title: Anterior to posterior hippocampal MRS metabolite difference is mainly a partial volume effect.
abstract: BACKGROUND
  The concentration of N-acetylaspartate (NAA) in hippocampus, as measured with magnetic resonance spectroscopy (MRS), and the ratio of NAA/(choline (Cho) + creatine (Cr)) are valuable tools in the lateralization of temporal lobe epilepsy (TLE). MRS of hippocampus is also increasingly used to study certain psychiatric and degenerative diseases. However, the reliability of such measurements of hippocampus has been questioned.
  
  
  OBJECTIVE
  To re-evaluate MRS imaging data from prior control subjects with regard to variation of metabolite concentrations in hippocampus from anterior to posterior and the partial volume (R)contribution to the measurements from adjacent tissue.
  
  
  METHODS
  Twelve healthy subjects, mean age 33 years, were studied with MRS imaging. The measurement volume was angled along the temporal horns and metabolite concentration images were reconstructed at the MR system. Regions of interest (ROIs) in the anterior, medial, and posterior parts of both hippocampi were evaluated. Signal normalization to the total MRS signal from all ROIs permitted pooling of individual data with different and unknown signal scaling. One subject was re-examined with a high resolution three-dimensional (3D) volume of the brain for evaluation of partial volumes in the MRS examination.
  
  
  RESULTS
  Overall, there were significantly lower concentrations of NAA in the anterior parts, and of (Cho+Cr) in the posterior parts, while the NAA/(Cho+Cr) ratio in the posterior parts of the mesial temporal lobes was significantly higher. Hippocampus accounted for one-half, one-third, and one-quarter of the anterior, middle, and posterior ROIs, respectively. The NAA/(Cho+Cr) ratio thus showed a reverse relationship to the relative volume of hippocampal tissue within the ROI.
  
  
  CONCLUSIONS
  Metabolite concentrations in the mesial temporal lobe obtained with MRS imaging represent the mean value of hippocampus and a considerable amount of adjacent tissue. To assess the hippocampus alone, an actual voxel well below 1 cm(3) and a sub-centimeter slice thickness are required.
authors.affiliation: Division of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Magnetkamera, Göteborg, Sweden. Goran.Starck@VGregion.se
authors.forename: Göran
authors.initials: G
authors.lastname: Starck
authors.forename: Barbro
authors.initials: B
authors.lastname: Vkhoff-Baaz
authors.forename: Maria
authors.initials: M
authors.lastname: Ljungberg
authors.forename: Kristina
authors.initials: K
authors.lastname: Malmgren
authors.forename: Eva
authors.initials: E
authors.lastname: Forssell-Aronsson
authors.forename: Lars
authors.initials: L
authors.lastname: Jönsson
authors.forename: Sven
authors.initials: S
authors.lastname: Ekholm
mesh_terms: D000328:Adult; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D002794:Choline / Q000378:metabolism; D003401:Creatine / Q000378:metabolism; D005260:Female; D006624:Hippocampus / Q000378:metabolism*; D006801:Humans; D021621:Imaging, Three-Dimensional; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013702:Temporal Lobe / Q000378:metabolism; D055815:Young Adult
chemical_list: D001224:Aspartic Acid; C000179:N-acetylaspartate; D003401:Creatine; D002794:Choline