Characterization and correction of center‐frequency effects in X‐nuclear eddy current compensations on a clinical MR system. Issue 5 (4th December 2020) - McLean, Mary A.
Abstract : Purpose: The aim of the study was to investigate whether incorrectly compensated eddy currents are the source of persistent X‐nuclear spectroscopy and imaging artifacts, as well as methods to correct this. Methods: Pulse‐acquire spectra were collected for 1 H and X‐nuclei ( 23 Na or 31 P) using the minimum TR permitted on a 3T clinical MRI system. Data were collected in 3 orientations (axial, sagittal, and coronal) with the spoiler gradient at the end of the TR applied along the slice direction for each. Modifications to system calibration files to tailor eddy current compensation for each X‐nucleus were developed and applied, and data were compared with and without these corrections for: slice‐selective MRS (for 23 Na and 31 P), 2D spiral trajectories (for 13 C), and 3D cones trajectories (for 23 Na). Results: Line‐shape distortions characteristic of eddy currents were demonstrated for X‐nuclei, which were not seen for 1 H. The severity of these correlated with the amplitude of the eddy current frequency compensation term applied by the system along the axis of the applied spoiler gradient. A proposed correction to eddy current compensation, taking account of the gyromagnetic ratio, was shown to dramatically reduce these distortions. The same correction was also shown to improve data quality of non‐Cartesian imaging (2D spiral and 3D cones trajectories). Conclusion: A simple adaptation of the default compensation for eddy currents was shown to eliminate a range of artifacts detected on X‐nuclear spectroscopy and imaging.