title: Effect of repetition time on metabolite quantification in the human brain in1H MR spectroscopy at 3 tesla.
abstract: To examine the effects of repetition time (TR) on metabolite concentration measurements in the human brain in1H magnetic resonance spectroscopy at 3 Tesla (T).
  
  
  
  Spectra were acquired from the posterior cingulate of five healthy adults at repetition times of 1.5 s, 3.0 s, 4.0 s, 6.0 s, and 8.0 s on a 3T MRI system. Relaxation data were also acquired for the water signal in the voxel of interest to separate tissue water and cerebrospinal fluid signal contributions. All data were quantified relative to total creatine and relative to the tissue water signal.
  
  
  
  On average, the variance for absolute metabolite concentrations was smaller than that of ratio concentrations (P = 0.003). Metabolite ratio concentrations calculated from a short TR of 1.5 s significantly differed (P < 0.05) from their "true" ratios, i.e., ratios corrected for T1-weighting. In comparison, absolute metabolite concentrations exhibited significant differences (P < 0.05) up to a 4-s TR.
  
  
  
  To minimize potential TR-dependent concentration differences at 3T, a minimum TR of 2.5 s is suggested for ratio concentration measurements, and a 5-s TR for absolute concentrations. When possible, preference should be to perform absolute concentration measurements.
  
  
  
  2 J. Magn. Reson. Imaging 2017;45:710-721.
authors.affiliation: Department of Radiology, Children's Healthcare of Atlanta, Atlanta, Georgia, USA.
authors.forename: Jack
authors.initials: J
authors.lastname: Knight-Scott
authors.affiliation: Department of Psychology, Emory University, Atlanta, Georgia, USA.
authors.forename: Patricia
authors.initials: P
authors.lastname: Brennan
authors.affiliation: Department of Radiology, Children's Healthcare of Atlanta, Atlanta, Georgia, USA.|Department of Radiology, Emory University, Atlanta, Georgia, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Palasis
authors.affiliation: MR R&D Collaborations, Siemens Healthcare, Atlanta, Georgia, USA.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhong
mesh_terms: D000328:Adult; D001921:Brain / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000378:metabolism*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D057054:Molecular Imaging / Q000379:methods*; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
keywords: H MRS; brain; metabolite T1; metabolite quantification; ultra-short TE