Prospective motion and B₀ shim correction for MR spectroscopy in human brain at 7T

Abstract

Purpose To demonstrate feasibility and performance of prospective motion and B0 shim correction for MRS in human brain at 7T. Methods Prospective motion correction using an optical camera and linear B0 shim correction using FASTMAP‐like navigators were implemented into a semi‐LASER sequence. The effect of motion on spectral quality was assessed without and with prospective correction in prefrontal cortex in 11 subjects. Results Without prospective motion and shim correction, motion resulted in considerable degradation of MR spectra (broader linewidth, lower signal‐to‐noise ratio, degraded water suppression). With prospective motion and shim correction, spectral quality remained excellent despite motion. Prospective motion correction alone was not sufficient to prevent degradation of spectral quality. Conclusion Prospective motion and B0 shim correction is feasible at 7T and should help improve the robustness of MRS, particularly in motion‐prone populations.

Motion correction in magnetic resonance spectroscopy

“…Finally, using a similar optical tracking system and marker, Deelchand et al 67 performed prospective motion and shim correction in the human brain using the semi‐LASER sequence at 7 T; more details are described subsequently 67 …”

“…By applying real‐time motion and shim corrections, the navigated MRSI sequences yielded data with good spectral quality in the presence of scanner and subject instabilities compared with the nonnavigated sequences. Finally, Deelchand et al 67 used optical tracking and FASTMAP‐like navigators to perform prospective motion and shim correction in the human brain using the semi‐LASER sequence at 7 T. Again, in the presence of large movements, motion correction alone was not sufficient in preventing degradation of data quality, but data quality remained excellent with simultaneous motion and shim correction 67 …”

“…By applying real-time motion and shim corrections, the navigated MRSI sequences yielded data with good spectral quality in the presence of scanner and subject instabilities compared with the nonnavigated sequences. Finally, Deelchand et al 67 used optical tracking and FASTMAP-like navigators to perform prospective motion and shim correction in the human brain using the semi-LASER sequence at 7 T. Again, in the presence of large movements, motion correction alone was not sufficient in preventing degradation of data quality, but data quality remained excellent with simultaneous motion and shim correction. 67 Prospective frequency-correction and B 0 -correction techniques are important for spectral editing sequences, because they ensure that f cs pulses are applied correctly at the editing target (eg, 4.56 ppm for GSH editing) and minimize spectral interference with co-edited signals (eg, GSH-edited signal at 2.95 ppm and co-edited NAA signal at 2.6 ppm).…”

MR spectroscopy using static higher order shimming with dynamic linear terms (HOS‐DLT) for improved water suppression, interleaved MRS‐fMRI, and navigator‐based motion correction at 7T

“…We did observe an increase in linewidth after motion despite performing motion correction, which was likely due to motion‐induced shim changes. Therefore, a potential next step would be to investigate dynamic shim updating in response to motion‐induced shim changes …”

“…Similarly, global field homogeneity is important when performing motion corrected MRS using interleaved MR‐based navigators. Although motion correction is possible using external tracking devices, MR navigators have the advantage that they are inherently acquired in the scanner coordinate system. Also they do not require additional hardware or the use of markers, while still showing a significant improvement in clinical scoring of motion corrupted scans .…”