1,721,055 research outputs found
Deciphering morpho-functional stroke repercussions on the cortical microvasculature with Bessel beam OCM
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Measuring the thickness of the peritoneal membrane in mice with optical coherence tomography
No full textThe detection and diagnosis of diseases have improved in recent years. Developments in diagnostic techniques have helped to improve treatment in the early stages and to avoid many risks to patients. One such technique is optical coherence tomography (OCT), which is used in many medical applications to perform internal microstructural imaging of the human body at high resolution (typically 10 μm), at high speed and in real time. OCT is non-invasive and can be used as a contact or non-contact technique to obtain an image. In medicine, there are many applications that involve OCT, such as in ophthalmology, gastroenterology, cardiology and oncology. This work demonstrates the use of an OCT system incorporating a swept laser source with a high sweep rate of 16 kHz over a wide range of wavelengths (1260 nm to 1390 nm) to measure the thickness of the peritoneal membrane in mice of different sizes and weights. The real axial line speed is limited by the source that is used in the OCT system. The optical source has a bandwidth of ▵λ =110 nm, centred at λ0 =1325 nm. The aim of this study is to investigate the thickening of the peritoneal membrane which can occur during prolonged peritoneal dialysis in mice. As part of this preliminary study, healthy mice of different weights were euthanized and the thickness of the peritoneal membrane was measured using OCT. The aim was to gather data on the expected range of thicknesses present in healthy animals for future studies. For this work, two locations on the peritoneal membrane of each of 20 mice were imaged
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Optical coherence tomography angiography for chronic venous insufficiency and venous leg ulcer
Full text linkChronic venous insufficiency (CVI) ranks among the most common health care issues worldwide. The current diagnosis of CVI is done by clinical examination and duplex ultrasound, which can only detect visible physical changes and deeper vascular structures whereas the superficial cutaneous vasculature cannot be resolved. There is indeed a lack of information that can potentially be extracted from the cutaneous microvasculature of patients affected by CVI. In this work, we designed and applied an optical coherence tomography angiography (OCTA) system, which is customized for
lower extremity imaging of patients. Featuring fast imaging speed, large field of view, high spatial resolution, and most importantly non-invasiveness, this OCTA system was successfully applied in CVI and venous leg ulcer patient imaging. Using the OCTA results acquired from a cohort of 27 human subjects, we can clearly distinguish the vascular patterns uniquely associated with various stages of CVI. The findings of this study give an unexplored indicator to the disease of CVI and venous leg ulcer. With more patients to be recruited, we believe that OCTA imaging results for CVI can be
used as a powerful tool in CVI screening and diagnosis
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Phase-locked Fourier domain optical coherence tomography
No full textFourier or spectral domain optical coherence tomography (FDOCT) is a multi-dimensional interferometric imaging modality that has attracted increasing interest during the last few years. The reason is its outstanding sensitivity allowing high speed 2D and 3D imaging of weakly backscattering biological tissues in vivo and with high axial resolution. FDOCT has today largely replaced the preceding time domain OCT due to its marked advantage in sensitivity and acquisition speed. In particular, for fast in vivo retinal imaging with high resolution in 3D, FDOCT has become the method of choice. Recent developments enhance the clinical and biomedical potential of FDOCT by aiming from purely structural to functional tissue imaging, revealing tissue dynamics and physiology. The imaging parameter space is becoming highly multi-dimensional by including polarization, Doppler flow and spectroscopy. Two operating modes of FDOCT exist: spectrometer-based and swept-source. The latter captivates with its unprecedented depth-scan speed of several 100kHz whereas the spectrometer-based FDOCT offers ultra-high axial resolution capabilities of 2µm or even better. However, there are drawbacks to both FDOCT modalities including the depth-dependent sensitivity decay as well as the complex ambiguity of the FDOCT signal which leads to disturbing mirror structures as well as a restricted maximum depth range. Phase shifting techniques allow reconstruction of the complex sample signal, resolving the complex ambiguities, therefore reducing these drawbacks considerably. In addition, in the spectrometer-based FDOCT, any sample movement during camera integration causes a blurring of the interference fringes and thus reduces the sensitivity for flow detection. However, information on flow is especially interesting in ophthalmology since several studies of retinal blood flow – using laser Doppler flowmetry – have already outlined that vessel flow properties are early indicators of retinal pathologies like glaucoma, diabetic retinopathy or age related macula degeneration. This thesis proposes two new spectrometer-based FDOCT modalities, both based on the phase-sensitive nature of OCT. Appropriate locking of acquisition speed, exposure time and triggering onto artificially provoked signal phase changes allows the technique to benefit from additional degrees of freedom in the signal detection. The various established models were experimentally verified on biological and technical samples. First, spectrometer-based heterodyne FDOCT, without chromatic phase-shifting errors, was presented and discussed. The achromatic phase-shifting is achieved by using acousto-optic frequency shifters (AOFS). In vivo measurements showed experimentally the suppression of FDOCT-inherent artifacts like complex mirror terms due to the full complex signal reconstruction by quadrature detection of a stable beating frequency at 20'000 depth-scans per second using integrating buckets. In the search for ultra-high axial resolution, the currently available AOFS used were found to be a limiting factor and so further AOFS were developed to provide truly broadband devices. A dual beam extension allowed phase sensitive measurements even through long probing fibers. Phase stability issues with respect to the complex signal reconstruction algorithms used were discussed and it was shown theoretically, and verified experimentally, that amplitude errors are equally disturbing as phase errors. Second, a novel FDOCT modality called resonant Doppler FDOCT was introduced preventing interference fringe blurring caused by moving structures such as flow. The proposed method overcomes this problem by phase-matching the interferometer reference signal to the sample motion by means of an electro-optic phase modulator. Extraction of in vivo blood flow in 3D on a purely intensity basis with an improved velocity range as compared to currently performed color Doppler FDOCT was shown. In addition, for this proposed method, the detectable velocity range is independent of the detector speed. Quantitative flow detection was demonstrated with the same method.LO
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Detection of purkinje images for automatic positioning of fixation target and interferometric measurements of anterior eye chamber
No full textIn cataract surgery, the eye’s natural lens is removed because it has gone opaque and doesn’t allow clear vision any longer. To maintain the eye’s optical power, a new artificial lens must be inserted. Called Intraocular Lens (IOL), it needs to be modelled in order to have the correct refractive power to substitute the natural lens.
Calculating the refractive power of this substitution lens requires precise anterior eye chamber measurements. An interferometry equipment, the AC Master from Zeiss Meditec, AG, was in use for half a year to perform these measurements. A Low Coherence Interferometry (LCI) measurement beam is aligned with the eye’s optical axis, for precise measurements of anterior eye chamber distances. The eye follows a fixation target in order to make the visual axis align with the optical axis. Performance problems occurred, however, at this step. Therefore, there was a necessity to develop a new procedure that ensures better alignment between the eye’s visual and optical axes, allowing a more user friendly and versatile procedure, and eventually automatizing the whole process.
With this instrument, the alignment between the eye’s optical and visual axes is detected when Purkinje reflections I and III are overlapped, as the eye follows a fixation target.
In this project, image analysis is used to detect these Purkinje reflections’ positions, eventually automatically detecting when they overlap.
Automatic detection of the third Purkinje reflection of an eye following a fixation target
is possible with some restrictions. Each pair of detected third Purkinje reflections is used in automatically calculating an acceptable starting position for the fixation target, required for precise measurements of anterior eye chamber distances
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