D'Souza, Patricia Christina; (1997) Quantitation of brain metabolite concentrations and temperature by proton magnetic resonance spectroscopy. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Analysis of in vivo proton magnetic resonance spectroscopy (1H MRS) data is complicated by overlapping resonances and phase modulated multiplets. A linear combination of in vitro model metabolite spectra (LCM), used to analyse an in vivo spectrum, resolves closely overlapping resonances by the fitting of non overlapping resonances from the same metabolites. Also in vitro phase modulation effects and lineshape characteristics reflect those in vivo because the model spectra are acquired using exactly the same data acquisition as in vivo. Basis sets of PRESS voxel localisation and surface coil model spectra (acquired at the 2.4 T and 7 T field strengths respectively) were constructed using the major 1H MRS detectable brain metabolites: alanine; aspartate; β-hydroxybutyrate; choline containing compounds (Cho); creatine plus phosphocreatine (Cr); γ-aminobutyrate; glutamine; glutamate; glycine; lactate (Lac); myo-inositol; N-acetyl-aspartate (NAA); N-acetyl-aspartate-glutamate; scyllo-inositol; and taurine. Brain spectra from newborn infants were analysed using the PRESS basis sets and LCM. The results were compared with those found from Lorentzian frequency domain fitting. LCM analysis improved estimates particularly of Lac and NAA levels and also their T2 relaxation. LCM was also applied to the analysis of (surface coil) spectra from studies of cerebral hypoxia-ischaemia in the newborn piglet. LCM determined changes in all the metabolites in the basis set, rather than only a few as by Lorentzian fitting. Changes in relative metabolite concentrations reproduced in the newborn piglet resembled those seen in birth-asphyxiated human infants. Results showed that hypothermia was cerebroprotective whereas intravenous magnesium was not. Local brain temperature was estimated by in vivo 1H MRS. Relative to the Cho, Cr or NAA singlet resonances, the chemical shift of water measured from surface coil piglet brain spectra depended linearly on temperature from 30 - 40 °C. Thalamic and occipito-parietal temperatures in human infants were estimated with adequate sensitivity (± 0.6 °C).

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