Neurophotonics最新文献

Significance: Disorders of consciousness (DOCs) pose significant challenges for therapeutic intervention. Spinal cord stimulation (SCS) has emerged as a promising neuromodulation technique for treating DOC patients. However, the selection of optimal SCS stimulation parameters, particularly intensity, lacks objective standards, and considerable variations in the configuration of stimulation intensity are evident among different research groups in previous studies.

Aim: We aim to systematically evaluate the effects of different stimulation intensities of SCS using functional near-infrared spectroscopy (fNIRS) to further optimize the efficacy of SCS.

Approach: Eleven DOC patients with implanted SCS devices were recruited. Four different stimulation intensities based on individual motor thresholds were used: low (50%), threshold (100%), medium (125%), and high (150%). Hemodynamic responses were recorded using fNIRS, and the mean, peak, and net area under the curve values of hemodynamics, as well as the activated channel count, were analyzed, mainly focusing on two regions of interest: the prefrontal cortex (PFC) and the temporo-parietal junction (TPJ).

Results: An inverted U-shaped dose-response curve was observed. The medium-intensity group triggered the most significant hemodynamic responses. The high-intensity group evoked less pronounced responses and showed negative responses post-stimulation. The threshold-intensity group exhibited positive responses but less pronounced than the medium- and high-intensity groups. Conversely, the low-intensity SCS evoked a decreased response. The medium-intensity SCS also resulted in the highest number of activated channels and maintained the highest total hemoglobin concentration level during the inter-stimulus interval. Differences in brain region responses to SCS intensity were observed, with the PFC tolerating higher intensities and the TPJ having a narrower therapeutic window.

Conclusions: Our findings illustrate that the medium-intensity SCS provides the optimal hemodynamic effect. The observed inverted U-shaped dose-response curve underscores the importance of precise parameter adjustments in SCS for DOC patients to maximize efficacy and to avoid overstimulation or insufficient activation.

Lipofuscin, a cellular pigment that accumulates with age, serves as a significant marker of aging. Recently, studies have linked lipofuscin with neurodegenerative diseases, such as Alzheimer's disease (AD). Using an integrated serial sectioning optical coherence tomography (OCT) and two-photon microscopy (2PM) systems, we developed a method to examine the accumulation and distribution of lipofuscin in postmortem human brain samples. Lipofuscin was imaged with 2PM autofluorescence and quantitatively analyzed in specific structures revealed by OCT images. We involved samples from 15 people aged 60 to 90 years, including those with late-stage AD, chronic traumatized encephalopathy (CTE), and controls (NC). We developed a segmentation method for lipofuscin aggregates based on high-pass filtering and adaptive thresholding, achieving a Dice score of 61% using the integrated system at lower resolution when validated against high-resolution fluorescence lifetime imaging microscopy and phasor analysis. Quantitative metrics such as lipofuscin number density, area fraction, and radius were calculated, revealing distinct spatial distribution patterns across different brain regions and neurological conditions. AD cases exhibited a higher accumulation of lipofuscin in the gray matter sulcus regions compared with the controls, represented by the three metrics of density, area fraction, and size. The difference is particularly significant in number density. Furthermore, we discovered that lipofuscin forms layer structures in the cortical gray matter, which may be related to cell distribution in these regions. Further investigation of these areas revealed significant differences in CTE cases, especially in the infragranulary layer sulcus, compared with controls. In contrast to AD cases, the accumulation difference is significant in the sulcus of both the supergranular and infragranular layers compared with controls. These findings provide valuable information on the pathological role of lipofuscin in neurodegeneration.

Significance: During their early stages of development, neurological and neurodegenerative diseases cause changes to the biological tissue's morphology, physiology and metabolism at the cellular level, and acute, transient changes in the local blood flow. The development of optical methods that can image and quantify such changes simultaneously and investigate the relationship among them (neurovascular coupling) in neural tissues can have a profound effect on furthering our understanding of neurodegeneration.

Aim: Our aim is to develop an optical imaging platform for imaging and characterization of neurovascular coupling in the human retina with high spatial and temporal resolutions.

Approach: A compact, clinically viable optical coherence tomography technology was developed for in vivo, simultaneous structural, functional, and vascular imaging of the human retina and was integrated with a clinical electroretinography system. Image processing algorithms were developed to measure visually evoked physiological and blood flow changes in the living retina and explore neurovascular coupling in the healthy human retina.

