Coherent light scattering from cellular dynamics in living tissues.

This review examines the biological physics of intracellular transport probed by the coherent optics of dynamic light scattering from optically thick living tissues. Cells and their constituents are in constant motion, composed of a broad range of speeds spanning many orders of magnitude that reflect the wide array of functions and mechanisms that maintain cellular health. From the organelle scale of tens of nanometers and upward in size, the motion inside living tissue is actively driven rather than thermal, propelled by the hydrolysis of bioenergetic molecules and the forces of molecular motors. Active transport can mimic the random walks of thermal Brownian motion, but mean-squared displacements are far from thermal equilibrium and can display anomalous diffusion through Lévy or fractional Brownian walks. Despite the average isotropic three-dimensional environment of cells and tissues, active cellular or intracellular transport of single light-scattering objects is often pseudo-one-dimensional, for instance as organelle displacement persists along cytoskeletal tracks or as membranes displace along the normal to cell surfaces, albeit isotropically oriented in three dimensions. Coherent light scattering is a natural tool to characterize such tissue dynamics because persistent directed transport induces Doppler shifts in the scattered light. The many frequency-shifted partial waves from the complex and dynamic media interfere to produce dynamic speckle that reveals tissue-scale processes through speckle contrast imaging and fluctuation spectroscopy. Low-coherence interferometry, dynamic optical coherence tomography, diffusing-wave spectroscopy, diffuse-correlation spectroscopy, differential dynamic microscopy and digital holography offer coherent detection methods that shed light on intracellular processes. In health-care applications, altered states of cellular health and disease display altered cellular motions that imprint on the statistical fluctuations of the scattered light. For instance, the efficacy of medical therapeutics can be monitored by measuring the changes they induce in the Doppler spectra of livingex vivocancer biopsies.

Topical negative pressure wound therapy enhances the local tissue perfusion - A pilot study.

BACKGROUND: Topical negative pressure wound therapy (TNPWT) is a regularly used method in modern wound treatment with a growing and diverse potential for clinical use. So far positive effects on microcirculation have been observed and examined, although precise statements on the underlying mechanism appear unsatisfying. OBJECTIVE: The aim of our study was to extend the understanding of the effect of TNPWT on tissue perfusion and determine the time frame and the extent to which the tissue perfusion changes due to TNPWT. MATERIAL AND METHODS: TNPWT was applied to the anterior thighs of 40 healthy individuals for 30 min, respectively. Before and up to 90 min after the application, measurements of the amount of regional haemoglobin (rHb), capillary venous oxygen saturation (sO2), blood flow (flow) and velocity were conducted with spectrophotometry (combining white light spectrometry and laser Doppler spectroscopy) within two different depths/skin layers. A superficial measuring probe for depths up to 3 mm and a deep measuring probe for up to 7 mm were used. RESULTS: All parameters show significant changes after the intervention compared to baseline measurements. The greater effect was seen superficially. The superficially measured rHb, sO2 and flow showed a significant increase and stayed above the baseline at the end of the protocol. Whereas deeply measured, the rHb initially showed a decrease. The flow and sO2 showed a significant increase up to 60 min after the intervention. CONCLUSION: The application of TNPWT on healthy tissue shows an increase in capillary-venous oxygen saturation and haemoglobin concentration of at least 90 min after intervention. A possible use in clinical practice for preconditioning to enhance wound healing for high-risk patients to develop wound healing disorder, requires further studies to investigate the actual duration of the effect.

Tunable Microcavity-Stabilized Quantum Cascade Laser for Mid-IR High-Resolution Spectroscopy and Sensing.

The need for highly performing and stable methods for mid-IR molecular sensing and metrology pushes towards the development of more and more compact and robust systems. Among the innovative solutions aimed at answering the need for stable mid-IR references are crystalline microresonators, which have recently shown excellent capabilities for frequency stabilization and linewidth narrowing of quantum cascade lasers with compact setups. In this work, we report on the first system for mid-IR high-resolution spectroscopy based on a quantum cascade laser locked to a CaF2 microresonator. Electronic locking narrows the laser linewidth by one order of magnitude and guarantees good stability over long timescales, allowing, at the same time, an easy way for finely tuning the laser frequency over the molecular absorption line. Improvements in terms of resolution and frequency stability of the source are demonstrated by direct sub-Doppler recording of a molecular line.

Resolving Vertical Variations of Horizontal Neutral Winds in Earth's High Latitude Space-Atmosphere Interaction Region (SAIR).

Few remote sensing or in-situ techniques can measure winds in Earth's thermosphere between altitudes of 120 and 200 km. One possible approach within this region uses Doppler spectroscopy of the optical emission from atomic oxygen at 558 nm, although historical approaches have been hindered in the auroral zone because the emission altitude varies dramatically, both across the sky and over time, as a result of changing characteristic energy of auroral precipitation. Thus, a new approach is presented that instead uses this variation as an advantage, to resolve height profiles of the horizontal wind. Emission heights are estimated using the Doppler temperature derived from the 558 nm emission. During periods when the resulting estimates span a wide enough height interval, it is possible to use low order polynomial functions of altitude to model the Doppler shifts observed across the sky and over time, and thus reconstruct height profiles of the horizontal wind components. The technique introduced here is shown to work well provided there are no strong horizontal gradients in the wind field. Conditions satisfying these caveats do occur frequently and the resulting wind profiles validate well when compared to absolute in-situ wind measurements from a rocket-borne chemical release. While both the optical and chemical tracer techniques agreed with each other, they did not agree with the HWM-14 horizontal wind model. Applying this technique to wind measurements near the geomagnetic cusp footprint indicated that cusp-region forcing did not penetrate to atmospheric heights of 240 km or lower.

Changes of perfusion of microvascular free flaps in the head and neck: a prospective clinical study.

Reconstruction with a free flap is routine in head and neck surgery. However, reliable assessment of perfusion can be difficult, so we prospectively evaluated it in 4 types of microvascular free flaps in the oral cavity (n=196) and assessed differences in blood flow by non-invasive monitoring with a laser Doppler flowmetry unit. We measured oxygen saturation, haemoglobin concentration, and velocity on the surface of the flap preoperatively at the donor site, and on the flap on the first, second, and seventh postoperative days, and after 4 weeks in 186/196 patients, mean (SD) age of 60 (13) years. We studied the radial forearm (n=76, 41%), fibular (n=45, 24%), anterolateral thigh (n=53, 28%), and soleus perforator (n=12, 7%) flaps. The values for the radial forearm flap differed significantly from the others. There were significant differences in haemoglobin concentrations between the fibular and soleus perforator flaps, and between the anterolateral thigh and soleus perforator flaps (p=0.002 each). Free flaps are unique in the way that perfusion develops after microvascular anastomoses. Knowledge of how each flap is perfused may indicate different patterns of healing that could potentially influence long term rehabilitation and detection of future deficits in perfusion.