Quantitative in vivo1H-spectroscopy of healthy and tumorous human brain tissue at 4 tesla

In 35 healthy volunteers 79 hydrogen spectra were measured from the parietal lobe, parieto-occipital lobe, frontal lobe, temporal lobe, thalamus and insular region. Voxels were selected with a double spin-echo sequence at TE 71, 135 and 270 ms. The spectra were quantitatively evaluated by fitting a Lorentzian model to the resonances of the creatine pool at 3.02 ppm and the choline pool at 3.22 ppm. No differences were found in the intensities of either metabolite in the 6 investigated regions. Creatine and choline were equally distributed in these regions. The interindividual reproducibility of the spectra decreases with longer echo delays. The coefficients of variation of the areas of creatine and choline corrected for the number of acquisitions and the voxel size are ±13% at TE 71 ms, ±23% at TE 135 ms, ±43% at TE 270 ms. This is caused by an interindividual variation in T₂ by ±15%, which affects all resonances of a spectrum. Signal variations from the fit, the Q-factor of the RF-coil loaded with different subjects and variations in the flip angle are less than 10% at each echo delay. The intraindividual variation without repositioning of the subject was better than 10%. Using creatine as an internal reference the ratios of the amplitudes of N-acetyl-aspartate (NAA) at 2.01 ppm and γ-methylene protons of glutamic acid at 2.34 ppm were not specific for special regions of the brain. Only in the temporal lobe the ratio of NAA and creatine was reduced. A mean concentration ratio of 1.7 for NAA and Cre was measured as an average over all subjects and the investigated brain regions with the exception of the temporal lobe. Initial applications of the method to 7 patients with brain tumors are described.