PURPOSE:This study proposes a novel, contrast-free Magnetic Resonance Fingerprinting (MRF) method using balanced Steady-State Free Precession (bSSFP) sequences for the quantification of cerebral blood volume (CBV), vessel radius (R), and relaxometry parameters (T   1 $$ {}_1 $$ , T   2 $$ {}_2 $$ , T   2 $$ {}_2 $$ *) in the brain. METHODS:The technique leverages the sensitivity of bSSFP sequences to intra-voxel frequency distributions in both transient and steady-state regimes. A dictionary-matching process is employed, using simulations of realistic mouse microvascular networks to generate the MRF dictionary. The method is validated through in silico and in vivo experiments on six healthy subjects, comparing results with standard MRF methods and literature values. RESULTS:The proposed method shows strong correlation and agreement with standard MRF methods for T   1 $$ {}_1 $$ and T   2 $$ {}_2 $$ values. High-resolution maps provide detailed visualizations of CBV and microvascular structures, highlighting differences in white matter (WM) and gray matter (GM) regions. The measured GM/WM ratio for CBV is 1.91, consistent with literature values. CONCLUSION:This contrast-free bSSFP-based MRF method offers an new approach for quantifying CBV, vessel radius, and relaxometry parameters. Further validation against DSC imaging and clinical studies in pathological conditions is warranted to confirm its clinical utility.

Injectable hydrogels have emerged as a promising strategy for treating stroke and neurodegenerative diseases, but their effectiveness depends on precise injection, defect filling, and long-term retention at the target site. While MRI can help visualize hydrogels, distinguishing them from fluid-filled spaces, like a post-stroke cavity at a chronic stage, is challenging owing to their high water content and similar MR properties. In this study, a T1 MRI detectable hyaluronic acid (HA) hydrogel that is injectable and self-healing was developed for in vivo tracking after intracerebral injection in stroke. This HA hydrogel was functionalized with a thermodynamically stable and kinetically inert gadolinium(III) complex for monitoring its long-term fate in the brain with T1-contrast enhanced MRI. The dynamic covalent cross-links based on boronate ester bonds in the hydrogel network ensured precise injection and instantaneous self-healing. The HA network did not induce adverse tissue response and was biocompatible with therapeutic cells (human adipose stromal/stem cells). Furthermore, this labeling strategy enabled accurate tracking of hydrogel distribution and degradation in stroke condition, allowing a better assessment of efficacy and safety. This MRI-visible hydrogel has significant potential as a scaffold for stem cells, growth factors, and/or drugs, paving the way for more effective treatments for brain disorders.

Accurate MR signal simulation, including microvascular structures and water diffusion, is crucial for MRI techniques like fMRI BOLD modeling and MR vascular Fingerprinting (MRF), which use susceptibility effects on MR signals for tissue characterization. However, integrating microvascular features and diffusion remains computationally challenging, limiting the accuracy of the estimates. Using advanced modeling and deep neural networks, we propose a novel simulation tool that efficiently accounts for susceptibility and diffusion effects. We used dimension reduction of magnetic field inhomogeneity matrices combined with deep learning method to accelerate the simulations while maintaining their accuracy. We validated our results through an in silico study against a reference method and in vivo MRF experiments. This approach accelerates MR signal generation by a factor of almost 13,000 compared to previously used simulation methods while preserving accuracy. The MR-WAVES method allows fast generation of MR signals accounting for microvascular structures and water-diffusion contribution.

