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Abstract

Purpose/Introduction: 31P spectroscopy in the brain has enormous potential in medical and neuroscientific examinations, but suffers from low SNR and correspondingly limited spatial resolution. Using ultra-high field strengths not only improves the intrinsic SNR of the measurements, but, in contrast to most other nuclei, also leads to shorter T1 values [1] and thus allows for further improvement of the spectral quality. In this study, we have measured the T1 in the human visual cortex at a field strength of 9.4 T. Subjects and Methods: The spectra were acquired on a 9.4 T whole body human MR Scanner, using a home-built 27 channel 31P coil with a 1H channel for localization and shimming [2]. T1 was determined with an inversion-recovery sequence, using a 15 ms TR-FOCI pulse for inversion followed by a 0.30 ms excitation pulse. Five healthy volunteers were scanned with TR = 15,000 ms, bandwidth 5000 Hz and 20–60 averages. Spectra with 7–8 inversion times between 61 ms and 14,000 ms were acquired. Only signals from the two coil elements below the visual cortex were used for quantification, a total of eight saturation pulses served to further suppress signal from outside the visual cortex. Peak amplitudes were determined with the AMARES-routine in jMRUI (v5.2) and a monoexponential relaxation curve was fit to the data using MATLAB (R2016a). Results: Figure 1 shows a typical 31P spectrum acquired from the human visual cortex at 9.4T. 12 resonances could be quantified in all subjects. The measured T1-values are listed in Table 1 and plotted in a comparison to previously published 7T data [3] in Fig. 2. Discussion/Conclusion: Previous studies have shown a decrease of the T1 of phosphorus metabolites with increasing magnetic field due to a strong chemical shift anisotropy effect. Our results confirm those observations by expanding the range of T1-values to 9.4 T. In Fig. 3, a comparison of PCr T1-values from selected studies [1, 3–5] demonstrates the field dependence of T1 from 3 to 9.4 T. This data illustrates the added value for ultra-high field for 31P examinations.