Background: Post processing for brain spectra has a great influence on the fit quality of individual spectra, as well\nas on the reproducibility of results from comparable spectra. This investigation used pairs of spectra, identical in\nsystem parameters, position and time assumed to differ only in noise. The metabolite amplitudes of fitted time\ndomain spectroscopic data were tested on reproducibility for the main brain metabolites.\nMethods: Proton spectra of white matter brain tissue were acquired with a short spin echo time of 30 ms and a\nmoderate repetition time of 1500 ms at 1.5 T. The pairs were investigated with one time domain post-processing\nalgorithm using different parameters. The number of metabolites, the use of prior knowledge, base line parameters\nand common or individual damping were varied to evaluate the best reproducibility.\nResults: The protocols with most reproducible amplitudes for N-acetylaspartate, creatine, choline, myo-inositol and\nthe combined Glx line of glutamate and glutamine in lesion free white matter have the following common\nfeatures: common damping of the main metabolites, a baseline using only the points of the first 10 ms, no\nadditional lipid/macromolecule lines and Glx is taken as the sum of separately fitted glutamate and glutamine. This\nparameter set is different to the one delivering the best individual fit results.\nDiscussion: All spectra were acquired in ââ?¬Å?lesion freeââ?¬Â (no lesion signs found in MR imaging) white matter. Spectra\nof brain lesions, for example tumors, can be drastically different. Thus the results are limited to lesion free brain\ntissue. Nevertheless the application to studies is broad, because small alterations in brain biochemistry of lesion free\nareas had been detected nearby tumors, in patients with multiple sclerosis, drug abuse or psychiatric disorders.\nConclusion: Main metabolite amplitudes inside healthy brain can be quantified with a normalized root mean\nsquare deviation around 5 % using CH3 of creatine as reference. Only the reproducibility of myo-inositol is roughly\ntwice as bad. The reproducibility should be similar using other references like internal or external water for an\nabsolute concentration evaluation and are not influenced by relaxation corrections with literature values.
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