Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disorder mainly involving the upper and lower motor neurons. Previous studies showed that biochemical changes in ALS detected by MR spectroscopy were important in the pathogenesis ¹ and helpful in detecting pathology in early stage of disease ². The purpose of this study was to quantify brain metabolites in ALS patients using ultra-high (7-Tesla) MR spectroscopy and investigate how these metabolites correlate with clinical outcomes.The study was approved by the Institutional Review Board and written informed consent was obtained from all subjects recruited in this study. In total 12 patients with ALS and 12 healthy age-matched individuals were recruited. Subjects were required to have a vital capacity (VC) ≥ 50% at screening. Other clinical outcomes such as disease duration, revised ALS Functional Rating Scale (ALSFRS-R), and reflex testing evaluating upper motor neuron dysfunction were also obtained. In vivo MR spectroscopy was performed on a 7T MR scanner (Siemens Healthcare, GmbH, Erlangen, Germany) with a 32-channel receive coil. MR sequences included a multi-echo MPRAGE (MEMPRAGE) sequence ³ with 1mm³ isotropic resolution for spectrum localization and gray matter/white matter/cerebrospinal fluid (CSF) segmentation and a single voxel 1H MR spectra from the left motor cortex (VOI = 2 x 2 x 2 cm³) using an ultra short echo time (5ms) MRS (stimulated echo acquisition model, STEAM) with VAPOR (Variable Power RF pulses and Optimized Relaxation Delays) water suppression. Water unsuppressed spectra were also acquired to estimate absolute concentrations in institutional units (I.U). LCModel was employed to quantify brain metabolites using a basis set with 17 metabolites ⁴. Metabolite concentrations were evaluable for further statistical analysis for metabolites of which their Cramer-Rao lower bounds were less than 20% including gamma-Aminobutyric Acid (GABA), Glutamine (Gln), Glutamate (Glu), Glutathione (GSH), myo-Inositol (mI), N-acetylaspartate (NAA), Nacetylaspartylglutamate (NAAG), Taurine (Tau), Creatine+Phosphocreatine (tCr), and Choline-containing compounds (Phosphorylcholine (PCh) and Glycerophosphorylcholine (GPC), tCho). The MEMPRAGE sequence was used to segment brain volume of white matter, gray matter, or CSF within the 2x2x2cm3 MRS voxel using FMRIB Software Library (FSL 5.0) (Oxford, UK). All metabolite levels were adjusted for CSF contribution. Student t tests were used to compare age and metabolite concentrations between ALS subjects and healthy controls. Spearman correlation coefficients were calculated to estimate the correlations between brain metabolite concentrations and clinical outcomes. All analyses were conducted using JMP 11.0 (SAS, Cary, NC).The absolute and relative concentrations of brain metabolites in the left motor cortex are shown in table 1. In ALS, there were significantly decreased metabolites of NAA (P=0.006), NAA+NAAG (P=0.008), and Glu (P=0.03) as well as a trend towards reduced GABA (P=0.059). For the relative concentration (/tCr), there were only 2 trends towards significant reduction in the metabolites of NAA (P=0.07) and NAA+NAAG (P=0.06) in ALS patients compared to healthy controls. Correlations between brain metabolite levels in the left motor cortex and clinical outcomes including ALSFRS-R, VC, and reflex are shown in table 2 and figures 1-3.Our study demonstrates that patients with ALS have significantly decreased NAA, Glu and GABA in the left motor cortex consistent with neuronal injury or loss. The decrease in Glu is likely driven by the loss of intracellular Glu due to neuronal degeneration; the decrease in GABA suggests a reduction in inhibitory transmission. Neuronal injury/loss (measured by decreased NAA/Cr) and elevated levels of oxidative stress (measured by a decrease in GSH/Cr) correlated with a decrease in ALSFRS-R suggesting that both metabolites are clinically relevant. Lower vital capacity was also associated with decreases in NAA, Glu and Cr, markers of neuronal integrity and energy metabolism. Furthermore, increased pathological reflexes, a clinical marker of upper motor neuron degeneration correlated positively with mI and Cho, both markers of glial activation / inflammation and negatively with NAA/Cr. 7T MR spectroscopy may contribute at improving the understanding of ALS disease mechanisms and provide effective biomarkers of disease correlating well with ALS clinical outcomes.