ABSOLUTE METABOLITE QUANTIFICATION BY IN-VIVO NMR-SPECTROSCOPY - II -A MULTICENTER TRIAL OF PROTOCOLS FOR IN-VIVO LOCALIZED PROTON STUDIESOF HUMAN BRAIN

We have performed a multicentre trial to assess the performance of thr ee techniques for absolute quantification of cerebral metabolites usin g in vivo proton nuclear magnetic resonance (NMR). The techniques incl uded were 1) an internal water standard method, 2) an external standar d method based on phantom replacement, and 3) a more sophisticated met hod incorporating elements of both the internal and external standard approaches, together with compartmental analysis of brain water. Only the internal water standard technique could be readily implemented at all participating sites and gave acceptable precision and interlaborat ory reproducibility. This method was insensitive to many of the experi mental factors affecting the performance of the alternative techniques , including effects related to loading, standing waves and B-1 inhomog eneities; and practical issues of phantom positioning, user expertise and examination duration. However, the internal water standard method assumes a value for the concentration of NMR-visible water within the spectroscopic volume of interest. In general, it is necessary to modif y this assumed concentration on the basis of the grey matter, white ma tter and cerebrospinal fluid (CSF) content of the volume, and the NMR- visible water content of the grey and white matter fractions. Combinin g data from 11 sites, the concentrations of the principal NMR-visible metabolites in the brains of healthy subjects (age range 20-35 years) determined using the internal water standard method were (mean +/- SD) : [NAA] = 10.0 +/- 3.4 mM (n = 53), [tCho] = 1.9 +/- 1.0 mM (n = 51), [Cr + PCr] = 6.5 +/- 3.7 mM (n = 51). Evidence of system instability a nd other sources of error at some participating sites reinforces the n eed for rigorous quality assurance in quantitative spectroscopy. (C) 1 998 Elsevier Science Inc.