can combat this, even with only a few bits of resolution.
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