Voxel placement and data quality.

<p>(A) Images of human brains illustrating the position and size of the VOI. (B) Representative ¹H STEAM spectra (4 T, 27 mL, <i>T</i>_R = 4.5 s, number of averages = 4) measured at seven <i>T</i>_Es from the human occipital lobe in one young (left) and one elderly (right) subject. The vertical scale has been adjusted such that the NAA resonance detected at <i>T</i>_E = 10 ms for both young and elderly subjects has the same intensity. Horizontal dashed lines are visual guides to indicate that the intensity of NAA and tCr signals decrease faster in the elderly than the young subject. The faster signal decay reflects a shorter <i>T</i>₂ value. Spectra are shown without line broadening. NAA, N-acetylaspartate, tCr, total creatine = creatine (Cr) + phosphocreatine (PCr), tCho, total choline = choline containing compounds.</p

<i>T</i>₂ fits for metabolites in young and elderly subjects.

<p>Individual exponential fits (represented by decaying lines) of the experimentally measured data for (A) the NAA singlet at 2.01 ppm, (B) the tCr signal at 3.03 ppm, and (C) the tCho singlet at 3.2 ppm in one representative young and one representative elderly subject. The amplitude of all data sets was normalized by setting the first <i>T</i>_E point to unity for both young and elderly subjects. For all metabolites and all subjects, <i>T</i>₂s were fit with R² ≥ 0.918, with the lowest R² for tCho.</p