In vivo proton magnetic resonance spectroscopy for metabolic changes of human brain edema

The metabolism of the brain was investigated in eight patients with peritumoral edema, six patients with ischemic stroke, and 28 normal controls using proton magnetic resonance (MR) spectroscopy. The MR studies were performed using a 1.5-T whole-body imaging and spectroscopy system with a 1500-msec repetition time (TR) and a 270-msec echo time (TE). The peak areas for N-acetyl-aspartate (NAA), choline-containing compounds (Cho), creatine and phosphocreatine (Cr), and lactate (Lac) were measured, and the NAA/Cr, Cho/Cr, and Lac/Cr ratios were calculated. To quantify and compare the serial spectra, relaxation effects were investigated by acquisitions at two different points (TRs or TEs) and by monoexponential fitting. The normal NAA/Cr and Cho/Cr ratios were 2.76 and 1.09, respectively. Lac could not be identified in normal brains. In ischemic stroke and peritumoral edema, significantly increased Lac/Cr and decreased NAA/Cr ratios were observed. Resolution of peritumoral edema was associated with normalized NAA/Cr ratio and disappearance of Lac. The T1 relaxation times of the metabolites were similar in normal brain and peritumoral edema, but the T2 values were significantly shortened. Serial measurements of T2 values in two patients with peritumoral edema showed gradual normalization corresponding to improvement of the edema. To absolutely quantify metabolite concentrations in edema, changes in relaxation times should be considered.