Articles 2025

Résumé: Objective: To document the aspect, topography and morphometry of normal human choroidal arteries in the posterior pole by laser Doppler holography (LDH) and OCT. Design: Cross-sectional study. Subjects: Fifty-four eyes of 27 healthy subjects. Methods: A prototypic LDH system captured the laser Doppler shift of the choroidal circulation within the central 20°. Doppler shifts were filtered to extract high velocity vessels. Images of choroidal arteries identified by LDH were subsequently registered with en face and cross-sectional OCT images. Subsequently, the diameters of macular choroidal arteries and their correlation to central choroidal thickness was measured on OCT B-scans. Main Outcome Measures: Spatial disposition, distribution, and diameters of choroidal arteries. Results: Choroidal arteries were identified by LDH and OCT from their emergence from short posterior ciliary arteries (sPCAs), and could be traced to second and third divisions. In the 8 eyes that underwent LDH, 7 of 8 (88%) showed a horizontal first-order artery within 0.5 disc diameter from the fovea. OCT B-scans showed that first-order arteries were located along the sclera-choroid interface; around arteries, the choroidal tissue formed a pyramid-shaped avascular structure with a posterior base contiguous and isoreflective to the sclera. In a cohort of 49 eyes, the diameter of horizontal submacular arteries (average [± standard deviation] 136.3 μm [±47]; range, 70–209 μm) was weakly correlated to central choroidal thickness (P = 0.09). Conclusions: First-order choroidal arteries emerging from sPCAs are located along the sclerochoroidal interface and are surrounded by a pyramid-shaped avascular space, which contributes to differentiate them from veins. The majority of normal eye show a submacular first-order artery running horizontally toward the temporal periphery. These results will pave the way for a better knowledge of diseases affecting the choroidal circulation. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Résumé: Introduction: Kidney histology preparation requires a multistep process that is usually responsible for delayed results. This study introduces dynamic full-field optical coherence tomography (D-FF-OCT) as a label-free alternative to overcome the limitations of traditional histopathology for on-site kidney pathology assessment. Methods: Two patient cohorts were considered, with a total of 31 patients included in the study; one cohort involved patients requiring biopsy of transplant kidney, and the other involved patients requiring biopsy of native kidney. The clinical and biological data were prospectively collected. Histopathological analysis of kidney biopsies was conducted using both conventional stains and dynamic D-FF-OCT imaging. Results: D-FF-OCT enabled the recognition of most kidney structures. The results showed a significant correlation between this technology and conventional stains for the evaluation of both interstitial fibrosis (IF) (r = 0.61, P < 0.001) and tubular atrophy (TA) (r = 0.60, P < 0.001). Although many lesions could be identified such as interstitial inflammation, acute tubular necrosis, glomerular crescents, and vascular intimal thickening; other recognitions such as glomerular membranous deposits, vascular amyloidosis, and peritubular capillaritis will require confirmation in larger cohorts. Conclusion: This study demonstrates the potential of D-FF-OCT imaging for on-site analysis of kidney biopsies, providing rapid and high-resolution images without extensive sample preparation.

Résumé: Microstructures arrayed over a substrate have shown increasing interest due to their ability to provide advanced 3D cellular models, which open up new possibilities for cell culture, proliferation, and differentiation. Still, the mechanisms by which physical cues impact the cell phenotype are not fully understood, hence the necessity to interrogate cell behavior at the highest resolution. However, cell 3D high-resolution optical imaging on such microstructured substrates remains challenging due to their complexity as well as axial calibration issues. In this work, we address this issue by leveraging the geometrical characteristics of fractal-like structures, which serve as axial calibration tools and modulate cell growth. To this end, we use multiscale 3D SiO2 substrates consisting of spatially arrayed octahedral features of a few micrometers to hundreds of nanometers. Through optimizations of both the structures and optical imaging conditions, we demonstrate the potential of these 3D multiscale structures as an alternative to electron microscopy for material imaging but also as calibration tools for 3D super-resolution microscopy. We used their multiscale and known geometry to perform lateral and axial calibrations in 3D single-molecule localization microscopy (SMLM) and assess imaging resolutions. We then utilized these substrates as a platform for high-resolution bioimaging. As a proof of concept, we cultivate human mesenchymal stem cells on these substrates, revealing very different growth patterns compared to flat glass. Specifically, the spatial distribution of cytoskeleton proteins is vastly modified, as we demonstrate with a 3D SMLM assessment.

Résumé: Understanding the mechanisms behind the remote triggering of landslides by seismic waves at micro-strain amplitude is essential for quantifying seismic hazards. Granular materials provide a relevant model system to investigate landslides within the unjamming transition framework, from solid to liquid states. Furthermore, recent laboratory experiments have revealed that ultrasound-induced granular avalanches can be related to a reduction in the interparticle friction through shear acoustic lubrication of the contacts. However, investigating slip at the scale of grain contacts within an optically opaque granular medium remains a challenging issue. Here, we propose an original coupling model and numerically investigate two-dimensional dense granular flows triggered by basal acoustic waves. We model the triggering dynamics at two separated time scales - one for grain motion (milliseconds) and the other for ultrasound (10μs) - relying on the computation of vibrational modes with a discrete element method through the reduction of the local friction. We show that ultrasound predominantly propagates through the strong-force chains, while the ultrasound-induced decrease of interparticle friction occurs in the weak contact forces perpendicular to the strong-force chains. This interparticle friction reduction initiates local rearrangements at the grain scale that eventually lead to a continuous flow through a percolation process at the macroscopic scale - with a delay depending on the proximity to the failure. Consistent with experiments, we show that ultrasound-induced flow appears more uniform in space than pure gravity-driven flow, indicating the role of an effective temperature by ultrasonic vibration.

Résumé: We present a semi-analytical approach to compute quasi-guided elastic wave modes in horizontally layered structures radiating into unbounded fluid or solid media. This problem is of relevance, e.g., for the simulation of guided ultrasound in embedded plate structures or seismic waves in soil layers over an elastic half-space. We employ a semi-analytical formulation to describe the layers, thus discretizing the thickness direction by means of finite elements. For a free layer, this technique leads to a well-known quadratic eigenvalue problem for the mode shapes and corresponding horizontal wavenumbers. Incorporating the coupling conditions to account for the adjacent half-spaces gives rise to additional terms that are nonlinear in the wavenumber. We show that the resulting nonlinear eigenvalue problem can be cast in the form of a multiparameter eigenvalue problem whose solutions represent the wave numbers in the plate and in the half-spaces. The multiparameter eigenvalue problem is solved numerically using recently developed algorithms. Matlab implementations of the proposed methods are publicly available.