Local SAR Estimation for Parallel RF Transmit at 7T Using Directional Couplers

Parallel RF Transmit (pTx) in high field MRI is limited by the difficulty in correctly estimating the local specific absorption rate (SAR) given the complicated interferences of the electric field distributions produced by the various elements. Directional couplers allow for current to be measured easily on the transmission line, but parallel matching circuitry transforms the phase and amplitude of the current before entering the element. We propose a method for converting directional coupler values to tx element current values, thus allowing for the correct scaling and linear combination of simulated fields. This is necessary in order to accurately predict local SAR without overly complex simulations.

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