Introduction: Single-voxel spectra are commonly phased with the help of a separate acquisition of the high signal-to-noise ratio (SNR) water signal. Compared to a magnitude spectrum, the corresponding phased spectrum has narrower line widths, and has higher SNR for asymmetric echoes. Furthermore, in the case of coupled spins, sign reversals due to J-coupling are more easily detected in a phased spectrum. Methods: To overcome the long scan times of conventional CSI, we present a method based on time-varying readout gradients that rapidly collects the entire k-space data. Thus, in a short scan time compared to the metabolite acquisition, a separate spectroscopic acquisition of the water signal is possible. To combat the adverse effects of RF inhomogeneity on the phase of the spectra, we precede the spiral readout with a spin-echo excitation that is designed to give a stable phase profile in the presence of up to 20% variation in B1. Results: Phase referenced 3D spectroscopic images of N-acetyl aspartate, creatine, and choline were collected from healthy volunteers. Robust phaseing of the spectra was observed. Conclusions: Spectroscopic water reference acquisition with time-varying readout gradients enables a robust volumetric acquisition of automaticllay phased spectra.
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