Results: Both intensity and optical path length changes were measured with optical coherence tomography from most major retinal layers (nerve fiber layer, plexiform layers, inner and outer segments of the photoreceptors, and the retinal pigmented epithelium) in response to a visual stimulation with a 4-ms single white light flash. The visual stimulus also caused fast transient changes in the retinal blood flow in the local blood vessels. The time courses of these changes were similar, and their magnitude was proportional to the intensity of the visual stimulus.

Conclusions: We have developed an optical imaging modality for non-invasive probing of neurovascular coupling in the living human retina and demonstrated its utility and clinical potential in a pilot study on healthy subjects. This imaging platform could serve as a useful clinical research tool for investigation of potentially blinding retinal diseases, as well as neurodegenerative brain diseases that are expressed in the retina such as Alzheimer's and Parkinson's diseases.

Significance: Neonatal brain development plays a crucial role in long-term neurodevelopmental outcomes, particularly in preterm infants.

Aim: We utilized functional near-infrared spectroscopy (fNIRS) to examine the evolution of brain network connectivity in late preterm and term neonates.

Approach: Neonates with a gestational age (GA) between 33 and 41 weeks were included in the study. fNIRS headcaps were placed on the neonates after reaching a stable sleep state. fNIRS data were recorded in continuous-wave mode. Multivariate pattern analysis (MVPA) was conducted to identify distributed patterns of connectivity changes.

Results: Significant developmental changes in brain network connectivity were observed at around 37 weeks of GA, marked by enhanced functional connectivity, particularly within brain network connectivity centered on the parietal lobe (PL). MVPA demonstrated high classification accuracy in distinguishing neonates born before 37 weeks from those born at or after 37 weeks, based on the strength of PL-centered brain connectivity. The accuracy values were as follows: PL = 74.17%, PL-FL = 81.10%, PL-TL = 74.68%, and PL-OL = 67.18%.

Conclusions: These results underscore the critical role of GA in shaping neonatal brain network functional organization and provide valuable insights for early intervention strategies in preterm infants.

Significance: Oxygen metabolism is important to retinal disease development, but current imaging methods face challenges in resolution, throughput, and depth sectioning to spatially map microvascular oxygen.

Aim: We aim to develop a multimodal system capable of simultaneous phosphorescence lifetime imaging scanning laser ophthalmoscopy (PLIM-SLO) and visible light optical coherence tomography (VIS-OCT) to capture capillary-level oxygen partial pressure ( ${\mathrm{pO}}_2$ ) and structural volumes in rodents.

Approach: C57BL/6 mice were imaged by VIS-OCT with high-definition (10 kHz raster) and Doppler (100 kHz circular) protocols. Phosphorescent probe Oxyphor 2P was retro-orbitally injected to enable intravascular PLIM-SLO imaging ( $200\mu s$ pixel dwell time), and a tunable lens was used to adjust the focal depth. The extracted phosphorescence lifetimes were used for ${\mathrm{pO}}_2$ calculation. Simultaneous imaging utilized a shared imaging path and synchronized data collection.

Results: VIS-OCT images revealed detailed anatomy and Doppler shifts, and PLIM-SLO provided capillary ${\mathrm{pO}}_2$ at multiple depths. A hemoglobin oxygen dissociation curve related retinal arterial ${\mathrm{pO}}_2$ to systemic oxygen saturation as inhaled oxygen was varied. Registered simultaneous images were captured, and ${\mathrm{pO}}_2$ was empirically adjusted for the combined excitation.

Conclusion: Detailed anatomical structures and capillary ${\mathrm{pO}}_2$ levels can be simultaneously imaged, providing a useful tool to study oxygen metabolism in rodent disease models.

Significance: Neurovascular coupling matches changes in neural activity to localized changes in cerebral blood flow. Although much is known about the role of excitatory neurons in neurovascular coupling, that of inhibitory interneurons is unresolved. Although neuronal nitric oxide synthase (nNOS)-expressing interneurons are capable of eliciting vasodilation, the role of nitric oxide in neurovascular coupling is debated.

