The goals of this research are to develop advanced magnetic resonance spectroscopy (MRS) and imaging techniques and to apply them and other complementary methods to studying brain metabolism, neurotransmission and enzyme activity. MRS allows measurement of neurotransmission of glutamate and GABA in vivo, which play important roles in many major psychiatric diseases including depression and schizophrenia. During 2011-2012, we have made significant progress in the development and applications of novel spectroscopic and imaging techniques for studying metabolism and neurotransmission in vivo in the brain. From our previous work, we have found that 13C labeling of glutamate and glutamine can be measured from human subjects by low power proton stochastic decoupling in the carboxylic/amide spectral region (Li, et al, NMR Biomed, 2010). We further extended this technique to simultaneous detection of the in vivo labeling kinetics of dual substrates and validated the isotopmer approach using rodents first (Y. Xiang, and J. Shen, Simultaneous detection of cerebral metabolism of different substrates by in vivo 13C isotopomer MRS, J. Neurosci. Methods., 198:815 (2011)). Then we applied this novel technique to human subjects (S. Li, Y. Zhang, M.F. Araneta, Y. Xiang, C. Johnson, R.B. Innis, and J. Shen, In vivo detection of 13C isotopomer turnover in the human brain by sequential infusion of 13C labeled substrates, J. Magn. Reson., 218:16-21 (2012)). Furher technical refinement of our stochastic decoupling method was made by developing a novel windowed decoupling method that allows for a 50% additional reduction in radiofrequency power deposition into the brain, making it feasible to perform 13C MRS at very high magnetic field strength (Y. Xiang, and J. Shen, Windowed stochastic proton decoupling for in vivo 13C magnetic resonance spectroscopy with reduced RF power deposition, J. Magn. Reson. Imaging, 34:968-972 (2011)). We overcame spectral overlapping between acetate and glutamate and between glutamine and aspartate in the carboxylic/amide spectral region by devisng a carbon-13 spectral editing technique (Y. Xiang, and J. Shen, Spectral editing for in vivo 13C magnetic resonance spectroscopy, J. Magn. Reson., 214:252-257 (2012)). For spectral overlapping in proton MRS we introduced the concept of spectral regularizaton into NMR (Y. Zhang, S. Li, S. Marenco, and J. Shen, Quantitative measurement of N-acetylaspartylglutamate (NAAG) at 3 Tesla using TE-averaged PRESS spectroscopy and regularized lineshape deconvolution, Magn. Reson. Med., 66:307-313 (2011)), which was further developed by incorporating soft constraints into spectral fitting (Y. Zhang, and J. Shen, Soft constraints in nonlinear spectral fitting with regularized lineshape deconvolution, Magn. Reson. Med., in press). In addition, collaborations with Dr. Zarate's group have led to the use of amino acid neurotransmitters as potential predictors of antidepressant response to ketamine (G. Salvadore, J.W. van der Veen, Y. Zhang, R. Machado-Vieira, J. Baumann, D.A. Luckenbaugh, J. Shen, W.C. Drevets, and C.A. Zarate, Jr., An investigation of amino acid neurotransmitters as potential predictors of antidepressant response to ketamine, Intl. J. Neuropsychopharmacology, 15:1063-72 (2012)). Collaborations with Dr. Warach's group help to shed light on the possible roles of glutathione in stroke (L. An, K.A. Dani, J. Shen, S.J. Warach, Pilot results of in vivo brain glutathione measurements in stroke patients, J. Cereb. Blood Flow Metab., in press.). Finally, we proposed and tested a novel method for accelerating magnetic resonance data acquisition based on partial derivatives of k space signals (J. Shen, Derivative encoding for parallel magnetic resonance imaging, Med. Phys., 38:5582-5589 (2011)). We plan to extend this method to spectroscopic imaging in the near future.
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