title: Longitudinal whole-brain N-acetylaspartate concentration in healthy adults.
abstract: OBJECTIVE
  Although NAA is often used as a marker of neural integrity and health in different neurologic disorders, the temporal behavior of WBNAA is not well characterized. Our goal therefore was to establish its normal variations in a cohort of healthy adults over typical clinical trial periods.
  
  
  METHODS
  Baseline amount of brain NAA, Q(NAA), was obtained with nonlocalizing proton MR spectroscopy from 9 subjects (7 women, 2 men; 31.2 ± 5.6 years old). Q(NAA) was converted into absolute millimole amount by using phantom-replacement. The WBNAA concentration was derived by dividing Q(NAA) with the brain parenchyma volume, V(B), segmented from MR imaging. Temporal variations were determined with 4 annual scans of each participant.
  
  
  RESULTS
  The distribution of WBNAA levels was not different among time points with respect to the mean, 12.1 ± 1.5 mmol/L (P > .6), nor was its intrasubject change (coefficient of variation = 8.6%) significant between any 2 scans (P > .5). There was a small (0.2 mL) but significant (P = .05) annual V(B) decline.
  
  
  CONCLUSIONS
  WBNAA is stable over a 3-year period in healthy adults. It qualifies therefore as a biomarker for global neuronal loss and dysfunction in diffuse neurologic disorders that may be well worth considering as a secondary outcome measure candidate for clinical trials.
authors.affiliation: Department of Radiology, New York University School of Medicine, New York, 10016, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Rigotti
authors.forename: I I
authors.initials: II
authors.lastname: Kirov
authors.forename: B
authors.initials: B
authors.lastname: Djavadi
authors.forename: N
authors.initials: N
authors.lastname: Perry
authors.forename: J S
authors.initials: JS
authors.lastname: Babb
authors.forename: O
authors.initials: O
authors.lastname: Gonen
mesh_terms: D000328:Adult; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000032:analysis; D001923:Brain Chemistry; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult
chemical_list: D001224:Aspartic Acid; C000179:N-acetylaspartate