Characterization of macromolecular baseline of human brain using metabolite cycled semi‐LASER at 9.4T

Giapitzakis, IA; Avdievich, NI; Henning, A

doi:10.1002/mrm.27070

Cited by 28 publications

(80 citation statements)

References 56 publications

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“…Additionally, MM tend to have quite short T 2 relaxation times (Behar et al, 1994), and since GABA-edited MRS experiments are normally performed at medium TE (68–80 ms), it has been suggested that the MM signal arises from a mobile form of lysine rather than a bound MM pool (Choi et al, 2007). Some studies have reported regional and tissue-type differences in the MM baseline (Považan et al, 2018, 2015; Schaller et al, 2014), but this is contradicted by other reports (Giapitzakis et al, 2018; Snoussi et al, 2015). Whatever the source of the contaminating MM signal or its heterogeneity across the brain, our results demonstrate that its removal from the edited GABA signal improves the discriminative power of correlational analyses of GABA measurements and behavioral metrics.…”

Section: Discussionmentioning

confidence: 83%

Macromolecule-suppressed GABA measurements correlate more strongly with behavior than macromolecule-contaminated GABA+ measurements

et al. 2018

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The inhibitory neurotransmitter γ-aminobutyric acid (GABA) is known to be fundamental to the neuronal processes underlying visual orientation and vibrotactile frequency and amplitude discrimination. Previous studies have demonstrated that performance on visual and vibrotactile psychophysics tasks is associated with in vivo measurements of "GABA+" levels - a measure of GABA substantially contaminated by a macromolecular (MM) signal. Here, we establish that these prior findings are indeed driven by the GABA fraction of that signal. Edited magnetic resonance spectroscopy (MRS) was used to measure GABA with and without MM suppression in the sensorimotor (SM1) and occipital cortices in 14 healthy male adults. Volunteers also underwent psychophysical experiments to assess their performance on visual orientation discrimination and vibrotactile amplitude and frequency discrimination. We show that MM-suppressed GABA levels correlate more strongly with individual differences in vibrotactile (in the case of SM1 GABA; amplitude: r = -0.63, p = 0.03; frequency: r = -0.62, p = 0.02) and visual orientation (in the case of occipital GABA; r = -0.59, p = 0.05) discrimination thresholds than GABA levels contaminated by MM (vibrotactile amplitude: r = -0.36, p = 0.30; vibrotactile frequency: r = -0.53, p = 0.09; visual orientation: r = 0.21, p = 0.55). These findings further support the view that measurements of endogenous GABA acquired with edited MRS can usefully probe neurochemical-behavioral relationships in humans. Moreover, the more specific measurement of GABA used in this study provides increased statistical power to observe these regionally specific relationships.

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Section: Discussionmentioning

confidence: 83%

Macromolecule-suppressed GABA measurements correlate more strongly with behavior than macromolecule-contaminated GABA+ measurements

et al. 2018

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“…The 3D MPRAGE images were used for the performance of image segmentation (please see MRS data quantification settings section). A spectroscopy voxel (2 × 2 × 2 cm 3 ) was placed in a mixed gray matter (GM) and white matter (WM) area in the lPL (mainly WM) using the appropriate coil configuration described previously . The OccL data used in this paper were acquired during a previous study .…”

Section: Methodsmentioning

confidence: 99%

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

Giapitzakis

Borbáth

Murali‐Manohar

et al. 2018

Magnetic Resonance in Med

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Purpose In this study, the influence of experimentally measured macromolecules and spline baseline on the quantification results of proton MRS data was investigated. Methods Proton MRS spectra from the left parietal lobe and the occipital lobe were acquired at 9.4T in the human brain using metabolite‐cycled semi‐LASER. Then, the left parietal lobe data, along with the occipital lobe, spectra were quantified and the influence of the inclusion of experimentally measured macromolecular basis sets in the fitting model was evaluated. Furthermore, the effect of the stiffness of the fitted spline baselines on the resulting metabolite concentrations was evaluated. Results In general, concentrations were higher for metabolites in occipital lobe than the left parietal lobe. The inclusion of an experimentally acquired measured macromolecular basis set from another brain region neither affected the quantification results nor the resulting spline baselines significantly. A highly flexible spline baseline led to overestimation or underestimation of metabolite concentrations. Differences of above 15% in the quantification of metabolite levels for both lobes were observed for several metabolites using LCModel default settings for spline baselines and macromolecules in comparison to stiffer spline baselines. Conclusion Fitting with the default LCModel macromolecular basis set and spline baseline model had significant influence in the resulting spline baselines, leading to large deviations both in the concentrations and fitted macromolecular components. The number of knots in the spline may create overflexible baselines, which can potentially lead to quantification errors. Interestingly, the interchange of macromolecular basis set between occipital lobe and left parietal lobe spectra had less influence on the quantification results compared to the default LCModel settings.

