title: Low-grade glioma: correlation of short echo time 1H-MR spectroscopy with 23Na MR imaging.
abstract: OBJECTIVE
  There is considerable variability in the clinical behavior and treatment response of low-grade (WHO grade II) gliomas. The purpose of this work was to characterize the metabolic profile of low-grade gliomas by using short echo time (1)H-MR spectroscopy and to correlate metabolite levels with MR imaging-measured sodium ((23)Na) signal intensity. Based on previous studies, we hypothesized decreased N-acetylaspartate (NAA) and increased myo-inositol (mIns), choline (Cho), glutamate (Glu), and (23)Na signal intensity in glioma tissue.
  
  
  METHODS
  Institutional ethics committee approval and informed consent were obtained for all of the subjects. Proton ((1)H-MR) spectroscopy (TR/TE = 2200/46 ms) and sodium ((23)Na) MR imaging were performed at 4T in 13 subjects (6 women and 7 men; mean age, 44 years) with suspected low-grade glioma. Absolute metabolite levels were quantified, and relative (23)Na levels were measured in low-grade glioma and compared with the contralateral side in the same patients. Two-sided Student t tests were used to test for statistical significance.
  
  
  RESULTS
  Significant decreases were observed for NAA (P < .001) and Glu (P = .004), and increases were observed for mIns (P = .003), Cho (P = .025), and sodium signal intensity (P < .001) in low-grade glioma tissue. Significant correlations (r(2) > 0.25) were observed between NAA and Glu (P < .05) and between NAA and mIns (P < .01). Significant correlations were also observed between (23)Na signal intensity and NAA (P < .01) and between (23)Na signal intensity and Glu (P < .01). Ratios of NAA/mIns, NAA/(23)Na, and NAA/Cho were altered in glioma tissue (P < .001); however based on the t statistic, NAA/(23)Na (t = 9.6) was the most significant, followed by NAA/mIns (t = 6.1), and NAA/Cho (t = 5.0).
  
  
  CONCLUSIONS
  Although Glu concentration is reduced and mIns concentration is elevated in low-grade glioma tissue, the NAA/(23)Na ratio was the most sensitive indicator of pathologic tissue.
authors.affiliation: Laboratory for Functional Magnetic Resonance Research, Robarts Research Institute, London, Ontario, Canada. rob.bartha@imaging.robarts.ca
authors.forename: R
authors.initials: R
authors.lastname: Bartha
authors.forename: J F
authors.initials: JF
authors.lastname: Megyesi
authors.forename: C J
authors.initials: CJ
authors.lastname: Watling
mesh_terms: D000328:Adult; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000032:analysis; D001921:Brain / Q000378:metabolism / Q000473:pathology; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000378:metabolism*; D005260:Female; D005910:Glioma / Q000175:diagnosis* / Q000378:metabolism*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D011522:Protons; D012964:Sodium / Q000032:analysis*; D012975:Sodium Isotopes; D013223:Statistics as Topic
chemical_list: D011522:Protons; D012975:Sodium Isotopes; D001224:Aspartic Acid; C000179:N-acetylaspartate; D012964:Sodium