title: Interobserver and within-subject variances of T2-relaxation time and 1H-metabolite ratios in the normal hippocampus.
abstract: OBJECTIVE
  To investigate the magnetic resonance (MR) reproducibility of normal hippocampal volume (HV), temporal lobe volume (TLV), transversal relaxation time (T(2)) and (1)H-MR spectroscopy ((1)H-MRS) metabolite ratios.
  
  
  METHODS
  Two sets of HV, TLV, T(2) and MR spectroscopic metabolite signal ratios were determined in 27 healthy volunteers. HV and TLV were measured with a T(1)-weighted MR sequence; whereas T(2) measurements were performed with conventional spin-echo (CSE) and fast spin-echo (FSE) MR imaging sequences. The interobserver and within-subject variances of T(2) measurements were estimated.
  
  
  RESULTS
  Estimated right and left HV coefficients of variation (CV)=0.13. FSE T(2) measurements showed no significant differences in the interobserver (CV=0.02) and within-subject variances (CV=0.02). Measurements showed no differences in the interobserver (CV=0.02) and within-subject (CV=0.04) variances for the CSE T(2) of the right and left hippocampi. Metabolite ratios between N-acetyl aspartate (NAA) and creatine (Cr), choline (Cho) and creatine, and NAA and choline plus creatine (Cho + Cr) for the right hippocampus were 2.29+/-0.19, 1.52+/-0.14 and 0.91+/-0.05, respectively. Metabolite ratios for the left hippocampus were 2.18+/-0.10, 1.48+/-0.10 and 0.88+/-0.06, respectively.
  
  
  CONCLUSIONS
  HV, TLV, T(2) and (1)H MRS metabolite ratio measurements showed fair reproducibility with small CVs, and no differences in the interobserver and within-subject variances, including no differences between right and left TLV, and in the right and left T(2).
authors.affiliation: MR Research Center, Aarhus University Hospital, 8200 Aarhus, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Højrup
authors.forename: F T
authors.initials: FT
authors.lastname: Jensen
authors.forename: S
authors.initials: S
authors.lastname: Hokland
authors.forename: C
authors.initials: C
authors.lastname: Simonsen
authors.forename: T
authors.initials: T
authors.lastname: Christensen
authors.forename: J
authors.initials: J
authors.lastname: Frøkiaer
authors.forename: M
authors.initials: M
authors.lastname: Pedersen
mesh_terms: D000328:Adult; D005260:Female; D006624:Hippocampus / Q000033:anatomy & histology* / Q000378:metabolism*; D006801:Humans; D006859:Hydrogen / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009929:Organ Size; D012016:Reference Values; D013702:Temporal Lobe / Q000033:anatomy & histology
chemical_list: D006859:Hydrogen