4 T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy

Typically P-31 in vivo magnetic resonance spectroscopic studies are limited by SNR considerations. Although phased arrays can improve the SNR; to date P-31 phased arrays for high-field systems have not been combined with P-31 Volume transmit coils. Additionally, to provide anatomical reference for the P-31 studies, without removal of the coil or patient from the magnet, double-tuning (P-31/H-1) of the volume coil is required. In this work we describe a series of methods for active detuning and decoupling enabling use of phased arrays with double-tuned volume coils. To demonstrate these principles we have built and characterized an actively detuneable P-31/H-1 TEM volume transmit/four-channel P-31 phased array for 4 T magnetic resonance spectroscopic imaging (MRSI) of the human brain. The coil can be used either in volume-transmit/array-receive mode or in TEM transmit/receive mode with the array detuned. Threefold SNR improvement was obtained at the periphery of the brain using the phased array as compared to the volume coil. (c) 2007 Elsevier Inc. All rights reserved.