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Purpose/Introduction: For the absolute quantification1 of metabolites, appropriate T2 relaxation times must be used in the calculation. T2 relaxation times are usually specific to the sequence, tissue type, and region of interest in the human brain. Deelchand et al.2, reported T2 relaxation times of singlets at 9.4 T. In this work, T2 relaxation times of both singlets and J-coupled metabolites are reported for a GM rich voxel in the occipital region in the human brain at 9.4 T for the first time. The absolute concentrations mmolal (mmol/kg) of the metabolite peaks are also calculated. Subjects and Methods: A TE series of metabolite-cycled semi- LASER3 spectra were acquired on 11 healthy volunteers (TE:24, 32, 40, 52, 60 ms; TR: 6000 ms; NEX:96) with the transmit reference frequency set at 7.0 ppm and another spectra (TE/TR: 24/6000 ms, NEX:32) was acquired with the transmit reference frequency set at 2.4 ppm for absolute quantification. Tissue volume fractions were obtained from MP2RAGE image segmentation. Also, water reference spectra (NEX: 16) were acquired using semi-LASER sequence in order to avoid any influence of MC pulses. The raw data were pre-processed and were fit using LCModel-v6.3- 1L4. The concentrations were fit to a mono-exponential decay across the TE series in order to estimate the T2 relaxation times of the metabolite peaks. The concentrations of the metabolites were absolutely quantified using the formula given by Gasparovic et al.1 including correction factors. T1 and T2 relaxation times of water at 9.4 T were taken from Hagberg et al.5. T1 relaxation times of metabolites were considered from Wright et al.6, and T2 relaxation times calculated from this work were taken. The calculated T2 relaxation times for the summed spectra from 11 healthy volunteers and the mean from T2 values for individual spectra with standard deviations are reported in Table 1, which are overall in a good agreement. All reported T2 relaxation times show the expected negative correlation with increasing the field strength7,8. Absolute concentrations in mmolal with and without T2 correction are shown in Table 2 for a fair comparison between this work and other studies2,9 which do not include T2 correction. The values with T2 correction also agree with Marjanska et al.,8 except for minor discrepancies which could be from small deviations in the calculation of T2 values.
