© Pol J Radiol, 2010; 75(2): 22-26 Krukowski P et al – Analysis of the brain proton magnetic resonance… decreased with age, and with neurodegenerative processes, as well as with (among others) brain tissue injuries caused by proliferative, inflammatory, and vascular processes, past trauma or, potentially also, chemotherapy or radio- therapy, and with a toxic brain injury (e.g. carbon monox- ide poisoning). The increase in the NAA level in the brain is much more seldom and can be found in i.a. Canavan disease (spongiform leukodystrophy) and, physiologically, during the myelinisation processes in the early years of life [1,5]. A band of creatine and phosphocreatine (Cr) is observed at 3.03 ppm. Due to its relative stability of concentration and signal intensity in the brain, creatine is used as an ‘internal standard’ – to calculate its ratios to other metabolites [1]. In cells, it acts as a ‘quickly available energy source’ [1], which can be confirmed by a fact of its higher concentra- tion in the grey matter (found by us). Changes in the brain levels of creatine are connected with a significant injury of the white and the grey matter (e.g. as a result of chemo- therapy or radiotherapy, or a strong injury). Choline (Cho) band is present at 3.20 ppm. In brain cells, choline is i.a. a precursor of phosphatydylocholine and a marker of cell membrane integrity, and thus its concentra- tion is higher in the white matter of the brain. Choline is also an indicator of the myelin sheath breakdown – its level increases in demyelination diseases (e.g. multiple sclerosis) [1,5]. Its increase is typical for proliferative processes, and is accompanied by a decreased NAA level. Cho increase is also observed in posttraumatic brain injuries (e.g. in axonal injury) [5]. Myoinositol (mI) band is found at 3.56 ppm. According to the majority of the literature sources, myoinositol is present in astrocytes only – its levels increase in astrocyte prolifera- tion [1]. Increase in mI signal intensity is also observed in dementive diseases (e.g. Alzheimer’s disease) [5]. Literature describing differences between the white and the grey matter bases on the measurements of absolute metabolite concentrations mainly. Schuff et al. [1] found a higher NAA and Cho concentration within the white matter, and a higher Cr concentration in the grey matter. Noworolski et al. [6] also revealed a higher Cr concentra- tion in the grey matter and Cho in the white matter, with (as the authors of this study) a higher NAA level in the grey matter (data acquisition was carried out in the white mat- ter of the fornix and the occipital grey matter). Noworolski et al examined also the proportions of metabolites: in the grey matter, higher NAA/Cho, NAA/Cr and Cr/Cho values were found than in the white matter, with the data acquisi- tion carried out in the white matter of the fornix and in the occipital grey matter. In the study by Angelie et al. [2], a higher value of the Cho/Cr proportion was found within the white matter, similarly to our results. In our study, we based on the evaluation of metabolite pro- portions. As Noworolski et al. [6], we found similar propor- tions in Cho/Cr and Cho/NAA but higher values of NAA/Cr proportions in the white matter compared to the grey mat- ter, than the above mentioned authors. When trying to explain contrary results on NAA values, obtained by Schuff et al. [1] and by Noworolski et al. [6], we concluded that such discrepances may follow from the difference in sig- nal intensity of Cr rather than NAA. In both cases, our data correlate with the results of studies showing a higher NAA and Cr concentration in the grey matter. At the same time, values of the PWM/PGM proportion suggest a higher sig- nal intensity of NAA, Cr and mI in the grey matter, and of Cho in the white matter. Similar conclusions can be drawn on the basis of values of the%Met proportion, which were significantly different for the grey and for the white mat- ter. It should be added that when analysing data for choline concentration in the grey matter, we evaluated in our study only the grey matter of the occipital lobe, where, according to the analysis by Pouwels et al. [7], Cho concentration is two times lower than in the frontal lobes. When carrying out a spectroscopic evaluation of a voxel located in the grey matter, we should take into consider- ation a potential influence of fluid spaces and signal inten- sity of water included in the cerebrospinal fluid (CSF), increasing with patient’s age. The age factor and its influ- ence on the water signal increase was confirmed by Brooks et al. in a comparatively located voxel [8]. The PGM voxel was located in the grey matter of both posterior cingulate gyra, including the longitudinal fissure of the brain. The influence of water on signal intensity may be eliminated within the grey matter with the use of proportions includ- ing metabolites other than water. At the same time, we believe that the increase in CSF signal intensity does not have any influence on signal disturbance in the PWM voxel – i.e. voxel not containing fluid spaces. This opinion was confirmed with studies conducted by Brooks et al. [8], who did not reveal age-dependent changes in the rate of water included in the nervous tissue of the brain. Therefore, in our opinion, although the proportions including water should be approached with reserve in PGM, they are reli- able for PWM. Significant differences in the signals of metabolites and their proportions, showed in our study, require spectro- scopic evaluation of potential pathologies in comparison to either PWM or PGM, depending on lesion location. Conclusions The obtained results showed a higher NAA, Cr and mI con- centration in the grey matter and Cho in the white matter, which is expressed by higher values of Cho/Cr and Cho/NAA proportions in the white matter. NAA/Cr values higher in PWM than in PGM may be influenced by the level of the Cr signal rather than of the NAA signal, which correlates also with the results showing higher NAA and Cr concen- trations in PGM. A higher NAA concentration in the grey matter confirms the literature data, according to which this metabolite functions as a neuronal marker. A strong cre- atine signal intensity in the grey matter may be explained (most probably) by an intensive metabolism of this com- pound, while a strong signal of choline in the white matter results from the role of this compound – being a component of myelin sheaths. 25