Sensitivity of single-voxel 1H-MRS in investigating the metabolism of the activated human visual cortex at 7 T

Mangia, Silvia; Tkáč, Ivan; Gruetter, Rolf; Moortele, Pierre-François Van de; Giove, Federico; Maraviglia, B.; Uğurbil, Kâmil

doi:10.1016/j.mri.2005.12.023

Cited by 126 publications

(178 citation statements)

References 22 publications

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“…2,3,18 During the stimulation period (STIM), the red-black checkerboard, flickering at a frequency of 7.5 Hz and covering the central visual field of view (22 × 29 degrees), was projected on the mirror mounted to the head radio frequency (RF) coil. During the resting condition (REST), only the black background was presented.…”

Section: Visual Stimulationmentioning

confidence: 99%

“…16 Such an approach allowed robust quantification of metabolite concentrations along with their functional changes not only at a group level as achieved in previous investigations, 1,2,4 but also on single subjects, thus enabling the quantification of the correlation between fMRI signals and metabolite concentrations in our group of subjects. The BOLD effect induces a line narrowing of spectra during activation, 17 on the order of 0.4 to 0.5 Hz at 7 T. 2 Since, LCModel quantification can be slightly biased by such changes in linewidth, 18 an artefactual correlation between BOLD signals and metabolite concentration changes is to be expected. In the present study, we therefore assessed the spectral linewidth changes occurring during the functional paradigm for each studied subject rather than at a group level.…”

Section: Introductionmentioning

confidence: 99%

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Neurochemical and BOLD Responses during Neuronal Activation Measured in the Human Visual Cortex at 7 Tesla

Bednařík

Tkáč

Giove

et al. 2015

J Cereb Blood Flow Metab

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177

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Several laboratories have consistently reported small concentration changes in lactate, glutamate, aspartate, and glucose in the human cortex during prolonged stimuli. However, whether such changes correlate with blood oxygenation level-dependent functional magnetic resonance imaging (BOLD-fMRI) signals have not been determined. The present study aimed at characterizing the relationship between metabolite concentrations and BOLD-fMRI signals during a block-designed paradigm of visual stimulation. Functional magnetic resonance spectroscopy (fMRS) and fMRI data were acquired from 12 volunteers. A short echo-time semi-LASER localization sequence optimized for 7 Tesla was used to achieve full signal-intensity MRS data. The group analysis confirmed that during stimulation lactate and glutamate increased by 0.26 ± 0.06 μmol/g (~30%) and 0.28 ± 0.03 μmol/g (~3%), respectively, while aspartate and glucose decreased by 0.20 ± 0.04 μmol/g (~5%) and 0.19 ± 0.03 μmol/g (~16%), respectively. The single-subject analysis revealed that BOLD-fMRI signals were positively correlated with glutamate and lactate concentration changes. The results show a linear relationship between metabolic and BOLD responses in the presence of strong excitatory sensory inputs, and support the notion that increased functional energy demands are sustained by oxidative metabolism. In addition, BOLD signals were inversely correlated with baseline γ-aminobutyric acid concentration. Finally, we discussed the critical importance of taking into account linewidth effects on metabolite quantification in fMRS paradigms. Journal of Cerebral Blood INTRODUCTIONFunctional magnetic resonance spectroscopy (fMRS) is a powerful tool that allows quantifying the dynamic of brain metabolite concentrations in the working brain in vivo. Different laboratories have recently used fMRS at ultra-high magnetic field (7 Tesla (7 T)) to measure the neurochemical responses occurring during stimulation of the human visual cortex. [1][2][3][4] The results of these studies were highly consistent with concentration changes in the order of 0.2 μmol/g being reported for aspartate (Asp), glutamate (Glu), glucose (Glc), and lactate (Lac) during prolonged visual stimuli. Similar changes of Glu and Lac have also been reported in the motor cortex. 5 The observed functional changes of metabolite concentrations support an overall increase in oxidative energy metabolism during neuronal activation. 6 In particular, the opposite changes in Glc and Lac concentrations are thought to reflect increased metabolic rate of Glc utilization and activation of the aerobic glycolytic pathway in brain cells. [7][8][9] The observed decrease in Asp and increase in Glu have been interpreted as a consequence of an increased rate of the malate-aspartate shuttle, which is associated with the increased flux into the tricarboxylic acid (TCA) cycle.

