Original Article © Pol J Radiol, 2010; 75(2): 22-26 Table 1. The comparison of the grey and of the white matter – Student’s t-test, mean values of metabolite proportions, N=90. Table 2. The comparison of the intensity of metabolite signals in PGM and PWM voxels, N=90. 1610.368 2159.436 Table 3. Comparison of %Met values between the grey and the white matter. All differences are statistically significant, Student’s t-test, p<0.01, N=90. PGM 1.637 0.562 0.570 0.345 1.024 0.350 0.0010224 0.0006251 0.0003509 0.000356 PWM 1.847 0.997 0.658 0.543 0.666 0.358 0.0008726 0.0004746 0.0004702 0.000311 NAA/Cr* Cho/Cr* mI/Cr* Cho/NAA* mI/Cho* mI/NAA H2O/Cr* NAA/H2O* Cr/H2O* Cho/H2O* mI/H2O* * Statistically significant differences, p<0.01. the differences in the spectroscopic image of the grey and the white matter, we introduced (apart from proportions using creatine or water as an internal standard) some additional proportions of NAA, Cr, Cho and mI signals in PGM to signals in PWM (e.g. NAAPGM/NAAPWM). In case of NAA, Cr, Cho and mI, we calculated also the ratio of the analysed metabolite signal (%Met) to the sum of signals of all the remaining metabolites in a given voxel – e.g.% NAAPGM=NAAPGM/(NAAPGM+CrPGM+ChoPGM+mIPGM). The obtained values were compared for the grey and for the white matter. To calculate mean values, we applied a student’s t-test and Mann-Whitney U test. To assess the correlation between the changes in the proportions and the age, we applied the Pearson and Spearman coefficient. Results We found statistically significantly higher values of the NAA/Cr, Cho/Cr, mI/Cr, Cho/NAA, and Cho/H2O proportions within the white matter than within the grey matter. In the grey matter, the following proportions were significantly higher than in the white matter: mI/Cho, NAA/H2O, Cr/H2O and mI/H2O. The mI/NAA proportion revealed a higher mean value in PWM, which, however, was not statistically significant (Table 1). When comparing the proportions of individual metabolites in the voxels, the following values were found: NAAPGM/NAAPWM=1.055; CrPGM/CrPWM=1.19; ChoPGM/ChoPWM=0.67; MiPGM/mIPWM=1.04 (Table 2). No correlation was found between the NAAPGM/NAAPWM, CrPGM/CrPWM, ChoPGM/ChoPWM, and mIPGM/mIPWM propor- tions and the age of the examined patients. When evaluating %Met values within PGM and PWM, we found statistically significant differences between the white and the grey matter: for %NAA, %Cr and %mI, a higher value was found in PGM, while for %Cho, a higher percentage was noted within PWM (Table 3). 24 Mean 1.055495 1.189104 0.674067 1.039426 %MetPGM 0.434011 0.265717 0.149096 0.151176 Standard deviation 0.131290 0.144824 0.101038 0.168765 %MetPWM 0.410118 0.222786 0.221055 0.146040 NAAPGM/PWM CrPGM/PWM ChoPGM/PWM mIPGM/PWM Metabolite NAA Cr Cho mI Discussion The study was conducted prospectively. From among 194 patients who underwent spectroscopic brain examination, we excluded individuals suspected for dementive, vascular, demyelinisation, proliferative and inflammatory lesions, as well as patients with lesions found on basic MR imag- ing (100 persons in total). Other exclusion criteria involved artifacts in HMRS images (4 cases). Finally, 90 individuals (aged 8–80 years) were included in the study group. The HMRS examination may be performed (as in the case of this study) using a single voxel method (SVS) or chemi- cal shift imaging (CSI), i.e. multi-voxel spectroscopy (MVS) in other words. The CSI method is especially useful in case of evaluation of larger pathological lesions, as it allows for selection of a specific plane of brain section and its divi- sion into voxels, owing to which it is possible to evaluate potential changes in the spectroscopic spectrum in a spe- cific, larger area. However, the examination lasts longer, and the applied parameters hinder the evaluation of the amplitudes of metabolites with shorter relaxation times [1]. The SVS method allows for a quick assessment of a wide range of metabolites in a specific, reproducible site of brain, in which a single voxel will be placed. In the pre- sented study group, voxels were located both in the white, and in the grey matter, due to the presence of differenc- es between their spectroscopic spectrum, reported by the literature [2,3]. Currently, for SVS evaluation, most of the centres apply the PRESS sequence, which, in comparison to the STEAM sequence, results in a nearly twofold higher signal to noise ratio (SNR) [3]. Thanks to the application of a double spin echo (two RF impulses 180°), this sequence is also less prone to disturbances caused by blood flow and brain motion [4]. A maximal NAA signal intensity is observed at ppm of 2.02. NAA is defined as a marker of neurons - its signal intensity