Motion correction methods for MRS: experts' consensus recommendations

Abstract

Long acquisition times due to intrinsically low signal-to-noise ratio and the need for highly homogeneous B 0 field make MRS particularly susceptible to motion or scanner instability compared with MRI. Motion-induced changes in both localization and shimming (ie B 0 homogeneity) degrade MRS data quality. To mitigate the effects of motion three approaches can be employed: (1) subject immobilization, (2) retrospective correction, and (3) prospective real-time correction using internal and/or external tracking methods. Prospective real-time correction methods can simultaneously update localization and the B 0 field to improve MRS data quality. While localization errors can be corrected with both internal (navigators) and external (optical camera, NMR probes) tracking methods, the B 0 field correction requires internal navigator methods to measure the B 0 field inside the imaged volume and the possibility to update the scanner shim hardware in real time. Internal and external tracking can rapidly update the MRS localization with submillimeter and subdegree precision, while scanner frequency and first-order shims of scanner hardware can be updated by internal methods every sequence repetition. These approaches are most well developed for neuroimaging, for which rigid transformation is primarily applicable. Realtime correction greatly improves the stability of MRS acquisition and quantification, as shown in clinical studies on subjects prone to motion, including children and patients with movement disorders, enabling robust measurement of metabolite signals including those with low concentrations, such as gamma-aminobutyric acid and glutathione. Thus, motion correction is recommended for MRS users and calls for tighter integration and wider availability of such methods by MR scanner manufacturers.

Advanced single voxel 1H magnetic resonance spectroscopy techniques in humans: Experts' consensus recommendations

“…Prospectively gated acquisitions 59 are relatively easy to implement and have the advantage of confining the volume of acquisition more precisely to the prescribed volume, but are constrained to use a relatively long T R . Whenever available, prospective volume tracking methods should be used, [60][61][62] ideally in conjunction with dynamic linear shim corrections, 63 because even when the VOI position is updated in real time, the spectral quality can degrade substantially without dynamic shim updates. 64 4.4 | Recommendations for data analysis: QC…”

Real‐time motion and retrospective coil sensitivity correction for CEST using volumetric navigators (vNavs) at 7T

“…The main advantage of prospective methods is the direct measurement of the desired k‐space data, avoiding estimation errors because of missing k‐space data 20,46 . Additionally, the combination of prospective and retrospective methods can be advantageous to correct residual errors of the prospective system 17,47 Correction of temporal changes in receiver coil sensitivities: a dynamic normalization factor was derived from interleaved M 0 magnitude acquisitions and further applied to the dynamic glucose‐enhanced (DGEρ) contrast metric.…”

“…Several approaches have been proposed to mitigate motion artifacts in MR imaging and spectroscopy. [15][16][17] They can be divided into prospective and retrospective methods. Prospective strategies track the displacement of the object and allow the update of the slice position and orientation in real-time by adjusting magnetic field gradients and RF pulses.…”

“…Several approaches have been proposed to mitigate motion artifacts in MR imaging and spectroscopy 15‐17 . They can be divided into prospective and retrospective methods.…”

Proton magnetic resonance spectroscopy in skeletal muscle: Experts' consensus recommendations

“…More details can be found in excellent review articles and textbooks that describe the general basics of 1 H-MRS, [29][30][31][32] including other papers in this special issue. [33][34][35][36][37][38][39] Only muscle-specific facets of these issues that arise from the highly structured anatomy and the unique physiology and metabolism of skeletal muscle are discussed in the following sections.…”