Cerebral amyloid angiopathy (CAA) is a cerebral small vessel disease in which amyloid-β accumulates in vessel walls. CAA is a leading cause of symptomatic lobar intracerebral haemorrhage and an important contributor to age-related cognitive decline. Recent work has suggested that vascular dysfunction may precede symptomatic stages of CAA, and that spontaneous slow oscillations in arteriolar diameter (termed vasomotion), important for amyloid-β clearance, may be impaired in CAA. To systematically study the progression of vascular dysfunction in CAA, we used the APP23 mouse model of amyloidosis, which is known to develop spontaneous cerebral microbleeds mimicking human CAA. Using in vivo 2-photon microscopy, we longitudinally imaged unanesthetized APP23 transgenic mice and wildtype (WT) littermates from 7 to 14 months of age, tracking amyloid-β accumulation and vasomotion in individual pial arterioles over time. MRI was used in separate groups of 12-, 18- and 24-month-old APP23 transgenic mice and WT littermates to detect microbleeds and to assess cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) with pseudo-continuous arterial spin labelling. We observed a significant decline in vasomotion with age in APP23 mice, while vasomotion remained unchanged in WT mice with age. This decline corresponded in timing to initial vascular amyloid-β deposition (∼8–10 months of age), although it was more strongly correlated with age than with vascular amyloid-β burden in individual arterioles. Declines in vasomotion preceded the development of MRI-visible microbleeds and the loss of smooth muscle actin in arterioles, both of which were observed in the majority of APP23 mice by 18 months of age. Additionally, CBF and evoked CVR were intact in APP23 mice at 12 months of age, but significantly lower in APP23 mice by 24 months of age. Our findings suggest that a decline in spontaneous vasomotion is an early, potentially pre-symptomatic, manifestation of CAA and vascular dysfunction, and a possible future treatment target.

Mesial temporal lobe epilepsy (MTLE) is a common drug-resistant epilepsy, often requiring surgery to remove the epileptogenic zone (EZ). The mean efficiency of the surgery is 50-70 %, so the accurate spatial localization of the EZ remains a challenge. In a previous study from Hamelin et al. (2021), gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter, was shown to be highly increased in the EZ of a MTLE mouse model, with a concomitant decrease of Glx (Glutamate + glutamine). The authors proposed the GABA/Glx ratio as a potential specific biomarker of the EZ. As it is the only way to measure GABA and Glx non-invasively in vivo, we propose to use Magnetic Resonance Spectroscopy (MRS) methods to improve the non-invasive localization of the EZ. Our study introduces an original GABA-edited Magnetic Resonance Spectroscopic Imaging (MRSI) method, i.e. the MEGA-LASER CSI, and the dedicated data processing pipeline, to map GABA and Glx in pre-clinical settings. The MEGA-LASER CSI sequence was validated using multi-compartment phantoms with varying GABA concentrations, demonstrating a high accuracy to spatially discriminate the different compartments. In vivo experiments revealed a significant increase of the GABA+/Glx ratio in the EZ of epileptic animals (n=30) compared to SHAM ones (n=15), strongly correlated with ex vivo data. Preliminary immunohistochemistry experiments revealed astrocytic localization of GAD65 in the EZ, suggesting a shift in GABA synthesis from nerve endings to astrocytes. Phantom and in vivo experiments prove that our original workflow for GABA and Glx mapping is suitable for use in neuroscience and pre-clinical applications.

Exercise is a promising strategy for preventing or delaying Alzheimer's disease (AD), yet its mechanisms remain unclear. We investigated how exercise influences brain structure, function, and behavior in a familial AD model. Mice underwent voluntary, voluntary plus enforced exercise, or remained sedentary. Neuroimaging included in vivo manganese-enhanced MRI (MEMRI). perfusion, and ex vivo diffusion MRI to assess morphometry, activity, cerebral blood flow (CBF), microstructural integrity and connectivity.Both exercise regimens induced structural and functional brain adaptations while reducing anhedonia. Voluntary exercise increased cortical and limbic volumes, particularly in the hippocampus, cingulate, and entorhinal cortex, supporting cognitive and emotional regulation. Adding enforced exercise influenced subcortical and sensory regions, including visual, motor and associative areas, supporting sensory-motor integration. MEMRI revealed increased activity in sensorimotor, limbic, and associative cortices, with voluntary exercise enhancing limbic and associative regions, and enforced exercise strengthening sensorimotor and subcortical circuits.White matter integrity improved in memory-associate pathways such as the corpus callosum, cingulum, and hippocampal commissure. Synaptic remodeling was observed in the cingulate cortex, anterior thalamic nuclei, and amygdala. Voluntary exercise enhanced CBF in the motor cortex and hippocampus, while enforced exercise limited these increases.Connectivity analyses revealed exercise-responsive networks spanning the cingulate cortex, entorhinal cortex, anterior thalamic nuclei, and basolateral amygdala, and associated tracts. Graph analyses linked running distance with increased thalamic, brainstem, and cerebellar connectivity, associating exercise intensity with plasticity.These findings highlight the ability of chronic exercise to modulate neuroimaging biomarkers through distinct but complementary pathways, reinforcing its potential as a neuroprotective intervention for AD.

