Ultrasound matrix imaging for 3D transcranial in vivo localization microscopy
Bureau, F., L. Denis, A. Coudert, M. Fink, O. Couture, and A. Aubry
Science Advances 11, no. 31 (2025)
Résumé: Transcranial ultrasound imaging is usually limited by skull-induced attenuation and high-order aberrations. By using contrast agents such as microbubbles in combination with ultrafast imaging, not only can the signal-to-noise ratio be improved, but super-resolution images down to the micrometer scale of the brain vessels can also be obtained. However, ultrasound localization microscopy (ULM) remains affected by wavefront distortions that limit the microbubble detection rate and hamper their localization. In this work, we show how ultrasound matrix imaging, which relies on the prior recording of the reflection matrix, can provide a solution to these fundamental issues. As an experimental proof of concept, an in vivo reconstruction of deep brain microvessels is performed on three anesthetized sheep. The compensation of wave distortions is shown to markedly enhance the contrast and resolution of ULM. This experimental study thus opens up promising perspectives for a transcranial and nonionizing observation of human cerebral microvascular pathologies, such as stroke.
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Quantitative evaluation of methods to analyze motion changes in single-particle experiments
Muñoz-Gil, G., H. Bachimanchi, J. Pineda, B. Midtvedt, G. Fernández-Fernández, B. Requena, Y. Ahsini, S. Asghar, J. Bae, F. J. Barrantes, S. W. B. Bender, C. Cabriel, J. A. Conejero, M. Escoto, X. Feng, R. Haidari, N. S. Hatzakis, Z. Huang, I. Izeddin, H. Jeong, Y. Jiang, J. Kæstel-Hansen, J. Miné-Hattab, R. Ni, J. Park, X. Qu, L. A. Saavedra, H. Sha, N. Sokolovska, Y. Zhang, G. Volpe, M. Lewenstein, R. Metzler, D. Krapf, G. Volpe, and C. Manzo
Nature Communications 16, no. 1 (2025)
Résumé: The analysis of live-cell single-molecule imaging experiments can reveal valuable information about the heterogeneity of transport processes and interactions between cell components. These characteristics are seen as motion changes in the particle trajectories. Despite the existence of multiple approaches to carry out this type of analysis, no objective assessment of these methods has been performed so far. Here, we report the results of a competition to characterize and rank the performance of these methods when analyzing the dynamic behavior of single molecules. To run this competition, we implemented a software library that simulates realistic data corresponding to widespread diffusion and interaction models, both in the form of trajectories and videos obtained in typical experimental conditions. The competition constitutes the first assessment of these methods, providing insights into the current limitations of the field, fostering the development of new approaches, and guiding researchers to identify optimal tools for analyzing their experiments.
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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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