Kimberly L Chan¹, Hanzhang Lu², Zixuan Lin², Anke Henning^3,4, and Binu P Thomas^1
1Advanced Imaging Research Center, The University of Texas Southwestern, Dallas, TX, United States, ²Johns Hopkins University, Baltimore, MD, United States, ³The University of Texas Southwestern, Dallas, TX, United States, ⁴Max Planck Institute for Biological Cybernetics, Tübingen, Germany

The relationship between brain’s GABA and glutamate/glutamine (Glx) concentrations measured by 1H MRS, hemodynamic response, neural signaling, and behavior is poorly understood. Here, the relationship between MRS-detectable GABA and Glx signals and MR hemodynamic contrasts during visual stimulation were examined.  It was observed that changes in GABA+ and Glx were positively correlated with the BOLD response and negatively correlated with their levels at rest. Additionally, task GABA+ concentrations were negatively correlated with cerebral metabolic rate of oxygen (CMRO2). Together, these results suggest shifts in the inhibitory/excitatory balance and metabolism to maintain homeostasis in the brain.

Eloïse MOUGEL¹ and Julien Valette^1
1Université Paris-Saclay, Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA), Centre National de la Recherche Scientifique (CNRS), Molecular Imaging Research Center (MIRCen), Laboratoire des Maladies Neurodégénératives, Fontenay aux Roses, France

 Being more specific to cellular microstructure than water diffusion, diffusion-weighted spectroscopic imaging (DW-MRSI) is a powerful tool for measuring disorders in cortical gray matter. Nevertheless, measurement in the cortex is difficult due to its proximity to the skull. We propose a selective DW-MRSI sequence, which avoids lipid contamination and measures the signal of metabolites even in the cortex. We performed an in vivo acquisition with this sequence and were able to measure an apparent diffusion coefficient over an entire brain slab.

William T Clarke¹, Clémence Ligneul¹, Michiel Cottaar¹, and Saad Jbabdi^1
1Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom

Dynamic magnetic resonance spectroscopy acquires multiple spectra under changing experimental conditions. Examples include editing, functional MRS, and diffusion weighted MRS. In this work we introduce a new tool that allows direct fitting of a dynamic signal model to multiple spectra simultaneously. Incorporation of a dynamic model into multi-spectra fitting reduces the number of parameters to be estimated from noisy data, reducing overall uncertainty. 

 

The tool is demonstrated on simulated and multi-subject in vivo datasets, highlighting the high flexibility of the tool, which is open source and available as part of the FSL-MRS toolbox.

Junjie Ma¹, Marco C. Pinho^1,2, Crystal E. Harrison¹, Jun Chen¹, Galen D. Reed³, Albert P. Chen³, A. Dean Sherry^1,4, Craig R. Malloy^1,2,5, Christopher J. Madden⁶, and Jae Mo Park^1,2,7
1Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States, ²Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ³GE Healthcare, Dallas, TX, United States, ⁴Biochemistry and Chemical Biology, UT Dallas, Richardson, TX, United States, ⁵Internal Medicine, UT Southwestern Medical Center, Dallas, TX, United States, ⁶Neurological Surgery, UT Southwestern Medical Center, Dallas, TX, United States, ⁷Electrical and Computer Engineering, UT Dallas, Richardson, TX, United States

This study demonstrates that time-resolved ¹³C MR spectroscopy with the multichannel ¹³C/¹H RF coils can be performed as an alternative to imaging for assessing pyruvate metabolism using hyperpolarized [1-¹³C]pyruvate in the human brain.

Rudy Rizzo^1,2 and Roland Kreis^1,2
1Magnetic Resonance Methodology, Institute of Diagnostic and Interventional Neuroradiology, University of Bern, Bern, Switzerland, ²Translational Imaging Center, sitem-insel, Bern, Switzerland

Multi-Echo Single-Shot (MESS) spectroscopy is tested in-vivo aiming at simultaneous determination of metabolite content and T₂ times through simultaneous multi-parametric model fitting of partially sampled echoes. Cramer-Rao Lower Bounds (CRLBs) are used as measure of performances. The novel scheme was compared with the traditional Multi-Echo Multi-Shot (MEMS) method. Results confirmed former in-silico studies and indicate that MESS outperforms MEMS for simultaneous determinations of T₂s and concentrations, with improvements ranging from 5-20% for T₂s and 10-50% for concentrations.

Eloïse MOUGEL¹, Sophie Malaquin¹, and Julien Valette^1
1Université Paris-Saclay, CEA, CNRS, MIRCen, Laboratoire des Maladies Neurodégénératives, Fontenay aux Roses, France

Little or no correlation exists between diffusion and T₂ relaxation of intracellular brain metabolites, as measured by MRS. However, for lactate, which is both intracellular and extracellular, some correlation might exist, which would be crucial to interpret lactate diffusion. Using a frequency-selective diffusion-weighted (DW) MRS sequence that removes J-modulation on the lactate peak at 1.3 ppm, thus preserving lactate signal even at long TE, we investigated the effect of echo time TE on lactate diffusion-weighted attenuation, for TE between 50.9 and 110.9 ms. It appears that the effect of TE on the apparent diffusivity and kurtosis is negligible.