While locating in different microenvironments, glioblastoma stem-like cells (GSCs) receive maintenance signals and information to exploit neurovascular tracts. Although the cell adhesion mechanisms to blood vessels have been explored, the mediators guiding GSC interaction with the endothelial cells and their matrix remain incompletely resolved. Here, we identify junctional adhesion molecule C (JAMC) as a key regulator of heterophilic and homophilic interactions of GSC to endothelial surfaces. Using decellularized matrices, co-cultures, and organotypic brain slices, we demonstrate that JAMC restrains GSC spreading. JAMC-/- GSCs exhibit extended spreading on endothelial-borne supports, with exacerbated invasive, migratory, and mesenchymal-like behaviors, further eroding mice survival. Spatial transcriptomics of human samples confirmed the association between invasion and JAMC expression pattern. Quantitative proteomics unveiled that JAMC deletion elicits integrin upregulation, concurrent with a downregulation of the integrin negative regulator, SHARPIN. The landscape of adhesion molecules anchoring GSCs to vascular surfaces may coordinate cell migration in glioblastoma territories.

PURPOSE:Accurate MR signal simulation, including microvascular structures and water diffusion, is crucial for MRI techniques like fMRI BOLD modeling and MR vascular Fingerprinting (MRF), which use susceptibility effects on MR signals for tissue characterization. However, integrating microvascular features and diffusion remains computationally challenging, limiting the accuracy of the estimates. Using advanced modeling and deep neural networks, we propose a novel simulation tool that efficiently accounts for susceptibility and diffusion effects. METHODS:We used dimension reduction of magnetic field inhomogeneity matrices combined with deep learning methodology to accelerate the simulations while maintaining their accuracy. We validated our results through an in silico study against a reference method and in vivo MRF experiments. RESULTS:This approach accelerates MR signal generation by a factor of almost 13 000 compared to previously used simulation methods while preserving accuracy. CONCLUSION:The MR-WAVES method allows fast generation of MR signals accounting for microvascular structures and water-diffusion contribution.

Focused ultrasound (FUS), in combination with microbubbles, enables the transient and localized opening of the blood-brain barrier (BBB) for targeted drug delivery. While this technique has shown promise in preclinical models, the safety and neurovascular consequences of repeated BBB permeabilization remain incompletely understood. In this study, we performed a longitudinal assessment of vascular, microstructural, and glial responses following repeated FUS-mediated BBB opening in healthy rats using magnetic resonance (MR)-guided targeting and MR vascular fingerprinting. FUS sessions were conducted on a weekly or twice-weekly basis over a period of four weeks, employing two distinct acoustic pressures, 390 kPa and 440 kPa, respectively. The BBB opening was reproducible across sessions, with stable contrast enhancement observed with DCE-MRI and a homogeneous cumulative open BBB volume. No significant hemorrhages or edema were detected; however, transient cerebral blood flow reductions of approximately 15-20 % were observed following each session. After eight FUS sessions at 440 kPa, subtle vascular remodeling was observed, including increased vessel radius and reduced tissue oxygen saturation. This finding was confirmed by both MRI and histological analysis. Astrocytic activation, as determined by GFAP immunostaining, was minimal after a single or weekly FUS exposure but became significant with biweekly treatments, indicating a cumulative neuroimmune response. These results support the feasibility of weekly FUS-induced BBB opening at moderate acoustic pressures. However, they also underscore the importance of protocol optimization to prevent glial and vascular stress in long-term therapeutic applications.

