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One of the challenges of optimizing signal-to-noise ratio (SNR) and image quality in 13C metabolic imaging using hyperpolarized 13C-pyruvate is associated with the different MR signal time-courses for pyruvate and its metabolic products, lactate and alanine. The impact of the acquisition time window, variation of flip angles, and order of phase encoding on SNR and image quality were evaluated in mathematical simulations and rat experiments, based on multishot fast chemical shift imaging (CSI) and three-dimensional echo-planar spectroscopic imaging (3DEPSI) sequences. The image timing was set to coincide with the peak production of lactate. The strategy of combining variable flip angles and centric phase encoding (cPE) improved image quality while retaining good SNR. In addition, two aspects of EPSI sampling strategies were explored: waveform design (flyback vs. symmetric EPSI) and spectral bandwidth (BW = 500 Hz vs. 267 Hz). Both symmetric EPSI and reduced BW trended toward increased SNR. The imaging strategies reported here can serve as guidance to other multishot spectroscopic imaging protocols for 13C metabolic imaging applications. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

We present for the first time dynamic spectra and spectroscopic images acquired in normal rats at 3T following the injection of 13C-1-pyruvate that was hyperpolarized by the dynamic nuclear polarization (DNP) method. Spectroscopic sampling was optimized for signal-to-noise ratio (SNR) and for spectral resolution of 13C-1-pyruvate and its metabolic products 13C-1-alanine, 13C-1-lactate, and 13C-bicarbonate. Dynamic spectra in rats were collected with a temporal resolution of 3 s from a 90-mm axial slab using a dual 1H-13C quadrature birdcage coil to observe the combined effects of metabolism, flow, and T1 relaxation. In separate experiments, spectroscopic imaging data were obtained during a 17-s acquisition of a 20-mm axial slice centered on the rat kidney region to provide information on the spatial distribution of the metabolites. Conversion of pyruvate to lactate, alanine, and bicarbonate occurred within a minute of injection. Alanine was observed primarily in skeletal muscle and liver, while pyruvate, lactate, and bicarbonate concentrations were relatively high in the vasculature and kidneys. In contrast to earlier work at 1.5T, bicarbonate was routinely observed in skeletal muscle as well as the kidney and vasculature. Magn Reson Med 58:65-69, 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]