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“…The most common strategy for measuring the MM spectrum in vivo is to use an inversion recovery sequence, thereby exploiting the short T 1 relaxation times of macromolecules in contrast to those of most brain metabolites . Another approach to capture the macromolecules is to back‐extrapolate the metabolite signal and separate it from the MRSI data .…”

Section: Introductionmentioning

confidence: 99%

“…15,16 The most common strategy for measuring the MM spectrum in vivo is to use an inversion recovery sequence, thereby exploiting the short T 1 relaxation times of macromolecules in contrast to those of most brain metabolites. 8,[17][18][19] Another approach to capture the macromolecules is to back-extrapolate the metabolite signal and separate it from the MRSI data. 20 Afterward, the measured MM spectrum either can be directly included in the basis set as a single component or parameterized and included as several individual MM components, which adds flexibility when the MM content and composition change, for example, when pathologic changes are present.…”

Section: Introductionmentioning

confidence: 99%

Effects of different macromolecular models on reproducibility of FID‐MRSI at 7T

Hečková

Považan²,

Strasser

et al. 2019

Magnetic Resonance in Med

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Purpose A properly characterized macromolecular (MM) contribution is essential for accurate metabolite quantification in FID‐MRSI. MM information can be included into the fitting model as a single component or parameterized and included over several individual MM resonances, which adds flexibility when pathologic changes are present but is prone to potential overfitting. This study investigates the effects of different MM models on MRSI reproducibility. Methods Clinically feasible, high‐resolution FID‐MRSI data were collected in ~5 min at 7 Tesla from 10 healthy volunteers and quantified via LCModel (version 6.3) with 3 basis sets, each with a different approach for how the MM signal was handled: averaged measured whole spectrum (full MM), 9 parameterized components (param MM) with soft constraints to avoid overparameterization, or without any MM information included in the fitting prior knowledge. The test–retest reproducibility of MRSI scans was assessed voxel‐wise using metabolite coefficients of variation and intraclass correlation coefficients and compared between the basis sets. Correlations of concentration estimates were investigated for the param MM fitting model. Results The full MM model provided the most reproducible quantification of total NAA, total Cho, myo‐inositol, and glutamate + glutamine ratios to total Cr (coefficients of variations ≤ 8%, intraclass correlation coefficients ≥ 0.76). Using the param MM model resulted in slightly lower reproducibility (up to +3% higher coefficients of variations, up to −0.1 decreased intraclass correlation coefficients). The quantification of the parameterized macromolecules did not affect quantification of the overlapping metabolites. Conclusion Clinically feasible FID‐MRSI with an experimentally acquired MM spectrum included in prior knowledge provides highly reproducible quantification for the most common neurometabolites in healthy volunteers. Parameterization of the MM spectrum may be preferred as a compromise between quantification accuracy and reproducibility when the MM content is expected to be pathologically altered.

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Characterization of macromolecular baseline of human brain using metabolite cycled semi‐LASER at 9.4T

Cited by 28 publications

References 56 publications

Macromolecule-suppressed GABA measurements correlate more strongly with behavior than macromolecule-contaminated GABA+ measurements

Macromolecule-suppressed GABA measurements correlate more strongly with behavior than macromolecule-contaminated GABA+ measurements

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

Effects of different macromolecular models on reproducibility of FID‐MRSI at 7T

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Characterization of macromolecular baseline of human brain using metabolite cycled semi‐LASER at 9.4T

Cited by 28 publications

References 56 publications

Macromolecule-suppressed GABA measurements correlate more strongly with behavior than macromolecule-contaminated GABA+ measurements

Macromolecule-suppressed GABA measurements correlate more strongly with behavior than macromolecule-contaminated GABA+ measurements

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

Effects of different macromolecular models on reproducibility of FID‐MRSI at 7T

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Macromolecule-suppressed GABA measurements correlate more strongly with behavior than macromolecule-contaminated GABA+ measurements

Macromolecule-suppressed GABA measurements correlate more strongly with behavior than macromolecule-contaminated GABA+ measurements