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Experimental implementation of array‐compressed parallel transmission at 7 tesla
Author(s) -
Yan Xinqiang,
Cao Zhipeng,
Grissom William A.
Publication year - 2016
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26239
Subject(s) - electromagnetic coil , parallel communication , decoupling (probability) , transmission (telecommunications) , computer science , dissipation , electronic engineering , spiral (railway) , acoustics , electrical engineering , physics , telecommunications , engineering , control engineering , thermodynamics , mechanical engineering
Purpose To implement and validate a hardware‐based array‐compressed parallel transmission (acpTx) system. Methods In array‐compressed parallel transmission, a small number of transmit channels drive a larger number of transmit coils, which are connected via an array compression network that implements optimized coil‐to‐channel combinations. A two channel‐to‐eight coil array compression network was developed using power splitters, attenuators and phase shifters, and a simulation was performed to investigate the effects of coil coupling on power dissipation in a simplified network. An eight coil transmit array was constructed using induced current elimination decoupling, and the coil and network were validated in benchtop measurements,B 1 +mapping scans, and an accelerated spiral excitation experiment. Results The developed attenuators came within 0.08 dB of the desired attenuations, and reflection coefficients were −22 dB or better. The simulation demonstrated that up to 3× more power was dissipated in the network when coils were poorly isolated (−9.6 dB), versus well‐isolated (−31 dB). Compared to split circularly‐polarized coil combinations, the additional degrees of freedom provided by the array compression network led to 54% lower squared excitation error in the spiral experiment. Conclusion Array‐compressed parallel transmission was successfully implemented in a hardware system. Further work is needed to develop remote network tuning and to minimize network power dissipation. Magn Reson Med 75:2545–2552, 2016. © 2016 Wiley Periodicals, Inc.