A new technological development, the laser driven light source (LDLS), in which a laser excited plasma emits intense
continuum radiation over a wide wavelength range from well below the atmospheric cut-off up to 800 nm, promises to
greatly improve our ability to provide high quality flat-fields for astronomical spectrographs. Its particular strength lies
in the ground-based ultraviolet (UV). We report on tests conducted with a LDLS using FORS2, UVES, X-Shooter and
CRIRES at ESO’s Very Large Telescope (VLT) in August 2013. Comparison with standard calibration sources such as
halogen and deuterium lamps shows that with the LDLS flat-fields with a better balanced dynamic range and excellent
signal to noise ratio can be achieved within short exposure times. This will enable higher quality science at the short
wavelength end of existing spectrographs at the VLT. Furthermore the LDLS provides exceptional stability and long
lifetime as important operational aspects. Optimised UV spectrographs such as the proposed CUBES (wavelength range
300-400 nm) project will be able to take full advantage of this development removing the long-standing limitation of
signal to noise ratios of UV flat-fields.
KEYWORDS: Luminescence, Skin, In vivo imaging, Multispectral imaging, Imaging systems, Molecular imaging, Signal detection, Data acquisition, Visible radiation, Drug discovery
In a previous study, we investigated physical methods to reduce whole-body, diet-related autofluorescence interference in several mouse strains through changes in animal diet. Measurements of mice with an in vivo multispectral imaging system over a 21-day period allowed for the quantification of concentration changes in multiple in vivo fluorophores. To be an effective instrument, a multispectral imaging system requires a priori spectral knowledge, the form and importance of which is not necessarily intuitive, particularly when noninvasive in vivo longitudinal imaging studies are performed. Using an optimized spectral library from a previous autofluorescence-reduction study as a model, we investigated two additional spectral definition techniques to illustrate the results of poor spectral definition in a longitudinal fluorescence imaging study. Here we systematically evaluate these results and show how poor spectral definition can lead to physiologically irrelevant results. This study concludes that the proper selection of robust spectra corresponding to each specific fluorescent molecular label of interest is of integral importance to enable effective use of multispectral imaging techniques in longitudinal fluorescence studies.
A confocal reflectance theta line-scanner is being developed for imaging human tissues in vivo. The theta line scanner design potentially offers a newer alternative to current point scanners that may simplify the optics, electronics and mechanics and lead to smaller, inexpensive confocal microscopes. An oscillating galvanometric mirror directly scans in the pupil of a cylindrical lens and one-half of an objective lens, to produce a focused, scanned line in the object plane within tissue. Backscattered light is collected by the other half of the objective lens and focused onto a linear CMOS detector. The illumination is with a diode laser at 830 nm and imaging with a 10X, 0.8 NA water immersion lens. The illumination and detection paths are thus oriented at an angle (theta) to each other, and are separate everywhere except in the confocal plane. This configuration eliminates back-scattered light from optical components and enhances contrast. Optical design analysis has been verified with experimental results, demonstrating lateral resolution on the order of 1 um and optical sectioning (axial resolution) better than 5 um within living human skin. A Fourier optics-based analytical model is in progress to evaluate line spread functions versus illumination and detection pupil conditions. Nuclear and cellular detail is imaged in the epidermis of human skin in vivo and ex vivo (freshly excised specimens). Such a scanner may prove useful for imaging human tissues in clinical and intra-operative settings.
It has been shown previously that images collected at selected wavelengths in a sufficiently narrow bandwidth can be used to produce maps of the oxygen saturation of hemoglobin in the dermis. A four-wavelength algorithm has been developed based on a two-layer model of the skin, in which the blood is contained in the lower layer (dermis), while the upper layer attenuates some of the reflection and adds a clutter term. In the present work, the algorithm is compared analytically to simpler algorithms using three wavelengths and based on a single-layer model. It is shown through Monte-Carlo models that, for typical skin, the single-layer model is adequate to analyze data from fiber-optical reflectance spectroscopy, but the two-layer model produces better results for imaging systems. Although the model does not address the full complexity of reflectance of a two-layer skin, it has proven to be sufficient to recover the oxygen saturation, and perhaps other medically relevant information. The algorithm is demonstrated on a suction blister, where the epidermis is removed to reveal the underlying dermis. Applications for this imaging modality exist in dermatology, in surgery, and in developing treatment plans for various diseases.
Recent advances in imaging spectroscopy provide the opportunity for mapping the oxygen saturation of blood in skin with high accuracy, large spatial coverage, small spatial resolution, and high update rate. A four-wavelength algorithm, specifically designed to compute the oxygen saturation of hemoglobin, in vivo, from a set of narrow-band visible images was used to analyze various skin tissue disorders. To illustrate the spatial capability of this algorithm, mapping of the oxygen saturation of normal skin, hypoxic tissue and various skin lesions was performed using reflectance spectroscopy, demonstrating the spatial resolution of the images of blood oxygen in the tissues. To explore the accuracy of the algorithm, Monte-Carlo modeling was used to generate reflectivities of skin with known parameters. These reflectivities were used to evaluate the limiting effects of quantization error, photon noise, and finite filter bandwidth on the accuracy of the algorithm. In addition, a signal-to-noise analysis was performed to determine the illumination requirements. It is shown that accurate maps of blood oxygen can be produced with good spatial resolution.
Due to the increasing infromation capacity of optical fibernetworks the need for immediate restoration has become a necessity. The fiber cut or `back-hoe fade' is now a significant factor to network design and implementation. In this paper details of network restoration techniques relying on diverse fiber routing and intelligent optical switches are given.
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