Optimized 31P MRS in the human brain at 7T with a dedicated RF coil setup

Abstract

The design and construction of a dedicated RF coil setup for human brain imaging (1H) and spectroscopy (31P) at ultra-high magnetic field strength (7T) is presented. The setup is optimized for signal handling at the resonance frequencies for 1H (297.2MHz) and 31P (120.3MHz). It consists of an eight-channel 1H transmit-receive head coil with multi-transmit capabilities, and an insertable, actively detunable 31P birdcage (transmit-receive and transmit only), which can be combined with a seven-channel receive-only 31P array. The setup enables anatomical imaging and 31P studies without removal of the coil or the patient. By separating transmit and receive channels and by optimized addition of array signals with whitened singular value decomposition we can obtain a sevenfold increase in SNR of 31P signals in the occipital lobe of the human brain compared with the birdcage alone. These signals can be further enhanced by 30±9% using the nuclear Overhauser effect by B1-shimmed low-power irradiation of water protons. Together, these features enable acquisition of 31P MRSI at high spatial resolutions (3.0cm3voxel) in the occipital lobe of the human brain in clinically acceptable scan times (~15min).