OBJECTIVE:The blood-brain barrier (BBB) is a selectively permeable membrane that restricts drug delivery to the central nervous system. Focused ultrasound (FUS) combined with microbubbles (MBs) is a promising technique to transiently open the BBB, enabling therapeutic delivery. However, real-time monitoring of BBB permeability changes remains challenging. This study investigated the use of indocyanine green (ICG) as a bi-modal contrast agent for photoacoustic and fluorescence imaging to assess BBB opening and closure dynamics. METHODS:BALB/c mice underwent FUS-mediated BBB opening with different doses of MBs and ICG administration. Photoacoustic and fluorescence imaging were performed at various time points post-FUS to evaluate ICG extravasation dynamics. Magnetic resonance imaging (MRI) with gadolinium contrast was used as the gold standard for BBB permeability assessment. The effect of MB dose and injection timing on BBB closure kinetics was analyzed. RESULTS:Photoacoustic imaging provided reliable BBB monitoring within the first hour post-FUS, whereas fluorescence imaging was more effective at detecting ICG extravasation at 24 h. A strong correlation was observed between fluorescence intensity and MRI-based contrast enhancement, confirming BBB opening dynamics. BBB closure followed an exponential decay model, with a half-closure time of approximately 81 min. The degree of BBB opening was proportional to the MB dose administered. CONCLUSION:ICG-based photoacoustic and fluorescence imaging provide a non-invasive and cost-effective alternative to MRI for monitoring FUS-induced BBB opening. These techniques offer complementary temporal windows for assessment, improving the precision of BBB permeability evaluation in preclinical and potentially clinical applications.

Despite the regular discovery of new molecules, one-third of epileptic patients are resistant to antiepileptic drugs. Only a few can benefit from resective surgery, the current gold standard. Although effective in 50–70% of cases, this therapy remains risky, costly, and can be associated with long-term cognitive or neurological side effects. In addition, patients are increasingly reluctant to have a craniotomy, emphasizing the need for new less invasive therapies for focal drug-resistant epilepsies. Here, we review different minimally invasive approaches already in use in the clinic or under preclinical development to treat drug-resistant epilepsies. Localized thermolesion of the epileptogenic zone has been developed in the clinic using high-frequency thermo-coagulations or magnetic resonance imaging-guided laser or ultrasounds. Although less invasive, they have not yet significantly improved the outcomes when compared with resective surgery. Radiosurgery techniques have been used in the clinic for the last 20 years and have proven efficiency. However, their efficacy is not better than resective surgery, and various side effects have been reported as well as the potential risk of sudden unexpected death associated with epilepsy. Recently, a new strategy of radiosurgery has emerged using synchrotron-generated X-ray microbeams: microbeam radiation therapy (MRT). The low divergence and high-flux of the synchrotron beams and the unique tolerance to MRT by healthy brain tissues, allows a precise targeting of specific brain regions with minimal invasiveness and limited behavioral or functional consequences in animals. Antiepileptic effects over several months have been recorded in animal models, and histological and synaptic tracing analysis suggest a reduction of neuronal connectivity as a mechanism of action. The possibility of transferring this approach to epileptic patients is discussed in this review.

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Current techniques of neuroimaging, including electrical devices, are either of low spatiotemporal resolution or invasive, impeding multiscale monitoring of brain activity at both single cell and network levels. Overcoming this issue is of great importance to assess brain's computational ability and for neurorehabilitation projects that require real-time monitoring of neurons and concomitant networks activities. Currently, that information could be extracted from functional MRI when combined with mathematical models. Novel methods enabling quantitative and long-lasting recording at both single cell and network levels will allow to correlate the MRI data with intracortical activity at single cell level, and to refine those models. Here, we report the fabrication and validation of ultra-thin, optically transparent and flexible intracortical microelectrode arrays for combining extracellular multi-unit and fMRI recordings. The sensing devices are compatible with large-scale manufacturing, and demonstrate both fMRI transparency at 4.7 T, and high electrical performance, and thus appears as a promising candidate for simultaneous multiscale neurodynamic measurements.

