title: Implementation of two-dimensional L-COSY at 7 Tesla: an investigation of reproducibility in human brain.
abstract: OBJECTIVE
  To evaluate the utility of two-dimensional (2D) Localized Correlated Spectroscopy (L-COSY) in metabolic profiling of the human brain at 7 Tesla (T).
  
  
  METHODS
  The 2D L-COSY sequence was implemented at 7 T and its reliability was assessed by test-retest studies of a metabolite phantom and a healthy volunteer. L-COSY data were acquired from the occipital lobe of healthy subjects (n = 6; all male; age, 30-72 years) to assess intersubject variability. Additionally, two subjects underwent scans from the parieto-occipital region, basal ganglia, frontal lobe or dorsolateral prefrontal cortex to test the versatility of L-COSY in studying differing anatomy. Integral/volume measurements of L-COSY spectra were used to estimate normalized metabolite-to-creatine concentrations.
  
  
  RESULTS
  Phantom test-retest studies revealed coefficients of variation (CVs) of 3-20% for most metabolites. Human 2D L-COSY spectra permitted detection of several metabolite resonances from multiple locations and inter-subject variation studies demonstrated CVs of 4-26%. Cross-peaks from gamma-aminobutyric acid (GABA), isoleucine (Ile), lysine (Lys) and Ethanolamine (Eth) were quantified, which are not readily resolvable with conventional one-dimensional (1D) MR spectroscopy.
  
  
  CONCLUSIONS
  2D L-COSY at 7 T demonstrated improved sensitivity in detecting additional metabolites with reliability comparable to established techniques at lower fields, which may aid in the metabolic assessment of diseased states.
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Verma
authors.forename: Hari
authors.initials: H
authors.lastname: Hariharan
authors.forename: Rajakumar
authors.initials: R
authors.lastname: Nagarajan
authors.forename: Ravi P R
authors.initials: RP
authors.lastname: Nanga
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Delikatny
authors.forename: M
authors.initials: M
authors.lastname: Albert Thomas
authors.forename: Harish
authors.initials: H
authors.lastname: Poptani
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology* / Q000378:metabolism*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008875:Middle Aged; D057054:Molecular Imaging / Q000295:instrumentation / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
keywords: 7T; L-COSY; isoleucine; localized correlated spectroscopy; lysine; magnetic resonance spectroscopy