Control of radiated emissions during MRI using parallel transmit: a path to eliminating the Faraday shielded room for...

High costs remain a significant barrier to the broader adoption of MRI systems. Eliminating the need for Faraday shielding would substantially lower installation costs and facilitate diverse deployment, but this necessitates controlling both the incoming electromagnetic (EM) interference detected by the receive (Rx) system and the outgoing EM radiation from the transmit (Tx) system, usually a body Tx coil. Multiple strategies exist to detect and mitigate the Rx interference, but little progress has been made in mitigating the Tx radiation. This study introduces a parallel transmit (pTx) strategy for reducing Tx radiation to below regulatory limits. At 0.5T, conventional circularly polarized (CP) birdcage coils produce H-field emissions at a 10-meter radius (H_10m) that far exceed the IEC regulatory limit of 8.5 dBµA/m. We model the ability of a 2×8-channel pTx body array at 0.5T which leverages the additional degrees of freedom in arbitrary trajectory pTx pulse design to constrain radiated H_10m. We employ optimal control theory to design arbitrary RF and gradient waveforms with constraints on H_10m, using methods analogous to those for constraining local specific absorption rate (SAR) during pTx. Our simulations demonstrate that the pTx system can reduce peak H_10m by up to 89% and improve flip-angle uniformity by 6-fold compared to the quadrature body birdcage coil and demonstrate a viable approach to mitigating RF-radiation from MRI systems operated without Faraday shielding.