Polarization Independent Optical Coherence Tomography

Optical coherence tomography (OCT) is a well established imaging modality for high-resolution three-dimensional imaging in clinical settings. While imaging, care must be taken to minimize the imaging artifacts related to the polarization differences between the sample and the reference signals. Current OCT systems adopt complicated mechanisms, such as the use of multiple detectors, polarization-maintaining fibers, polarization controllers to achieve polarization artifacts free sample images. Often the polarization controllers need readjustment which is not suitable for clinical settings. In this work, we demonstrate a simple approach that can minimize the polarization-related artifacts in the OCT systems. Polarization artifact-free images are acquired using two orthogonally polarized reference signals where the orthogonal polarization is achieved using a Faraday mirror. In the current approach, only a single detector is required which makes the current approach compatiblewith swept-source or camera-basedOCT systems. Furthermore, no polarization controllers are used in the system which increases the system stability while minimizing the artifacts related to the sample birefringence, polarization change due to the sample scattering, and polarization change due to the optical fiber movements present in the system

Depth encoded input polarisation independent swept source cross-polarised optical coherence tomography probe

Within the last decades, several studies have been published that prove the benefit of polarisation sensitive optical coherence (psOCT) tomography for the field of biomedical diagnostics. However, polarisation sensitive imaging typically requires careful control of the polarisation state of the input illumination, which leads to bulky and delicate systems. While psOCT provides quantitative information, it is mostly sufficient to analyse the images qualitatively in the field of biomedical diagnostics. Therefore, a reduced form of this technique, cross-polarised optical coherence tomography (cpOCT), moves into the focus of interest that serves to visualise the birefringence properties of a sample. Despite the low requirements for the illumination's polarisation, most of the proposed systems still include complex illumination control mechanisms. Here, we propose a common path probe based endoscopic system with an lateral resolution of 30 µm and a sensitivity of 103 dB comprising a commercially available swept-source OCT system and a free-space module which does not require any polarisation controlling elements. A Faraday mirror substitutes the complex polarisation control apparatus. We demonstrate the independence of the approach from the polarisation state of the light source by monitoring the illumination power in the orthogonal channels while varying the source polarisation. Furthermore, we validate the ability of the system to reveal the birefringence properties of different samples, starting from a quarter-wave plate, since its properties are fully characterised. Additionally, we present imaging results from several tissues to demonstrate its feasibility for the field of biomedical diagnostics

Cross-Polarized Optical Coherence Tomography System with Unpolarized Light

Cross-polarized optical coherence tomography offers improved contrast for samples which can alter the polarization of light when it interacts with the sample. This property has been utilized to screen pathological conditions in several organs. Existing cross-polarized optical coherence tomography systems require several polarization-controlling elements to minimize the optical fiber movement-related image artifacts. In this work, we demonstrate a cross-polarized optical coherence tomography system using unpolarized light and only two quarter-wave plates, which is free from fiber-induced image artifacts. The simplicity of the approach will find many applications in clinical settings

Portable Optical Coherence Elastography System With Flexible and Phase Stable Common Path Optical Fiber Probe

Biomechanical properties drive the functioning of cells and tissue. Measurement of such properties in the clinic is quite challenging, however. Optical coherence elastography is an emerging technique in this field that can measure the biomechanical properties of the tissue. Unfortunately, such systems have been limited to benchtop configuration with limited clinical applications. A truly portable system with a flexible probe that could probe different sample sites with ease is still missing. In this work, we report a portable optical coherence elastography system based on a flexible common path optical fiber probe. The common path approach allows us to reduce the undesired phase noise in the system by an order of magnitude less than the standard non-common path systems. The flexible catheter makes it possible to probe different parts of the body with ease. Being portable, our system can be easily transported to and from the clinic. We tested the efficacy of the system by measuring the mechanical properties of the agar-based tissue phantoms. We also measured the mechanical properties (Young’s Modulus) of the human skin at different sites. The measured values for the agar phantom and the skin were found to be comparable with the previously reported studies. Ultra-high phase stability and flexibility of the probe along with the portability of the whole system makes an ideal combination for the faster clinical adoption of the optical coherence elastography technique

Chromatic Dispersion Based Wide-Band, Fiber-Coupled, Tunable Light Source for Hyperspectral Imaging

