SERIAL transmit - parallel receive (STxPRx) MR imaging produces acceptable proton image uniformity without compromising field of view or SAR guidelines for human neuroimaging at 9.4 Tesla.

PURPOSE: Non-uniform B1+ excitation and high specific absorption rates (SAR) compromise proton MR imaging of human brain at 9.4 T (400.5 MHz). By combining a transmit/receive surface coil array using serial transmission of individual coils with a total generalized variation reconstruction of images from all coils, acceptable quality human brain imaging is demonstrated.
METHODS: B0 is shimmed using sodium MR imaging (105.4 MHz) with a birdcage coil. Proton MR imaging is performed with an excitation/receive array of surface coils. The modified FLASH pulse sequence transmits serially across each coil within the array thereby distributing SAR in time and space. All coils operate in receive mode. Although the excitation profile of each transmit coil is non-uniform, the sensitivity profile estimated from the non-transmit receive coils provides an acceptable sensitivity correction. Signals from all coils are combined in a total generalized variation (TGV) reconstruction to provide a full field of view image at maximum signal to noise (SNR) performance.
RESULTS: High-resolution images across the human head are demonstrated with acceptable uniformity and SNR.
CONCLUSION: Proton MR imaging of the human brain is possible with acceptable uniformity at low SAR at 9.4 Tesla using this serial excitation and parallel reception strategy with TGV reconstruction.