Biology subjects

Lazeyras, F.

Publications and source records attributed to Lazeyras, F..

5 recordsLinked to original sources

bioRxiv2025

Regional BOLD variability reflects microstructural maturation and neuronal ensheathment in the preterm infant cortex

BOLD variability reflects meaningful brain activity, yet its structural and biological correlates during early development remain unknown. We aimed to investigate how BOLD variability evolves in very preterm (VPT) infants, its relationship with cortical microstructure and gene expression, and how it differs from full-term (FT) newborns at term-equivalent age (TEA). Using resting-state fMRI and multi-shell diffusion imaging, acquired in 54 VPT (longitudinally at 33-weeks GA and at TEA) and 24 FT newborns, we evaluated regional differences in cortical BOLD variability and microstructural maturation, and compared to patterns of gene expression in the fetal cortex, using the BrainSpan dataset. BOLD variability increased in primary sensory-sensorimotor and proto-DMN regions, accompanied by decreased cortical diffusivity. Gene expression analysis revealed concurrent upregulation of genes mediating gliogenesis and neuronal ensheathment. Compared to FT newborns, VPT at TEA showed decreased BOLD variability and increased cortical diffusivity. BOLD variability reflects cortical microstructure, mediated by upregulation of gliogenesis and neuronal ensheathment. Interruption of these processes by preterm birth identifies putative mechanisms of preterm brain injury.

neuroscience↗

bioRxiv2020

EEG and fMRI connectomes are reliably related: a simultaneous EEG-fMRI study from 1.5T to 7T

Both electroencephalography (EEG) and functional Magnetic Resonance Imaging (fMRI) are non-invasive methods that show complementary aspects of human brain activity. Despite measuring different proxies of brain activity, both the measured blood-oxygenation (fMRI) and neurophysiological recordings (EEG) are indirectly coupled. The electrophysiological and BOLD signal can map the underlying functional connectivity structure at the whole brain scale at different timescales. Previous work demonstrated a moderate but significant correlation between resting-state functional connectivity of both modalities, however there is a wide range of technical setups to measure simultaneous EEG-fMRI and the reliability of those measures between different setups remains unknown. This is true notably with respect to different magnetic field strengths (low and high field) and different spatial sampling of EEG (medium to high-density electrode coverage). Here, we investigated the reproducibility of the bimodal EEG-fMRI functional connectome in the most comprehensive resting-state simultaneous EEG-fMRI dataset compiled to date including a total of 72 subjects from four different imaging centers. Data was acquired from 1.5T, 3T and 7T scanners with simultaneously recorded EEG using 64 or 256 electrodes. We demonstrate that the whole-brain monomodal connectivity reproducibly correlates across different datasets and that a moderate crossmodal correlation between EEG and fMRI connectivity of r{approx}0.3 can be reproducibly extracted in low- and high-field scanners. The crossmodal correlation was strongest in the EEG-{beta} frequency band but exists across all frequency bands. Both homotopic and within intrinsic connectivity network (ICN) connections contributed the most to the crossmodal relationship. This study confirms, using a considerably diverse range of recording setups, that simultaneous EEG-fMRI offers a consistent estimate of multimodal functional connectomes in healthy subjects that are dominantly linked through a functional core of ICNs across spanning across the different timescales measured by EEG and fMRI. This opens new avenues for estimating the dynamics of brain function and provides a better understanding of interactions between EEG and fMRI measures. This observed level of reproducibility also defines a baseline for the study of alterations of this coupling in pathological conditions and their role as potential clinical markers.

neuroscience↗

bioRxiv2020

Whole-Brain High-Resolution Metabolite Mapping with 3D Compressed-Sensing-SENSE-LowRank 1H FID-MRSI

