Simultaneous two-voxel localized 1 H-observed 13 C-edited spectroscopy for in vivo MRS on rat brain at 9.4 T: Application to the investigation of excitotoxic lesions Bich-Thuy Doan a,b, * , Gwennhael Autret a , Joël Mispelter c , Philippe Méric a , William Même d , Céline Montécot-Dubourg d , Jean-Loup Corrèze a , Frédéric Szeremeta b , Brigitte Gillet a , Jean-Claude Beloeil b a Laboratoire de RMN biologique, ICSN-CNRS, UPR, 2301, Avenue de la Terrasse, 91198 Gif sur Yvette cedex, France b Laboratoire d’IRM et SRM des milieux vivants, CBM, CNRS, UPR 4301, Rue Charles Sadron, 45071 Orléans, cedex, France c INSERM Unité 759, Institut Curie - recherche, Laboratoires R. Latarjet CU Bat 112, 91405 Orsay cedex, France d Université d’Orléans, Laboratoire de Neurobiologie, UPRES-EA 2633 BP 6759, 45 067 Orléans cedex, France article info Article history: Received 6 June 2008 Revised 21 January 2009 Available online 25 January 2009 Keywords: 1 H–( 13 C) localized MRS POCE-STEAM POCE-PRESS Hadamard encoding Cerebral energy metabolism [U– 13 C] glucose injection abstract 13 C spectroscopy combined with the injection of 13 C-labeled substrates is a powerful method for the study of brain metabolism in vivo. Since highly localized measurements are required in a heterogeneous organ such as the brain, it is of interest to augment the sensitivity of 13 C spectroscopy by proton acqui- sition. Furthermore, as focal cerebral lesions are often encountered in animal models of disorders in which the two brain hemispheres are compared, we wished to develop a bi-voxel localized sequence for the simultaneous bilateral investigation of rat brain metabolism, with no need for external additional references. Two sequences were developed at 9.4 T: a bi-voxel 1 H–( 13 C) STEAM-POCE (Proton Observed Carbon Edited) sequence and a bi-voxel 1 H–( 13 C) PRESS-POCE adiabatically decoupled sequence with Hadamard encoding. Hadamard encoding allows both voxels to be recorded simultaneously, with the same acquisi- tion time as that required for a single voxel. The method was validated in a biological investigation into the neuronal damage and the effect on the Tri Carboxylic Acid cycle in localized excitotoxic lesions. Fol- lowing an excitotoxic quinolinate-induced localized lesion in the rat cortex and the infusion of U– 13 C glu- cose, two 1 H–( 13 C) spectra of distinct (4  4  4 mm 3 ) voxels, one centred on the injured hemisphere and the other on the contralateral hemisphere, were recorded simultaneously. Two 1 H bi-voxel spectra were also recorded and showed a significant decrease in N-acetyl aspartate, and an accumulation of lactate in the ipsilateral hemisphere. The 1 H–( 13 C) spectra could be recorded dynamically as a function of time, and showed a fall in the glutamate/glutamine ratio and the presence of a stable glutamine pool, with a per- manent increase of lactate in the ipsilateral hemisphere. This bi-voxel 1 H–( 13 C) method can be used to investigate simultaneously both brain hemispheres, and to perform dynamic studies. We report here the neuronal damage and the effect on the Tri Carboxylic Acid cycle in localized excitotoxic lesions. Ó 2009 Published by Elsevier Inc. 1. Introduction In vivo 13 C NMR spectroscopy associated with the administra- tion of 13 C-labelled substrates is a powerful tool for the non-inva- sive investigation of brain metabolism. 13 C spectroscopy is the most appropriate method for monitoring the dynamics of metabo- lism in the Krebs cycle flux after the injection of substrates bearing labelled carbon atoms. In small animals, this method was first developed in 1985 with direct 13 C acquisition [1,2], and subse- quently with localization, with and without 1 H decoupling [3–5]. In 1992, the first chemical shift imaging (CSI) experiment on the rat brain was performed with direct detection of 13 C [6]. Despite yielding a well-resolved 13 C spectrum with good chem- ical shift dispersion, the low sensitivity of the 13 C nucleus and the need for highly localized measurements in a functionally heteroge- neous organ such as the brain have hampered the development of such methods, particularly for the study of small animals using small voxels localized on specific brain lesions. In addition to the development of high magnetic fields, a localized 13 C-edited se- quence with 1 H acquisition is therefore of great interest, as it would have the same sensitivity as a 1 H sequence. In 1990, a 1 H-detected 13 C spectroscopic study using the POCE sequence [5], allowed the transfer of 13 C between glucose and glutamate to be 1090-7807/$ - see front matter Ó 2009 Published by Elsevier Inc. doi:10.1016/j.jmr.2009.01.023 * Corresponding author. Present address: Laboratoire d’IRM et SRM du petit animal, CBM, CNRS, UPR 4301, Rue Charles Sadron, 45 071 Orléans Cedex, France. Fax: +33 2 38 63 15 17. E-mail address: doan@cnrs-orleans.fr (B.-T. Doan). Journal of Magnetic Resonance 198 (2009) 94–104 Contents lists available at ScienceDirect Journal of Magnetic Resonance journal homepage: www.elsevier.com/locate/jmr