Hyperspectral imaging is a powerful label-free imaging technique that provides topological and spectral information at once. In this work, we have designed and characterized a hyperspectral source based on the chromatic dispersion property of off-the-shelf lenses and converted a supercontinuum laser light source into a hyperspectral imaging light source for 490 nm to 900 nm wavelength range with a spectral resolution of 3.5 nm to 18 nm respectively. The potential of the source was demonstrated by imaging two color dots with different absorption bands. Further, we generated the hypercube of the lily ovary and dense connective tissue and measured their spectral signature as a function of wavelength. We also imaged the lower tongue of a healthy volunteer at 540 nm, 630 nm, and white light. Our simple hyperspectral light source design can easily be incorporated in a standard endoscope or microscope to perform hyperspectral imaging

New Measurements of Orbital Period Change in Cygnus X-3

A nonlinear nature of the binary ephemeris of Cygnus X-3 indicates either a change in the orbital period or an apsidal motion of the orbit. We have made extended observations of Cygnus X-3 with the Pointed Proportional Counters (PPCs) of the Indian X-ray Astronomy Experiment (IXAE) during 1999 July 3-13 and October 11-14. Using the data from these observations and the archival data from ROSAT, ASCA, BeppoSAX and RXTE, we have extended the data base for this source. Adding these new arrival time measurements to the published results, we make a comparison between the various possibilities, (a) orbital decay due to mass loss from the system, (b) mass transfer between the stars, and (c) apsidal motion of the orbit due to gravitational interaction between the two components. Orbital decay due to mass loss from the companion star seems to be the most probable scenario.Comment: 7 pages, 4 figures, accepted for publication in A&

A Proposal to Perform High Contrast Imaging of Human Palatine Tonsil with Cross Polarized Optical Coherence Tomography

The palatine tonsils provide the first line of immune defense against foreign pathogens inhaled or ingested. However, a disruption in the epithelial layer within the tonsil crypts can lead to recurrent acute tonsillitis (RAT). Current imaging techniques suffer from poor resolution and contrast and do not allow a classification of the severity of RAT. We have developed a cross-polarized optical coherence tomography system. The system can detect a change in the polarization of the light after the light-tissue interaction. We demonstrate improved resolution and contrast in tonsil imaging with the developed method. Intensity, as well as retardance images of the excised tonsil tissue, were acquired. Features such as crypt epithelium, lymphoid follicles, and dense connective tissue were observed with improved contrast. Cross polarized optical coherence tomography can be a valuable tool in the clinic to evaluate palatine tonsils as it would allow visualizing common tonsil features without the need for any external contrast agent

Design and Development of Site Specific Grape Vineyard Fertilizer Applicator Prototype

402-407The current fertiliser application methods for grape vines are labour intensive and lead to overuse of fertiliser. Frequent rain and vineyard orchard wash over often pollute water sources. Therefore, the right amount and placement of fertiliser can not only improve crop growth but also reduce the risk of chemicals to human health and the environment. To overcome the above problems a site specific fertiliser applicator for grape vineyard with mechanical sensing system was developed. The sensing system was designed to apply fertiliser to the root zone of the plant canopy. An experimental unit was developed to optimise design and operation parameters for fertiliser production per plant. The urea's physical and engineering qualities were determined for metering mechanism design. The average value of bulk density, angle of repose, urea grain diameter, grain weight in single flute measured were 0.759 ± 0.011 gcm−3, 26.22 ± 1.18°, 3.38 ± 0.23 mm, 1.46 ± 0.04 g, respectively. The coefficient of static friction with plywood, galvanised iron and mild steel with painted surface were observed 0.3177 ± 0.0092, 0.2868 ± 0.0077, and 0.3177 ± 0.0092, respectively. For fertiliser given per plant, the effect of exposure length was p < 0.001. The sensor device opens the delivery tube for fertiliser in 0.9–0.95s

Combinatorial approach towards synthesis of 2',3'-dideoxynucleosides and enzyme-catalysed selective hydrolysis of diethyl acetamidomalonate and amides of polyacetoxy aromatic carboxylic acid

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Aldehydes: magnificent acyl equivalents for direct acylation

From the viewpoint of meeting the current green chemistry challenges in chemical synthesis, there is a need to disseminate how the cocktail of acylation and activation can play a pivotal role in affording bioactive acylated products comprising substituted ketone motifs in fewer reaction steps, with higher atom-economy and improved selectivity. In recent years, a significant number of articles employing the title compounds “aldehydes” as magnificent acylation surrogates which are less toxic and widely applicable have been published. This review sheds light on the compounds use for selective acylation of arene, heteroarene and alkyl (sp3, sp2 and sp) C–H bonds by proficient utilization of the C–H activation strategy. Critical insights into selective acylation of diverse moieties for the synthesis of bioactive compounds are presented in this review that will enable academic and industrial researchers to understand the mechanistic aspects involved and fruitfully employ these strategies in designing novel molecules