[Calculation of proton spectra of pure brain tissue types by multiple voxel measurements and image segmentation]

In localized in vivo proton NMR spectroscopy (1H MRS) of the human brain, it often cannot be avoided that the selected volume of interest (voxel) includes both gray matter (GM) and white matter (WM). Since the spectra of GM and WM differ, in general, the acquired spectrum represents a mixed spectrum that depends on the tissue composition inside the voxel. This study describes a method that enables the determination of pure GM spectra and pure WM spectra from mixed spectra. The pure tissue spectra are calculated from measured spectra acquired from several voxels with different mixed tissue compositions. For this purpose, the tissue composition in the voxels must be known. It is determined by segmentation of an additionally acquired 3D image data set with higher spatial resolution. In volunteer examinations, measurements were performed in different regions of the cerebrum, cerebellum, and thalamus. In all examined brain regions, particularly in the cerebellum, clear differences were found between the spectra of WM and GM. The detected differences in the spectra of WM and GM indicate that the tissue composition in the voxel has to be considered in patient studies, in order to distinguish pathological alterations in the spectra from the effects of tissue composition.