An adaptive non-local means filter for denoising live-cell images and improving particle detection

Fluorescence imaging of dynamical processes in live cells often results in a low signal-to-noise ratio. We present a novel feature-preserving non-local means approach to denoise such images to improve feature recovery and particle detection. The commonly used non-local means filter is not optimal for noisy biological images containing small features of interest because image noise prevents accurate determination of the correct coefficients for averaging, leading to over-smoothing and other artifacts. Our adaptive method addresses this problem by constructing a particle feature probability image, which is based on Haar-like feature extraction. The particle probability image is then used to improve the estimation of the correct coefficients for averaging. We show that this filter achieves higher peak signal-to-noise ratio in denoised images and has a greater capability in identifying weak particles when applied to synthetic data. We have applied this approach to live-cell images resulting in enhanced detection of end-binding-protein 1 foci on dynamically extending microtubules in photo-sensitive Drosophila tissues. We show that our feature-preserving non-local means filter can reduce the threshold of imaging conditions required to obtain meaningful data

Multi-mode microscopy using diffractive optical elements

This paper discusses a range of phase-diversity and tracking applications that have been demonstrated experimentally, and will present an analysis of experimental errors associated with the system used. Simultaneous imaging in multiple imaging modes is demonstrated and the use of wavefront-sensing techniques to achieve nanometric depth resolution is reviewed

Fermeture de phase en astronomie optique

On envisage des simplifications aux techniques récemment proposées afin d'utiliser la « fermeture de phase » en astronomie optique, techniques visant à obtenir la limite théorique de diffraction en imagerie . La méthode envisagée permet de corriger des images isolées, obtenues à courte exposition et dégradées par la turbulence atmosphérique, jusqu'à la limite de diffraction malgré la traversée de l'atmosphère terrestre . Elle prend toute son importance lorsqu'on l'applique à obtenir des images de haute résolution à partir d'une orbite autour de la Terre sans qu'il soit nécessaire de disposer à bord du satellite d'une surface de haute précision optique sur une grande ouverture . A la base de cette méthode : un interféromètre à pupilles multiples, comportant suffisament de redondances internes pour pouvoir séparer les paramètres de l'objet de ceux de l'instrument, chacun étant déterminé alors sans introduire de modèles a priori . Pour une application spatiale, le champ pourrait être dédoublé au moyen de séparateurs et de retards optiques autorisant des mesures à large bande. Une source de référence permet alors dans l'un des champs la stabilisation active de l'instrument - une précision de 1/100 de longueur d'onde paraît accessible, en étudiant une configuration praticable, sur une étoile de magnitude inférieure a 12 . L'autre champ est alors disponible pour de longues intégrations sur des objects faibles .Simplifications of recently proposed techniques for using phase closure to achieve diffraction-limited imaging in optical astronomy are considered . The technique permits synthesis of diffraction-limited images from single, short-exposure, turbulence-degraded images of bright objects viewed through the earth's atmosphere, but is more important as a method for obtaining high resolution images from earth-orbit without the need to put a single large aperture of accurate figure in space . The basis of the method is a multi-aperture interferometer with sufficient redundancy built into the instrument to permit the separation of instrumental and object dependent parameters and thus to permit each of these to be determined without recourse to model building. By use of image-slicing and optical delay lines it is possible to achieve broad-band imaging in two sub-fields . One of the sub-fields may be used as a reference to "shape lock" the instrument to x ./100 accuracy on a source of magnitude < 12, whilst the other is used to obtain long integrations on faint objects

Nanometric depth resolution from multi-focal images in microscopy

We describe a method for tracking the position of small features in three dimensions from images recorded on a standard microscope with an inexpensive attachment between the microscope and the camera. The depth-measurement accuracy of this method is tested experimentally on a wide-field, inverted microscope and is shown to give approximately 8 nm depth resolution, over a specimen depth of approximately 6 µm, when using a 12-bit charge-coupled device (CCD) camera and very bright but unresolved particles. To assess low-flux limitations a theoretical model is used to derive an analytical expression for the minimum variance bound. The approximations used in the analytical treatment are tested using numerical simulations. It is concluded that approximately 14 nm depth resolution is achievable with flux levels available when tracking fluorescent sources in three dimensions in live-cell biology and that the method is suitable for three-dimensional photo-activated localization microscopy resolution. Sub-nanometre resolution could be achieved with photon-counting techniques at high flux levels

Effects of a high-dose 24-h infusion of tranexamic acid on death and thromboembolic events in patients with acute gastrointestinal bleeding (HALT-IT): an international randomised, double-blind, placebo-controlled trial

Background: Tranexamic acid reduces surgical bleeding and reduces death due to bleeding in patients with trauma. Meta-analyses of small trials show that tranexamic acid might decrease deaths from gastrointestinal bleeding. We aimed to assess the effects of tranexamic acid in patients with gastrointestinal bleeding. Methods: We did an international, multicentre, randomised, placebo-controlled trial in 164 hospitals in 15 countries. Patients were enrolled if the responsible clinician was uncertain whether to use tranexamic acid, were aged above the minimum age considered an adult in their country (either aged 16 years and older or aged 18 years and older), and had significant (defined as at risk of bleeding to death) upper or lower gastrointestinal bleeding. Patients were randomly assigned by selection of a numbered treatment pack from a box containing eight packs that were identical apart from the pack number. Patients received either a loading dose of 1 g tranexamic acid, which was added to 100 mL infusion bag of 0·9% sodium chloride and infused by slow intravenous injection over 10 min, followed by a maintenance dose of 3 g tranexamic acid added to 1 L of any isotonic intravenous solution and infused at 125 mg/h for 24 h, or placebo (sodium chloride 0·9%). Patients, caregivers, and those assessing outcomes were masked to allocation. The primary outcome was death due to bleeding within 5 days of randomisation; analysis excluded patients who received neither dose of the allocated treatment and those for whom outcome data on death were unavailable. This trial was registered with Current Controlled Trials, ISRCTN11225767, and ClinicalTrials.gov, NCT01658124. Findings: Between July 4, 2013, and June 21, 2019, we randomly allocated 12 009 patients to receive tranexamic acid (5994, 49·9%) or matching placebo (6015, 50·1%), of whom 11 952 (99·5%) received the first dose of the allocated treatment. Death due to bleeding within 5 days of randomisation occurred in 222 (4%) of 5956 patients in the tranexamic acid group and in 226 (4%) of 5981 patients in the placebo group (risk ratio [RR] 0·99, 95% CI 0·82–1·18). Arterial thromboembolic events (myocardial infarction or stroke) were similar in the tranexamic acid group and placebo group (42 [0·7%] of 5952 vs 46 [0·8%] of 5977; 0·92; 0·60 to 1·39). Venous thromboembolic events (deep vein thrombosis or pulmonary embolism) were higher in tranexamic acid group than in the placebo group (48 [0·8%] of 5952 vs 26 [0·4%] of 5977; RR 1·85; 95% CI 1·15 to 2·98). Interpretation: We found that tranexamic acid did not reduce death from gastrointestinal bleeding. On the basis of our results, tranexamic acid should not be used for the treatment of gastrointestinal bleeding outside the context of a randomised trial