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Section: Visual Stimulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Neurochemical and BOLD Responses during Neuronal Activation Measured in the Human Visual Cortex at 7 Tesla

Bednařík

Tkáč

Giove

et al. 2015

J Cereb Blood Flow Metab

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177

271

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“…One of the key inhibitory metabolites is γ‐aminobutyric acid (GABA), which is the main inhibitory neurotransmitter of the brain and is believed to have a direct impact on BOLD contrast through regulation of neuronal firing rates 6, 7, 8. In the human brain in vivo , the relationship between GABA and BOLD signals has been investigated in studies that combined fMRI and MRS 7, 9, 10, 11, 12, 13, 14, 15…”

Section: Introductionmentioning

confidence: 99%

Maximizing sensitivity for fast GABA edited spectroscopy in the visual cortex at 7 T

et al. 2018

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The combination of functional MRI (fMRI) and MRS is a promising approach to relate BOLD imaging to neuronal metabolism, especially at high field strength. However, typical scan times for GABA edited spectroscopy are of the order of 6‐30 min, which is long compared with functional changes observed with fMRI.The aim of this study is to reduce scan time and increase GABA sensitivity for edited spectroscopy in the human visual cortex, by enlarging the volume of activated tissue in the primary visual cortex. A dedicated setup at 7 T for combined fMRI and GABA MRS is developed. This setup consists of a half volume multi‐transmit coil with a large screen for visual cortex activation, two high density receive arrays and an optimized single‐voxel MEGA‐sLASER sequence with macromolecular suppression for signal acquisition.The coil setup performance as well as the GABA measurement speed, SNR, and stability were evaluated. A 2.2‐fold gain of the average SNR for GABA detection was obtained, as compared with a conventional 7 T setup. This was achieved by increasing the viewing angle of the participant with respect to the visual stimulus, thereby activating almost the entire primary visual cortex, allowing larger spectroscopy measurement volumes and resulting in an improved GABA SNR. Fewer than 16 signal averages, lasting 1 min 23 s in total, were needed for the GABA fit method to become stable, as demonstrated in three participants. The stability of the measurement setup was sufficient to detect GABA with an accuracy of 5%, as determined with a GABA phantom. In vivo, larger variations in GABA concentration are found: 14‐25%. Overall, the results bring functional GABA detections at a temporal resolution closer to the physiological time scale of BOLD cortex activation.

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“…At 7 T, the high signal-to-noise ratio (SNR) and increased spectral dispersion are expected to result in a higher precision of metabolite quantitation and this could allow for investigations of smaller voxel sizes, which better match a specific brain anatomy. However, spectral overlap with the larger resonances of the myo-inositol still hampers the detection of glycine and previous MRS studies performed at 7 T reported no detection of glycine [9,10].…”

Section: Introductionmentioning

confidence: 99%

In vivo measurement of glycine with short echo-time 1H MRS in human brain at 7 T

Gambarota

Mekle

Xin

et al. 2008

Magn Reson Mater Phy

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Object To determine whether glycine can be measured at 7 T in human brain with 1 H magnetic resonance spectroscopy (MRS). Materials and methodsThe glycine singlet is overlapped by the larger signal of myo-inositol. Density matrix simulations were performed to determine the TE at which the myo-inositol signal was reduced the most, following a single spin-echo excitation. 1 H MRS was performed on an actively shielded 7 T scanner, in five healthy volunteers. Results At the TE of 30 ms, the myo-inositol signal intensity was substantially reduced. Quantification using LCModel yielded a glycine-to-creatine ratio of 0.14 ± 0.01, with a Cramér-Rao lower bound (CRLB) of 7 ± 1%. Furthermore, quantification of metabolites other than glycine was possible as well, with a CRLB mostly below 10%. Conclusion It is possible to detect glycine at 7 T in human brain, at the short TE of 30 ms with a single spin-echo excitation scheme.

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Sensitivity of single-voxel 1H-MRS in investigating the metabolism of the activated human visual cortex at 7 T

Cited by 126 publications

References 22 publications

Neurochemical and BOLD Responses during Neuronal Activation Measured in the Human Visual Cortex at 7 Tesla

Neurochemical and BOLD Responses during Neuronal Activation Measured in the Human Visual Cortex at 7 Tesla

Maximizing sensitivity for fast GABA edited spectroscopy in the visual cortex at 7 T

In vivo measurement of glycine with short echo-time 1H MRS in human brain at 7 T

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