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The frequencies required for ultra-high field (UHF) magnetic resonance imaging (MRI) applications dictate the necessity for higher channel count of transmit arrays to improve the uniformity and efficiency of the transmit magnetic (B ₁^+) field using a parallel transmit system (pTx). Based on the comparison of 8-channel arrays, our previous study suggested the concept of a monopole and dipole hybrid antenna (MDH) array for human head imaging at 10. 5 Tesla (T) MRI. Here we expanded it to a 16-channel MDH array to obtain more uniform B ₁^+ field distribution. Then, we further expanded it to a MDH array with individual floating shields (MDHFS) to extend coverage through the z-direction of MRI. To evaluate these arrays, we compared the B ₁^+ efficiencies of the 16-channel MDH and MDHFS arrays with the same dimensions both in electromagnetic field simulations and experiments at 10. 5 T MRI. Both results revealed that the MDHFS array (0. 52/ 0. 36~ T/ W for the simulation and experiment, respectively) showed ~35% lower peak B ₁^+ efficiency compared to the MDH array (0. 76/ 0. 59~ T/ W for the simulation and experiment, respectively) ). However, compared to the MDH array (~10 cm), the MDHFS array (~20 cm) had longer coverage in the entire phantom. Especially, for human head imaging, simulations indicated a 43. 5% lower specific absorption rate (SAR) and 22. 1% higher SAR efficiency at 10. 5 T with the MDHFS array (0. 26 W/kg and 1. 04~ T/ (W/kg), respectively) compared to the MDH array (0. 46 W/kg and 0. 81~ T/ (W/kg), respectively).
Myung Kyun Woo (Wed,) studied this question.