PURPOSE:Synchrotron microbeam radiation therapy (MRT), based on an inhomogeneous geometric and microscopic irradiation pattern of the tissues with high-dose and high-dose-rate x-rays, enhances the permeability of brain tumor vessels. This study attempted to determine the time and size range of the permeability window induced by MRT in the blood-brain (tumor) barrier. METHODS AND MATERIALS:Rats-bearing 9L gliomas were exposed to MRT, either unidirectional (tumor dose, 406 Gy) or bidirectional (crossfired) (2 × 203 Gy). We measured vessel permeability to molecules of 3 sizes (Gd-DOTA, Dotarem, 0.56 kDa; gadolinium-labeled albumin, ∼74 kDa; and gadolinium-labeled IgG, 160 kDa) by daily in vivo magnetic resonance imaging, from 1 day before to 10 days after irradiation. RESULTS:An equivalent tumor dose of bidirectional MRT delivered from 2 orthogonal directions increased tumor vessel permeability for the smallest molecule tested more effectively than unidirectional MRT. Bidirectional MRT also affected the permeability of normal contralateral vessels to a different extent than unidirectional MRT. Conversely, bidirectional MRT did not modify the permeability of normal or tumor vessels for both larger molecules (74 and 160 kDa). CONCLUSIONS:High-dose bidirectional (cross-fired) MRT induced a significant increase in tumor vessel permeability for small molecules between the first and the seventh day after irradiation, whereas permeability of vessels in normal brain tissue remained stable. Such a permeability window could facilitate an efficient and safe delivery of intravenous small molecules (≤0.56 kDa) to tumoral tissues. A permeability window was not achieved by molecules larger than gado-grafted albumin (74 kDa). Vascular permeability for molecules between these 2 sizes has not been determined.

Background:Cerebral amyloid angiopathy (CAA) is a cerebral small vessel disease in which amyloid-β accumulates in vessel walls. CAA is a leading cause of symptomatic lobar intracerebral hemorrhage and an important contributor to age-related cognitive decline. Recent work has suggested that vascular dysfunction may precede symptomatic stages of CAA, and that spontaneous slow oscillations in arteriolar diameter (termed vasomotion), important for amyloid-β clearance, may be impaired in CAA. Methods:To systematically study the progression of vascular dysfunction in CAA, we used the APP23 mouse model of amyloidosis, which is known to develop spontaneous cerebral microbleeds mimicking human CAA. Using in vivo 2-photon microscopy, we longitudinally imaged unanesthetized APP23 transgenic mice and wildtype littermates from 7 to 14 months of age, tracking amyloid-β accumulation and vasomotion in individual pial arterioles over time. MRI was used in separate groups of 12-, 18-, and 24-month-old APP23 transgenic mice and wildtype littermates to detect microbleeds and to assess cerebral blood flow and cerebrovascular reactivity with pseudo-continuous arterial spin labeling. Results:We observed a significant decline in vasomotion with age in APP23 mice, while vasomotion remained unchanged in wildtype mice with age. This decline corresponded in timing to initial vascular amyloid-β deposition (∼8-10 months of age), although was more strongly correlated with age than with vascular amyloid-β burden in individual arterioles. Declines in vasomotion preceded the development of MRI-visible microbleeds and the loss of smooth muscle actin in arterioles, both of which were observed in APP23 mice by 18 months of age. Additionally, evoked cerebrovascular reactivity was intact in APP23 mice at 12 months of age, but significantly lower in APP23 mice by 24 months of age. Conclusions:Our findings suggest that a decline in spontaneous vasomotion is an early, potentially pre-symptomatic, manifestation of CAA and vascular dysfunction, and a possible future treatment target.

