Real-time Correction of Motion and Imager Instability Artifacts during 3D γ-Aminobutyric Acid–edited MR Spectroscopic Imaging

Abstract

Purpose To compare the involuntary head motion, frequency and B shim changes, and effects on data quality during real-time-corrected three-dimensional γ-aminobutyric acid-edited magnetic resonance (MR) spectroscopic imaging in subjects with mild cognitive impairment (MCI), patients with Parkinson disease (PD), and young and older healthy volunteers. Materials and Methods In this prospective study, MR spectroscopic imaging datasets were acquired at 3 T after written informed consent was obtained. Translational and rotational head movement, frequency, and B shim were determined with an integrated volumetric navigator. Head motion patterns and imager instability were investigated in 33 young healthy control subjects (mean age ± standard deviation, 31 years ± 5), 34 older healthy control subjects (mean age, 67 years ± 8), 34 subjects with MCI (mean age, 72 years ± 5), and 44 patients with PD (mean age, 64 years ± 8). Spectral quality was assessed by means of region-of-interest analysis. Group differences were evaluated with Bonferroni-corrected Mann-Whitney tests. Results Three patients with PD and four subjects with MCI were excluded because of excessive head motion (ie, > 0.8 mm translation per repetition time of 1.6 seconds throughout >10 minutes). Older control subjects, patients with PD, and subjects with MCI demonstrated 1.5, 2, and 2.5 times stronger head movement, respectively, than did young control subjects (1.79 mm ± 0.77) (P < .001). Of young control subjects, older control subjects, patients with PD, and subjects with MCI, 6%, 35%, 38%, and 51%, respectively, moved more than 3 mm during the MR spectroscopic imaging acquisition of approximately 20 minutes. The predominant movements were head nodding and "sliding out" of the imager. Frequency changes were 1.1- and 1.4-fold higher in patients with PD (P = .007) and subjects with MCI (P < .001), respectively, and B shim changes were 1.3-, 1.5-, and 1.9-fold higher in older control subjects (P = .005), patients with PD (P < .001), and patients with MCI (P < .001), respectively, compared with those of young control subjects (12.59 Hz ± 2.49, 3.61 Hz · cm ± 1.25). Real-time correction provided high spectral quality in all four groups (signal-to-noise ratio >15, Cramér-Rao lower bounds < 20%). Conclusion Real-time motion and B monitoring provides valuable information about motion patterns and B field variations in subjects with different predispositions for head movement. Immediate correction improves data quality, particularly in patients who have difficulty avoiding movement. RSNA, 2017 Online supplemental material is available for this article.

Whole-slice mapping of GABA and GABA+ at 7T via adiabatic MEGA-editing, real-time instability correction, and concentric circle readout

“…In addition to the SNR loss caused by line broadening, subtraction errors of misaligned spectra lead to improperly subtracted Cr signals, and hence, an overestimation and variability of GABA signals. Older, healthy subjects and, in particular, patients with Parkinson's disease or mild cognitive impairment showed up to 2.5-fold more involuntary head movement than young healthy volunteers (Heckova et al, 2018).…”

“…By co-registering and comparing navigator images acquired interleaved with the MRSI scan, updates (i.e., head translation, rotation, B 0 frequency, and first-order shimming) are calculated in real-time on the scanner and applied before the subsequent MRSI repetition for each TR. vNavs have been shown to improve data quality by reducing subtraction artifacts, especially in patients with a predisposition for movement (Bogner et al, 2014;Heckova et al, 2018;Hnilicová et al, 2016).…”

“…Uncorrected subject head motion and B 0 field changes degrade edited MRSI data Heckova et al, 2018;Puts et al, 2012) and are a substantial source of measurement bias in MRI in general (Zaitsev et al, 2015). In addition to the SNR loss caused by line broadening, subtraction errors of misaligned spectra lead to improperly subtracted Cr signals, and hence, an overestimation and variability of GABA signals.…”

Intra‐session and inter‐subject variability of 3D‐FID‐MRSI using single‐echo volumetric EPI navigators at 3T

“…One of the most common sources of artifacts in MRSI is subject motion. Motion artifacts are less obvious to recognize in MRSI compared to MR imaging, but can nevertheless severely degrade localization accuracy and spectral quality (e.g., line broadening, lipid contamination, and spectral peak splitting) . Rapid gradient switching within a heavy duty cycle sequence (e.g., CRTs, spirals, echo‐planar spectroscopic imaging [EPSI]) causes temporal B 0 changes because of heating of the gradient coils and passive shims .…”

Combining multiband slice selection with consistent k‐t‐space EPSI for accelerated spectral imaging

“…This analysis lies beyond the scope of the current work. However, the EPSI sequence topology can be easily expanded by adding navigators to each of the acquisition blocks, which can track and assist in correction motion artifacts …”