Lateralisation with magnetic resonance spectroscopic imaging in temporal lobe epilepsy: an evaluation of visual and region-of-interest analysis of metabolite concentration images

We carried out spectroscopic imaging (MRSI) on nine consecutive patients wi th temporal lobe epilepsy being assessed for epilepsy surgery, and nine neu rologically healthy, age-matched volunteers. A volume of interest (VOI) was angled along the temporal horns on axial and sagittal images, and symmetri cally over the temporal lobes on coronal images. Images showing the concent rations of N-acetylaspartate (NAA) and of choline-containing compounds plus creatine and phosphocreatine (Cho + Cr) were used for lateralisation. We c ompared assessment by visual inspection and by signal analysis from regions of interest (ROI) in different positions, where side-to-side differences i n NAA/(Cho + Cr) ratio were used for lateralisation. The NAA/ (Cho + Cr) ra tio from the different ROI was also compared with that in the brain stem to assess if the latter could be used as an internal reference, e. g., for id entification of bilateral changes. The metabolite concentration images were found useful for lateralisation of temporal lobe abnormalities related to epilepsy. Visual analysis can, with high accuracy, be used routinely. ROI a nalysis is useful for quantifying changes, giving more quantitative informa tion about spatial distribution and the degree of signal loss. There was a large variation in NAA/ (Cho + Cr) values in both patients and volunteers. The brain stem may be used as a reference for identification of bilateral c hanges.