Исследование спектрально- кинетических характеристик люминофоров переменного состава на основе алюмоиттриевого граната

В процессе исследования проводились сбор, обработка и систематизация литературных данных об основных характеристиках, предъявляемых к люминофорам для светодиодов белого свечения, освоена методика измерения спектрально – кинетических характеристик люминофоров, проведен экономический анализ работы, также были определены мероприятия по технике безопасности. В результате исследования были получены экспериментальные результаты спектрально – кинетических характеристик исследуемых люминофоров переменного состава, сделаны выводы о влиянии концентрации спекающей добавки в составе люминофора.Nowadays,YAG:Ce3+ phosphors are the most widely used yellow LED because of its appropriate spectral property. The research of this work is to study the influence of the flux on the morphology of the YAG phosphors particles. As a result, the spectral and kinetic characteristics of the YAG:Ce3+ phosphors of variable composition were obtained

A finite element method model to simulate laser interstitial thermo therapy in anatomical inhomogeneous regions

BACKGROUND: Laser Interstitial ThermoTherapy (LITT) is a well established surgical method. The use of LITT is so far limited to homogeneous tissues, e.g. the liver. One of the reasons is the limited capability of existing treatment planning models to calculate accurately the damage zone. The treatment planning in inhomogeneous tissues, especially of regions near main vessels, poses still a challenge. In order to extend the application of LITT to a wider range of anatomical regions new simulation methods are needed. The model described with this article enables efficient simulation for predicting damaged tissue as a basis for a future laser-surgical planning system. Previously we described the dependency of the model on geometry. With the presented paper including two video files we focus on the methodological, physical and mathematical background of the model. METHODS: In contrast to previous simulation attempts, our model is based on finite element method (FEM). We propose the use of LITT, in sensitive areas such as the neck region to treat tumours in lymph node with dimensions of 0.5 cm – 2 cm in diameter near the carotid artery. Our model is based on calculations describing the light distribution using the diffusion approximation of the transport theory; the temperature rise using the bioheat equation, including the effect of microperfusion in tissue to determine the extent of thermal damage; and the dependency of thermal and optical properties on the temperature and the injury. Injury is estimated using a damage integral. To check our model we performed a first in vitro experiment on porcine muscle tissue. RESULTS: We performed the derivation of the geometry from 3D ultrasound data and show for this proposed geometry the energy distribution, the heat elevation, and the damage zone. Further on, we perform a comparison with the in-vitro experiment. The calculation shows an error of 5% in the x-axis parallel to the blood vessel. CONCLUSIONS: The FEM technique proposed can overcome limitations of other methods and enables an efficient simulation for predicting the damage zone induced using LITT. Our calculations show clearly that major vessels would not be damaged. The area/volume of the damaged zone calculated from both simulation and in-vitro experiment fits well and the deviation is small. One of the main reasons for the deviation is the lack of accurate values of the tissue optical properties. In further experiments this needs to be validated

Spectroscopic-speckle variance OCT for microvasculature detection and analysis

We propose and studied optical coherence tomography (OCT) combining spectroscopic (SOCT) and speckle variance (svOCT) functions to effectively detect locations of microvasculatures and assess blood oxygen saturation level. Chorioallantoic membrane of a chick embryo was imaged in vivo to perform the analysis of the system. We also studied the effect of speckle in spectral domain using experimental data and performed time-averaging to reduce speckle noise locally. We combined SOCT and svOCT images using hue, saturation and value (HSV) color map to show the localized spectroscopic property of blood. Results show distinct spectroscopic properties between arterial blood and capillary blood

UNRAVELING ASTROCYTE BEHAVIOUR IN THE SPACE BRAIN: RADIATION RESPONSE OF PRIMARY ASTROCYTES

Exposure to ionizing radiation as part of space radiation, is a major limiting factor for crewed space exploration. Astronauts will encounter different types of space radiation, which may cause cognitive damage causing detrimental effects on learning and attention, elevated anxiety and depression. Due to its limited regenerative potential, especially the central nervous system (CNS) is very vulnerable towards radiation-induced damage. Astrocytes, the most abundant glial cells of the CNS, have different crucial functions in the CNS, e.g. maintaining normal brain function. In this work, the response of astrocytes towards low linear energy transfer (LET) X-rays and high-LET carbon ions was compared to unravel possible specific effects of space-relevant high-LET radiation. [...

