Prospective frequency correction using outer volume suppression‐localized navigator for MR spectroscopy and spectroscopic imaging.

Purpose: New 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. Methods: An 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. Results: The 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. Conclusion: The 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. [ABSTRACT FROM AUTHOR]