There is a growing interest in the neuroscience community to map the distribution of brain metabolites in vivo. Magnetic resonance spectroscopic imaging (MRSI) is often limited by either a poor spatial resolution and/or a long acquisition time which severely limits its applications for clinical or research purposes. Building on a recently developed technique of acquisition-reconstruction for 2D MRSI, we combined fast Cartesian 1H-FID-MRSI acquisition sequence, compressed-sensing acceleration, and low-rank total-generalized-variation constrained reconstruction to produce 3D high-resolution whole-brain MRSI with a significant acquisition time reduction. We first evaluated the acceleration performance using retrospective undersampling of a fully-sampled dataset. Second, a 20 min accelerated MRSI acquisition was performed on the brain of three healthy volunteers resulting in metabolite maps with 5 mm isotropic resolution. The metabolite maps exhibited the detailed neurochemical composition of all brain regions and revealed parts of the underlying brain anatomy. The latter assessment used previous reported knowledge and a brain atlas-based analysis to show consistency of the concentration contrasts and ratio across all brain regions. These results acquired on a clinical 3 Tesla MRI successful combinae of the 3D 1H-FID-MRSI with a constrained reconstruction to produce detailed mapping of metabolite concentrations at high-resolution over the whole brain, with an acquisition time suitable for clinical or research settings.

neuroscience↗

bioRxiv2020

Achieving High-Resolution Whole-Brain Slab 1H-MRSI with Compressed-Sensing and Low-Rank Reconstruction at 7 Tesla

Low sensitivity MR techniques such as magnetic resonance spectroscopic imaging (MRSI) greatly benefit from the gain in signal-to-noise (SNR) provided by ultra-high field MR. High-resolution and whole-brain slab MRSI remains however very challenging due to lengthy acquisition, low signal, lipid contamination and field inhomogeneity. In this study, we propose an acquisition-reconstruction scheme that combines a 1H-FID-MRSI sequence with compressed sensing acceleration and low-rank modeling with total-generalized-variation constraint to achieve metabolite imaging in two and three dimensions at 7 Tesla. The resulting images and volumes reveal highly detailed distributions that are specific to each metabolite and follow the underlying brain anatomy. The MRSI method was validated in a high-resolution phantom containing fine metabolite structures, and in 3 healthy volunteers. This new application of compressed sensing acceleration paves the way for high-resolution MRSI in clinical setting with acquisition times of 5 min for 2D MRSI at 2.5 mm and of 20 min for 3D MRSI at 3.3 mm isotropic.

neuroscience↗

bioRxiv2019

Impact of an intra-abdominal cooling device during open kidney transplantation in pigs

BackgroundKidney transplantation using deceased donors still suffers from high post-operative dysfunction rate. During implantation into the recipient, the kidney rewarms. This second warm ischemia time, which is not monitored, is harmful especially if prolonged. We recently developed an intra-abdominal cooling device that efficiently prevents kidney rewarming during robotic transplantation, and prevent ischemia-reperfusion injuries. Here, we tested the benefits of this cooling device during open kidney transplantation in pigs.\n\nMaterialsKidneys were procured from large pigs by open bilateral nephrectomy. Following procurement, kidneys were flushed with 4{degrees}C Institut Georges Lopez-1 preservation solution, and placed on ice for 128.5 {+/-} 23.2 min. The cooling device was used to continuously cool down the kidney during the vascular anastomosis time.\n\nMethodsAnimals underwent double sequential autologous open renal transplantation with (n = 7) and without (n = 6) intra-abdominal cooling. Renal cortex temperature and urine output were monitored. The severity of the ischemia reperfusion lesions was analyzed by histology (modified Goujon score).\n\nResultsMean anastomosis time was similar between groups (43.9 {+/-} 13 min). At reperfusion, the renal cortex temperature was lower in the group with cooling (4.3 {+/-} 1.1{degrees}C vs 26.5 {+/-} 5.5{degrees}C p <0.001). The cooled kidneys tended to be protected from injury, including some histopathological ischemia-reperfusion lesions. With the device, kidneys had a better immediate post-operative urine output (p=0.05).\n\nConclusionsOur results indicate that the intra-abdominal cooling device significantly reduces second warm ischemic time during transplantation, is technically safe, and does not prolong anastomotic time.

physiology↗