Exploring the limits to quantitative elastography: supersonic shear imaging in stretched soft strips
Croquette, S., A. Delory, D. A. Kiefer, C. Prada, and F. Lemoult
Physics in Medicine and Biology 70, no. 14 (2025)
Résumé: Objective. Shear wave elastography has enriched ultrasound medical imaging with quantitative tissue stiffness measurements. We aim to explore the limitations that persist related to viscoelasticity, guiding geometry or static deformation. Approach. A nearly-incompressible soft elastomer strip is chosen to mimic the mechanical behaviour of an elongated tissue. A supersonic shear wave scanner measures the propagation of shear waves within the strip. It provides a wide range of shear wave velocities, from 2 to 6 m s<sup>−1</sup>, depending on the frequency, the static strain as well as the orientation of the strip. Main results. To explain these different measurements, the guided wave effect is highlighted and analysed from the dispersion diagrams provided by the spatio-temporal Fourier transform of the raw data. The guided waves are then described using a material model that accounts for both the rheology and the hyperelastic behaviour, and allows to extract the mechanical parameters of the sample. Significance. To overcome some limitations of current elastography, we propose a theoretical framework which allows the simultaneous characterization of the viscoelastic and hyperelastic properties of soft tissues, paving the way for robust quantitative elastography of elongated tissues.
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A new method using pointing area diagrams to characterize and compare ventilation masks used in continuous positive airway pressure treatment for apneic patients
Rouchié, B., M. Fieux, S. Reisberg, Y. Retory, A. Schmidt, B. Piro, G. Mattana, M. Filoche, B. Louis, C. Virbel-Fleischman, and E. Béquignon
European Archives of Oto-Rhino-Laryngology (2025)
Résumé: Purpose
Mask choice is a key parameter in the adaptation of continuous positive airways pressure (CPAP) treatment. Two indicators used to evaluate poor mask tolerance are cutaneous overpressure and unintentional leaks. The main aim of this study was to characterize each mask, thanks to a feedback harvesting method using pointing area diagrams.
Methods
Diagrams showing a face scheme were submitted to 70 health professionals who install masks. They pointed out the areas of cutaneous overpressure and of unintentional leaks for 6 different masks (2 of each type: facial, nasal, pillow). Areas on the face with the highest concentration of points were determined to compare masks, regarding pressure and leak points.
Results
Out of the 396 analyzed diagrams, the nasal bridge was the area with highest pressure points concentration: 33% and 30%, for facial and nasal masks, respectively. Internal canthus was the area with highest leak points concentration: respectively 27% and 41%. On the nasal bridge, there was no significant difference between facial and nasal masks regarding pressure points (74%, 76%, 72%, and 63%). On internal canthus, 31% indicated a leak point for the F20, 40% for the Quattro Air without significant difference whereas the report was increased for the Soft nasal in comparison to the other nasal mask the Mirage FX (61% vs 33% respectively, p < 0.05).
Conclusion
This method could help decision-making of physicians, health professionals and could be useful for manufacturers in the improvement of their products.
Trial registration number
#20240510.
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Label-free metabolic imaging and energy costs in Chlamydomonas
Boccara, M., K. Wostrikoff, B. Bailleuil, and C. Boccara
The European Physical Journal E 48, no. 6-7 (2025)
Résumé: We developed a label-free optical microscopy method to study movements of different frequencies and amplitudes within a cell. We use optical transmission tomography (OTT) that operates in transmission, and we record the changes of signal values of all the pixels of movies taken for a few seconds (dynamic signal). This signal is a metabolic signal in algae as it decreased in the presence of photosystem II inhibitors or when samples were illuminated at wavelengths where the photoreceptors are poorly operative. We used as model organism Chlamydomonas for which mutants are available. We used a mutant deleted of the chloroplastic gene encoding the large subunit of the Rubisco, ΔrbcL. This mutant is unable to fix atmospheric CO<inf>2</inf> and is devoid of pyrenoid. We compared the dynamic signal between wild-type strain and ΔrbcL mutant of Chlamydomonas grown in dark condition and found it to be 5 to 10 times higher. This mutant overproduced starch, and we tempted to associate the metabolic signal to the cost in ATP<inf>eq</inf> consumption for building starch. The method is easy to implement and could be very valuable for studies of phytoplankton in situ or virus-infected cells.