Aim: We investigated the role of nitric oxide in hemodynamic responses evoked by nNOS-expressing interneurons and whisker stimulation in mouse sensory cortex.

Approach: In lightly anesthetized mice expressing channelrhodopsin-2 in nNOS-interneurons, 2D optical imaging spectroscopy was applied to measure stimulation-evoked cortical hemodynamic responses. To investigate the underlying vasodilatory pathways involved, the effects of pharmacological inhibitors of NOS and 20-HETE were assessed.

Results: Hemodynamic responses evoked by nNOS-expressing interneurons were altered in the presence of the NOS inhibitor LNAME, revealing an initial 20-HETE-dependent vasoconstriction. By contrast, the initial sensory-evoked hemodynamic response was largely unchanged.

Conclusions: Our results challenge the involvement of nNOS-expressing interneurons and nitric oxide in the initiation of functional hyperemia, suggesting that nitric oxide may be involved in the recovery, rather than initiation, of sensory-induced hemodynamic responses.

Neurovascular coupling (NVC) ensures the precise delivery of blood to active brain regions and is vital for maintaining cerebral homeostasis. To investigate the dynamic complexity of NVC in vivo, two-photon microscopy (TPM) provides excellent spatial and temporal resolution, enabling detailed visualization of cell-specific interactions and signaling mechanisms in the intact rodent brain. This review details the application of TPM in vascular imaging. We describe surgical preparations and discuss methodological considerations crucial for differentiating vessel types and accurately capturing neurovascular dynamics. Furthermore, we discuss the integration of TPM with genetically encoded fluorescent indicators that promise further advances in elucidating NVC mechanisms in health and disease. Finally, we highlight the recent advances in cutting-edge imaging technologies, which are poised to drive future discoveries in cerebrovascular physiology and pathology.

The editorial introduces the articles in the Neurophotonics Special Issue on Imaging Brain Metabolism and Neuroenergetics.

Understanding molecular transport in the brain in vivo is essential for elucidating how the brain regulates its metabolism, how neurological pathologies develop, and why many brain-targeted drugs fail. Two-photon microscopy (TPM) is the gold standard for in vivo imaging in highly scattering tissues such as the brain. However, suboptimal use of TPM can compromise study outcomes due to the inherent challenges of in vivo imaging. We highlight the importance of optimizing both spatial and temporal resolution in TPM to ensure accurate data acquisition and interpretation. We compare TPM-based studies of molecular transport with traditional wide-field microscopy approaches, emphasizing how light scattering in brain tissue limits the effectiveness of the latter. We discuss the impact of motion blur-arising from diffusion of tracers or natural movement of cerebral vasculature-on image quality and offer practical strategies to mitigate these effects. In addition, we address the complexities of statistically analyzing noisy images, typically occurring due to low-photon budgets or the need for fast image recording in in vivo TPM. We conclude with a set of practical guidelines for effective data acquisition, aimed at facilitating the implementation of the concepts discussed. When properly optimized, TPM is a powerful tool capable of revealing fundamental mechanisms of brain transport and advancing our understanding of cerebral metabolism.

Significance: Capillaries are the critical site of vascular exchange with the local tissue, with continuous flow to meet the brain's unique and steep energetic demands. However, transient stalls in capillary flow have been observed and at elevated levels in preclinical models of disease. Systematic measurements have not been made to quantify the acute effects of individual capillary stalls on local oxygen.

Aim: We aim to quantify oxygen dynamics around capillary stalls as they occur in vivo.

Approach: We use high-resolution two-photon phosphorescent lifetime microscopy (2PLM) to monitor capillary flux and ${\mathrm{pO}}_2$ in the mouse cortex, allowing us to capture acute oxygen dynamics around capillary stalling.

Results: All stalls cause rapid drops in intra-capillary oxygen that likely extend to local tissue based on estimates using the erythrocyte-associated transient (EAT). This includes a subset of capillaries, which reach critically hypoxic levels (<10 mmHg), which could not be predicted by the capillaries' normal flux and oxygen levels, nor local vessel density or proximity to diving arterioles and venules.

Conclusion: Our findings indicate that a subset of capillary stalls reach extremely low local oxygen, resulting in transient hypoxia in the surrounding tissue. This reveals a new potential pathological mechanism due to stalled capillary flow.