High temporal resolution functional magnetic resonance spectroscopy in the mouse upon visual stimulation

Simultaneous detection of metabolite concentration changes, water BOLD signal and pH changes during visual stimulation in the human brain at 9.4T

“…Although the methyl protons of these two metabolites overlap with each other (Cr: 3.027 ppm; PCr: 3.029 ppm 74 ) in our spectra, the high SNR and spectral resolution along with a very narrow transition band of the MC pulse allows separate fitting of Cr and PCr based on their methylene peaks (Cr: 3.913 ppm; PCr: 3.930 ppm 74 ). The decrease in the PCr/Cr ratio, which is more pronounced at the onset of stimulation, is consistent with results obtained in 1 H fMRS rodent studies 20–23 and a PCr signal decrease observed in some 31 P fMRS studies in humans. 24–27 PCr serves as a source of high energy phosphates.…”

“…Increased creatine kinase exchange flux due to visual stimulation has also been shown in 31 P magnetization transfer studies in humans at different field strengths. 27,31,33,79 Since our results of PCr and Cr concentration time courses under visual stimulation confirm previous results, 20–27,31,33,79 we used these concentration ratios to additionally calculate pH. The mean pH value of ∼7 calculated is consistent with intracellular pH values reported in 31 P brain studies at 7 T and 9.4 T. 80–82 Under the assumption of a constant ATP/ADP ratio, we also calculated pH time courses.…”

“…Besides Lac and Glu concentration changes, animal 1 H fMRS studies conducted at UHFs between 9.4 T and 14.7 T report a decrease of the phosphocreatine (PCr) concentration and an increase in the creatine (Cr) concentration during brain activation. 20–23 The observed downregulation of PCr during stimulation is consistent with some phosphorus ( 31 P) fMRS studies in the human brain, 24–27 while others did not observe this downregulation. 28–31 31 P fMRS studies not only report contradictory results on metabolite concentration changes but also for pH estimates.…”

Functional MRS studies of GABA and Glutamate/Glx – a systematic review and meta-analysis

“…Block designs have the advantage of robust metabolite quantification as signal averaging is performed during a sustained stimulus, typically over a period of over 5 minutes. However, habituation and adaptation to repeated stimulation likely plays a key role in block designs (Michels et al, 2012; Betina Ip et al, 2017; Ligneul et al, 2021). Furthermore, signal averaging over a longer time course has been shown to smooth out any task-based dynamics of neural activity (Mangia et al, 2007; Mullins, 2018).…”

The Future is 2D: Spectral-Temporal Fitting of Dynamic Magnetic Resonance Spectroscopy Data Provides Exponential Gains in Precision Over Conventional Approaches

“…Dynamic Magnetic Resonance Spectroscopy refers to an experiment by which a series of one dimensional spectra are acquired sequentially, often while varying a sequence parameter or administering an external time-dependent stimulus or manipulation. This encompasses a wide range of experimental designs, including the observation of the dynamic incorporation of 13 C or 2 H-labeled metabolites following the injection of a labeled compound (1-7); Functional MRS, designed to detect endogenous metabolic changes in glutamate, GABA and lactate in response to an external visual, motor or cognitive manipulation (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20); Multiparametric magnetic resonance spectroscopic experiments, aimed at simultaneously and efficiently quantifying multiple spin parameters (21)(22)(23)(24)(25)(26); Diffusion MRS, whereby the diffusion-weighting gradients are varied to quantify the diffusion coefficient of different metabolites (27)(28)(29)(30)(31)(32); and even simple relaxometry, where, e.g., T 2 might be measured by measuring spectral data at different echo times (MTE) (33)(34)(35)(36)(37)(38)(39)(40)(41).…”