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Hybrid quantum network for sensing in the acoustic frequency range
Novikov, V., J. Jia, T. B. Brasil, A. Grimaldi, M. Bocoum, M. Balabas, J. H. Müller, E. Zeuthen, and E. S. Polzik
Nature 643, no. 8073, 955-960 (2025)
Résumé: Ultimate limits for the sensing of fields and forces are set by the quantum noise of a sensor<sup>1, 2–3</sup>. Entanglement allows for suppression of such noise and for achieving sensitivity beyond standard quantum limits<sup>4, 5, 6–7</sup>. Applicability of quantum optical sensing is often restricted by fixed wavelengths of available photonic quantum sources. Another ubiquitous limitation is associated with challenges of achieving quantum-noise-limited sensitivity in the acoustic noise frequency range relevant for several applications. Here we demonstrate a tool for broadband quantum sensing by performing quantum state processing that can be applied to a wide range of the optical spectrum and by suppressing quantum noise over an octave in the acoustic frequency range. An atomic spin ensemble is strongly coupled to one of the frequency-tunable beams of an Einstein–Podolsky–Rosen (EPR) source of light. The other EPR beam of light, entangled with the first one, is tuned to a disparate wavelength. Engineering the spin ensemble to act as a negative-mass or positive-mass oscillator, we demonstrate frequency-dependent quantum noise reduction for measurements at the disparate wavelength. The tunability of the spin ensemble enables targeting quantum noise in a variety of systems with dynamics ranging from kHz to MHz. As an example of broadband quantum noise reduction in the acoustic frequency range, we analyse the applicability of our approach to gravitational-wave detectors (GWDs). Other possible applications include continuous-variable quantum repeaters and distributed quantum sensing.
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In vivo structured illumination ophthalmoscopy demonstration on the human retina using adaptive optics
Lai-Tim, Y., L. M. Mugnier, L. Krafft, A. Chen, C. Petit, P. Mecê, K. Grieve, M. Paques, and S. Meimon
Biomedical Optics Express 16, no. 7, 2923-2944 (2025)
Résumé: Structured illumination microscopy (SIM) is one of the most versatile super-resolution techniques. Yet, its application to high-resolution live imaging has been mainly limited to fluorescent and stationary specimens. Here, we present advancements in SIM to jointly tackle all the challenges of imaging living samples, i.e., obtaining super-resolution over an undistorted wide-field while dealing with sample motion, multiple scattering, sample-induced optical aberrations, and low signal-to-noise ratio. By using adaptive optics to compensate for optical aberrations and a reconstruction algorithm tailored for moving and thick tissue, we successfully apply SIM to in vivo retinal imaging and demonstrate structured illumination ophthalmoscopy with optical sectioning and resolution improvement for in vivo imaging of the human retina.
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Homogenized models of acoustic metainterfaces made of three-dimensional Helmholtz resonators
Tachet, S., K. Pham, and A. Maurel
Proceedings of the Royal Society A Mathematical Physical and Engineering Sciences 481, no. 2316 (2025)
Résumé: We investigate the behaviour of metainterfaces composed of three-dimensional subwavelength Helmholtz resonators (HRs), that are open at both ends and may have distinct neck geometries, using a homogenized model derived from a three-scale asymptotic approach. This model reduces such metainterfaces to homogenized boundary conditions that incorporate a resonant pressure field, providing a continuous representation of the discrete pressure field within the cavities that constitute the metasurface. Notable special cases include mirror-symmetric metainterfaces and metasurfaces that operate solely in reflection. The model, developed in the time domain, is validated and discussed in the harmonic regime through comparisons with direct numerical simulations.
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