Shedding light on the variability of optical skin properties: finding a path towards more accurate prediction of light propagation in human cutaneous compartments

YesFinding a path towards a more accurate prediction of light propagation in human skin remains an aspiration of biomedical scientists working on cutaneous applications both for diagnostic and therapeutic reasons. The objective of this study was to investigate variability of the optical properties of human skin compartments reported in literature, to explore the underlying rational of this variability and to propose a dataset of values, to better represent an in vivo case and recommend a solution towards a more accurate prediction of light propagation through cutaneous compartments. To achieve this, we undertook a novel, logical yet simple approach. We first reviewed scientific articles published between 1981 and 2013 that reported on skin optical properties, to reveal the spread in the reported quantitative values. We found variations of up to 100-fold. Then we extracted the most trust-worthy datasets guided by a rule that the spectral properties should reflect the specific biochemical composition of each of the skin layers. This resulted in the narrowing of the spread in the calculated photon densities to 6-fold. We conclude with a recommendation to use the identified most robust datasets when estimating light propagation in human skin using Monte Carlo simulations. Alternatively, otherwise follow our proposed strategy to screen any new datasets to determine their biological relevance.European Marie-Curie Actions Programme, Grant agreement no. 60788

Tissue-mimicking phantoms for photoacoustic and ultrasonic imaging

In both photoacoustic (PA) and ultrasonic (US) imaging, overall image quality is influenced by the optical and acoustical properties of the medium. Consequently, with the increased use of combined PA and US (PAUS) imaging in preclinical and clinical applications, the ability to provide phantoms that are capable of mimicking desired properties of soft tissues is critical. To this end, gelatin-based phantoms were constructed with various additives to provide realistic acoustic and optical properties. Forty-micron, spherical silica particles were used to induce acoustic scattering, Intralipid® 20% IV fat emulsion was employed to enhance optical scattering and ultrasonic attenuation, while India Ink, Direct Red 81, and Evans blue dyes were utilized to achieve optical absorption typical of soft tissues. The following parameters were then measured in each phantom formulation: speed of sound, acoustic attenuation (from 6 to 22 MHz), acoustic backscatter coefficient (from 6 to 22 MHz), optical absorption (from 400 nm to 1300 nm), and optical scattering (from 400 nm to 1300 nm). Results from these measurements were then compared to similar measurements, which are offered by the literature, for various soft tissue types. Based on these comparisons, it was shown that a reasonably accurate tissue-mimicking phantom could be constructed using a gelatin base with the aforementioned additives. Thus, it is possible to construct a phantom that mimics specific tissue acoustical and/or optical properties for the purpose of PAUS imaging studies

Heat conduction from the exceedingly hot fiber tip contributes to the endovenous laser ablation of varicose veins

Lower-extremity venous insufficiency is a common condition, associated with considerable health care costs. Endovenous laser ablation is increasingly used as therapy, but its mechanism of action is insufficiently understood. Here, direct absorption of the laser light, collapsing steam bubbles and direct fiber-wall contact have all been mentioned as contributing mechanisms. Because fiber tips have reported temperatures of 800-1,300°C during endovenous laser ablation, we sought to assess whether heat conduction from the hot tip could cause irreversible thermal injury to the venous wall. We approximated the hot fiber tip as a sphere with diameter equal to the fiber diameter, having a steady state temperature of 800°C or 1,000°C. We computed venous wall temperatures due to heat conduction from this hot sphere, varying the pullback velocity of the fiber and the diameter of the vein. Venous wall temperatures corresponding to irreversible injury resulted for a 3 mm diameter vein and pullback velocities <3 mm/s but not for 5 mm and 1 mm/s. The highest wall temperature corresponded to the position on the wall closest to the fiber tip, hence it moves longitudinally in parallel with the moving fiber tip. We concluded that heat conduction from the hot fiber tip is a contributing mechanism in endovenous laser ablation

Effect of the size and shape of a red blood cell on elastic light scattering properties at the single-cell level

We demonstrate the use of a double-beam optical tweezers system to stabilize red blood cell (RBC) orientation in the optical tweezers during measurements of elastic light scattering from the trapped cells in an angle range of 5-30 degrees. Another laser (He-Ne) was used to illuminate the cell and elastic light scattering distribution from the single cell was measured with a goniometer and a photomultiplier tube. Moreover, CCD camera images of RBCs with and without laser illumination are presented as complementary information. Light scattering from a RBC was measured in different fixed orientations. Light scattering from cells was also measured when the length of the cell was changed in two different orientations. Light scattering measurements from spherical and crenate RBCs are described and the results are compared with other cell orientations. Analysis shows that the measured elastic light scattering distributions reveal changes in the RBC’s orientation and shape. The effect of stretching on the changes in scattering is larger in the case of face-on incidence of He-Ne laser light than in rim-on incidence. The scattering patterns from RBCs in different orientations as well as from a spherical RBC were compared with numerical results found in literature. Good correlation was found