Metabolite‐cycled STEAM and semi‐LASER localization for MR spectroscopy of the human brain at 9.4T

Abstract

This work introduces a novel methodology for single-voxel MRS on a 9.4T whole-body scanner and highlights the advantages of semi-LASER compared to STEAM in terms of excitation profile. In comparison with MC-STEAM, MC-semi-LASER yields spectra with higher SNR. Magn Reson Med 79:1841-1850, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Combination of surface and ‘vertical’ loop elements improves receive performance of a human head transceiver array at 9.4 T

“…In vivo metabolite‐cycled semi‐localized adiabatic selective refocusing (LASER) spectra (TR = 6000 ms; TE = 24 ms) were acquired from eight volunteers (aged 28 ± 3 years) from both the occipital lobe (Occ) and the left parietal lobe (lPar). The data were preprocessed using in‐house software . The SNR of the spectra was measured using the amplitude of the water signal retrieved from the metabolite cycling scheme divided by the standard deviation of the noise measured between –4.8 and 0 ppm.…”

Investigation of the influence of macromolecules and spline baseline in the fitting model of human brain spectra at 9.4T

“…5 The OccL data used in this paper were acquired during a previous study. 2 First and second order B 0 shimming was performed using FASTE(ST)MAP, 18 and voxel-based power calibration was executed. 19 Next, localized 1 H-MRS spectra using MC-semi-LASER with a TE of 24 ms 2 were acquired from each volunteer ( Figure 1).…”

“…For this study, 1 H‐MRS spectra from the left parietal lobe (lPL) of the human brain were acquired from eight healthy volunteers at 9.4T using metabolite‐cycled semi‐LASER (MC‐semi‐LASER) for the first time. Then, the lPL data along with OccL spectra, acquired from the same volunteers in another study, were quantified and the influence of the inclusion of experimentally measured MMBs from both regions in the fitting model was evaluated. Furthermore, the effect of the stiffness of the additionally fitted spline baseline on the resulting concentrations of the metabolites was investigated.…”

“…Proton MRS ( 1 H-MRS) studies at 9.4T reported concentrations of 18 metabolites from spectra acquired from the occipital lobe (OccL) of the human brain. 1,2 The performance of MRS studies in OccL at UHF is facilitated from the achievement of high excitation profiles in this brain region, by partial volume arrays, and by its distance (~30-40 mm) from the surface of the skull. In contrast, in deeper brain locations such as the anterior cingulate cortex or medial parietal lobe, a sufficiently high excitation profile is more difficult to achieve due to the decreased transmission efficiency at UHF in more distant locations.…”

“…6,9 At low static magnetic fields, MM in 1 H-MRS spectra can be sufficiently handled by different fitting software such as LCModel, using simulated macromolecule resonances, 10,11 and polynomial functions (e.g., splines) for addressing additional broad peaks not included in the fitting model. These polynomial functions, named hereafter spline baseline, are designed "to account for a wide variety of unpredictable complications, including: (1) artifacts in the data; (2) substances not present in the basis set of model metabolite spectra; (3) substances possibly in the basis set, but with abnormally short T 2 times; (4) inaccuracies in the simulated models for the highly variable lipid and macromolecule signals; (5) incomplete water suppression LCModel Manual (Version 6.3-1M) page 22." 12 Particularly in LCModel, 13 there is a parameter called dkntmn, which is defined as the minimum allowed spacing between spline knots and which controls the stiffness of the spline baseline.…”