Xinqiang Yan1,2, Zhipeng Cao1,3, William A Grissom1,2,3,4. 1. Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA. 2. Department of Radiology, Vanderbilt University, Nashville, Tennessee, USA. 3. Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA. 4. Department of Electrical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
Abstract
PURPOSE: To implement and validate low-loss ratio-adjustable power splitters (RAPS) for array-compressed parallel transmission (acpTx). METHODS: In acpTx, 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. Previous networks comprised a bank of power splitters, followed by attenuators to implement the amplitudes of the compression weights for each coil, but this resulted in high power dissipation in the network. Recognizing that an acpTx network need only implement relative attenuations between outputs, a RAPS circuit was developed which combines power splitting and relative attenuation, and has low insertion loss. RAPS circuits were experimentally validated and used to build an array compression network for a one-channel-to-four-coil spiral acpTx excitation experiment. RESULTS: Bench tests showed that the RAPS circuits came within 0.05 dB of the desired output ratios, and power dissipation was approximately 0.5 dB (10%). The spiral excitation experiment showed that the ability to optimally drive four coils with a single channel reduced excitation error by 46% compared to driving one coil, without using attenuators in the array compression network. CONCLUSION: RAPS circuits enable the construction of low-loss array compression networks for parallel transmission. Magn Reson Med 79:2422-2431, 2018.
PURPOSE: To implement and validate low-loss ratio-adjustable power splitters (RAPS) for array-compressed parallel transmission (acpTx). METHODS: In acpTx, 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. Previous networks comprised a bank of power splitters, followed by attenuators to implement the amplitudes of the compression weights for each coil, but this resulted in high power dissipation in the network. Recognizing that an acpTx network need only implement relative attenuations between outputs, a RAPS circuit was developed which combines power splitting and relative attenuation, and has low insertion loss. RAPS circuits were experimentally validated and used to build an array compression network for a one-channel-to-four-coil spiral acpTx excitation experiment. RESULTS: Bench tests showed that the RAPS circuits came within 0.05 dB of the desired output ratios, and power dissipation was approximately 0.5 dB (10%). The spiral excitation experiment showed that the ability to optimally drive four coils with a single channel reduced excitation error by 46% compared to driving one coil, without using attenuators in the array compression network. CONCLUSION: RAPS circuits enable the construction of low-loss array compression networks for parallel transmission. Magn Reson Med 79:2422-2431, 2018.
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