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Purpose Carbon-13 (13C) MR spectroscopy (MRS) of the human brain at 7 Tesla (T) may pose patient safety issues due to high radiofrequency (RF) power deposition for proton decoupling. The purpose of present work is to study the feasibility of in vivo 13C MRS of human brain at 7 T using broadband low RF power proton decoupling. Methods Carboxylic/amide 13C MRS of human brain by broadband stochastic proton decoupling was demonstrated on a 7 T scanner. RF safety was evaluated using the finite-difference time-domain method. 13C signal enhancement by nuclear Overhauser effect (NOE) and proton decoupling was evaluated in both phantoms and in vivo. Results At 7 T, the peak amplitude of carboxylic/amide 13C signals was increased by a factor of greater than 4 due to the combined effects of NOE and proton decoupling. The 7 T 13C MRS technique used decoupling power and average transmit power of less than 35 watts (W) and 3.6 W, respectively. Conclusion In vivo 13C MRS studies of human brain can be performed at 7 T, well below the RF safety threshold, by detecting carboxylic/amide carbons with broadband stochastic proton decoupling. Magn Reson Med 75:954-961, 2016. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

When volume coils are used for 1H imaging of the human head at 7T, wavelength effects in tissue cause a variation in intensity, that is typically brighter at the center of the head and darker in the periphery. Much of this image nonuniformity can be attributed to variation in the effective transmit B1 field, which falls by ∼ 50% to the left and right of center at mid-elevation in the brain. Because most of this B1 loss occurs in the periphery of the brain, we have explored use of actively controlled, off-resonant loop elements to locally enhance the transmit B1 field in these regions. When tuned to frequencies above the NMR frequency, these elements provide strong local enhancement of the B1 field of the transmit coil. Because they are tuned off-resonance, some volume coil detuning results, but resistive loading of the coil mode remains dominated by the sample. By digitally controlling their frequency offsets, the field enhancement of each inner element can be placed under active control. Using an array of eight digitally controlled elements placed around a custom-built head phantom, we demonstrate the feasibility of improving the B1 homogeneity of a transmit/receive volume coil without the need for multiple radio frequency transmit channels. Magn Reson Med, 2011. © 2011 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

This study presents the detection of [2-13C]glucose metabolism in the carboxylic/amide region in the human brain, and demonstrates that the cerebral metabolism of [2-13C]glucose can be studied in human subjects in the presence of severe hardware constraints of widely available 3 T clinical scanners and with low-power stochastic decoupling. In the carboxylic/amide region of human brain, the primary products of 13C label incorporation from [2-13C]glucose into glutamate, glutamine, aspartate, γ-aminobutyric acid, and N-acetylaspartate were detected. Unlike the commonly used alkanyl region where lipid signals spread over a broad frequency range, the carboxylic carbon signal of lipids was found to be confined to a narrow range centered at 172.5 ppm and present no spectral interference in the absence of lipid suppression. Comparison using phantoms shows that stochastic decoupling is far superior to the commonly used WALTZ sequence at very low decoupling power at 3 T. It was found that glutamine C1 and C5 can be decoupled using stochastic decoupling at 2.2 W, although glutamine protons span a frequency range of ≈700 Hz. Detailed specific absorption rate analysis was also performed using finite difference time domain numerical simulation. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

When volume coils are used for (1)H imaging of the human head at 7 T, wavelength effects in tissue cause a variation in intensity, that is typically brighter at the center of the head and darker in the periphery. Much of this image nonuniformity can be attributed to variation in the effective transmit B(1) field, which falls by ∼ 50% to the left and right of center at mid-elevation in the brain. Because most of this B(1) loss occurs in the periphery of the brain, we have explored use of actively controlled, off-resonant loop elements to locally enhance the transmit B(1) field in these regions. When tuned to frequencies above the NMR frequency, these elements provide strong local enhancement of the B(1) field of the transmit coil. Because they are tuned off-resonance, some volume coil detuning results, but resistive loading of the coil mode remains dominated by the sample. By digitally controlling their frequency offsets, the field enhancement of each inner element can be placed under active control. Using an array of eight digitally controlled elements placed around a custom-built head phantom, we demonstrate the feasibility of improving the B(1) homogeneity of a transmit/receive volume coil without the need for multiple radio frequency transmit channels., (Copyright © 2011 Wiley-Liss, Inc.)