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Abstract:
Purpose/Introduction: Non-water suppressed metabolite cycled
proton magnetic resonance spectroscopy (MC 1H-MRS) enables shotby-shot frequency and phase alignment due to the simultaneous acquisition of water and metabolite spectra [1] enhancing both frequency resolution and signal to noise ratio (SNR). In a previous study the adiabatic inversion pulse for MC 1H-MRS was optimized to exploit these advantages for application in the human brain at 9.4T
[2]. In this work, we examine the performance of STEAM [3] based MC 1H-MRS compared to water suppressed 1H-MRS using a
numerically optimized short water suppression (WS) sequence in human brain at 9.4T.
Subjects and Methods: All experiments were conducted using a 4 channel transceiver array coil connected to a whole body 9.4 Tesla Magnetom SIEMENS scanner. For 1H MRS localization a STEAM sequence (TE/TM/TR: 10/50/3000 ms) was used. An optimized water suppression scheme was developed resulting in a WS scheme with duration of 190 ms. The WS scheme was tested on a spherical phantom filled with an aqueous solution of acetate and lactate (Fig. 1). Finally, both sequences were applied on 4 healthy volunteers
(Figs. 2, 3) placing a grey matter voxel in the occipital lobe.
Results: She simultaneously acquired water reference of MC data allowed frequency and phase alignment for the different averages (Fig. 2) leading to a linewidth of 25.9 Hz and SNR of 38.2. Additionally, the MC technique provided a WS factor of 99.8 . On the other hand, the WS spectrum resulted in a linewidth of 28.9 Hz (+3 Hz), SNR of 33.3 (-5 dB) and a WS factor of 99.7 . The difference in SNR and linewidth mainly arises from physiological and volunteer motion demonstrating the importance of the simultaneous
acquisition of water reference spectrum both for the ECC and averaging of the acquisitions (Fig. 2). The MC data enabled the reconstruction of high frequency resolution spectra similar to other studies conducted on 9.4T [4].
Discussion/Conclusion: The conclusions of this study are: (1) MC 1H-MRS enables phase and frequency alignment of individual acquisitions and ECC of the spectrum at 9.4T, (2) MC 1H-MRS performs better in terms of SNR and line width and thus effective spectral resolution compared to WS 1H-MRS and (3) MC 1H-MRS results in a spectrum free of gradient modulation sidebands and eddy current artefacts and excellent WS performance.
