• Chu-Yu Lee, In-Young Choi, and Phil Lee.
• Hoglund Brain Imaging Center, University of Kansas Medical Center, Kansas City, Kansas.
• Magn Reson Med. 2018 Dec 1; 80 (6): 2366-2373.

PurposeNew frequency correction methods are required to achieve the accurate measurement of frequency drifts in MRS and MRSI. We present a prospective frequency correction method with outer volume suppression (OVS)-based localization and selective water excitation for effective frequency correction with better SNR improvement compared to other techniques.MethodsAn OVS-localized navigator was developed to prospectively correct frequency drifts during MRS and MRSI measurements. The performance of the navigator was tested on the human brain and a solution phantom for frequency drifts induced by head motion or gradient heating by a preceding DWI experiment at 3T.ResultsThe OVS-localized navigator could accurately track motion-induced frequency drifts with an RMS error of 0.5 Hz. The SNR of MRS signals was not affected by use of the OVS-localized navigator when compared with and without the navigator (P > 0.05). The frequency drifts induced by DWI experiments were 5.1 ± 0.3 Hz/min during MRSI measurements on humans, resulting in increased spectral linewidth, significant bias in metabolite concentrations, and significantly increased Cramér-Rao lower bounds (P < 0.05). After prospective frequency corrections, the quality of MRSI was recovered to the level of those without any DWI-induced frequency drifts, judged by the spectral linewidth, metabolite concentrations, and Cramér-Rao lower bounds.ConclusionThe OVS-localized navigator demonstrated effective prospective frequency corrections for large frequency drifts (5 Hz/min) without introducing any saturation-induced SNR loss. These benefits can be particularly beneficial for the acquisition of MRS signals with long T1 and/or short TR, and spectral editing.© 2018 International Society for Magnetic Resonance in Medicine.

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