Impact: The permeabilization of the BBB to deliver therapeutics with MR-guided FUS redefines therapeutic strategies as it improves patient outcomes. To ensure the best translation towards clinical treatment, the evaluation of hemodynamic modifications in the CNS is necessary to refine treatment parameters. Methods: MR-guided FUS was applied at 1.5 MHz with a 50 ms burst every 1 s to open the BBB. CBF, BVf and ADC parameters were monitored with MRI. Cavitation was monitored with a PCD during the FUS sequence and classified with the IUD index into three cavitation levels. We distinctly applied the FUS in the cortex or the striatum. After the BBB permeabilization, neuroinflammation markers were quantified longitudinally. Results: The BBB was successfully opened in all animals in this study and only one animal was classified as "hard" and excluded from the rest of the study. 30 min after FUS-induced BBB opening in the cortex, we measured a 54% drop in CBF and a 13% drop in BVf compared to the contralateral side. After permeabilization of the striatum, a 38% drop in CBF and a 15% drop in BVf were measured. CBF values rapidly returned to baseline, and 90 min after BBB opening, no significant differences were observed. We quantified the subsequent neuroinflammation, noting a significant increase in astrocytic recruitment at 2 days and microglial activation at 1 day after FUS. After 7 days, no more inflammation was visible in the brain. Conclusion: FUS-induced BBB opening transiently modifies hemodynamic parameters such as CBF and BVf, suggesting limited nutrients and oxygen supply to the CNS in the hour following the procedure.

Adequate perfusion is critical for maintaining normal brain function and aberrations thereof are hallmarks of many diseases. Pseudo-Continuous Arterial Spin Labeling (pCASL) MRI enables noninvasive quantitative perfusion mapping without contrast agent injection and with a higher signal-to-noise ratio (SNR) than alternative methods. Despite its great potential, pCASL remains challenging, unstable, and relatively low-resolution in rodents - especially in mice - thereby limiting the investigation of perfusion properties in many transgenic or other relevant rodent models of disease. Here, we address this gap by developing a novel experimental setup for high-resolution pCASL imaging in mice and combining it with the enhanced SNR of cryogenic probes. We show that our new experimental setup allows for optimal positioning of the carotids within the cryogenic coil, rendering labeling reproducible. With the proposed methodology, we managed to increase the spatial resolution of pCASL perfusion images by a factor of 15 in mice; a factor of 6 in rats is gained compared to the state of the art just by virtue of the cryogenic coil. We also show that the improved pCASL perfusion imaging allows much better delineation of specific brain areas, both in healthy animals as well as in rat and mouse models of stroke. Our results bode well for future high-definition pCASL perfusion imaging in rodents.

In patients suffering absence epilepsy, recurring seizures can significantly decrease their quality of life and lead to yet untreatable comorbidities. Absence seizures are characterized by spike-and-wave discharges on the electroencephalogram associated with a transient alteration of consciousness. However, it is still unknown how the brain responds to external stimuli during and outside of seizures. This study aimed to investigate responsiveness to visual and somatosensory stimulation in Genetic Absence Epilepsy Rats from Strasbourg (GAERS), a well-established rat model for absence epilepsy. Animals were imaged under non-curarized awake state using a quiet, zero echo time, functional magnetic resonance imaging (fMRI) sequence. Sensory stimulations were applied during interictal and ictal periods. Whole-brain hemodynamic responses were compared between these two states. Additionally, a mean-field simulation model was used to explain the changes of neural responsiveness to visual stimulation between states. During a seizure, whole-brain responses to both sensory stimulations were suppressed and spatially hindered. In the cortex, hemodynamic responses were negatively polarized during seizures, despite the application of a stimulus. The mean-field simulation revealed restricted propagation of activity due to stimulation and agreed well with fMRI findings. Results suggest that sensory processing is hindered or even suppressed by the occurrence of an absence seizure, potentially contributing to decreased responsiveness during this absence epileptic process.