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Pulsed photothermal radiometry of port-wine stains
Get PDFThe application of pulsed photothermal radiometry (PPTR) diagnostics to characterize port wine stain (PWS) lesions is discussed. Influence of epidermal absorbance and PWS depth on the PPTR signal is analyzed using an in-vitro model of PWS skin consisting of multilayered collagen films. An instrument is constructed and used for patient and animal model PPTR measurements. When an infrared fiber is incorporated, the instrumentation facilitates convenient skin-site accessibility. Modulation of the PPTR signal and homodyne detection substantially improve the system signal-to-noise ratio over previous methods. Given the measured PPTR signal, an algorithm computes the initial temperature distribution in the PWS skin immediately after the laser pulse. The use and limitations of the algorithm are presented and discussed
Oblique incidence reflectometry: optical-fiber implementation
Get PDFA new, simple and quick approach, oblique-incidence reflectometry, was used to measure the absorption and reduced scattering coefficients of a semi-infinite turbid medium. An obliquely incident light beam causes the center of the far diffuse reflectance to shift from the point of incidence, where the far diffuse reflectance refers to the diffuse reflectance that is several transport mean free paths away from the incident point. The amount of shift yields the diffusion constant by a simple formula, and the slope of the diffuse reflectance yields the attenuation coefficient. Only the relative profile of the diffuse reflectance is needed to deduce both optical parameters, which makes this method attractive in clinical settings because it does not require a stringent calibration for absolute quantity measurements. This method was tested theoretically by Monte Carlo simulations and experimentally by a reflectometer. Because this method can be used to measure optical properties of biological tissues quickly and requires on inexpensive equipment, it has potential clinical application to the diagnosis of disease or monitoring of treatments
Computation of the optical properties of tissues from light reflectance using a neural network
Get PDFWe have established a neural network to quickly deduce optical properties of tissue slabs from the diffuse reflectance distribution. Diffusion theory based on multiple image sources mirrored about the two extrapolated boundaries is used to prepare the training and testing sets for the neural network. The neural network is trained using backpropagation with the conjugate gradient method. Once the neural network is trained, it is able to deduce optical properties of tissues within on the order of a millisecond. The range of the tissue optical properties that is covered by our neural network is 0.01 - 2 cm^(-1) for absorption coefficient, 5 - 25 cm^(-1) for reduced scattering coefficient, and 0.001 - 1 cm for tissue thickness. A separate network is also trained for thick tissue slabs. A simple experimental setup applying the trained neural network is designed to measure tissue optical properties quickly
Animated simulation of light transport in tissues
Get PDFTime-resolved light transport in composite tissues is simulated using the Monte Carlo technique. Snapshots of spatial distributions of physical quantities, including light absorption rate, light fluence rate, and diffuse reflectance rate, are presented. Such multiple snapshots with a given time interval can be shown sequentially to achieve an animation effect. This animated simulation is a tool that aids in the general understanding of light transport in tissues. For example, the simulation of time-resolved spatial distribution of light fluence rate inside a tissue illustrates how fast light is dispersed inside tissues. The simulation of diffuse reflectance rate as a function of time of a short-pulsed laser incident upon a piece of tissue containing a buried object shows that early reflected light does not carry imaging information of the object. The imaging quality of the object can thus be improved by rejecting the early-arriving reflected light
Laser optoacoustic imaging of turbid media: determination of optical properties by comparison with diffusion theory and Monte Carlo simulation
Get PDFLaser optoacoustic imaging based on time-resolved detection of laser-induced thermoelastic pressure waves can be potentially used in medicine as a diagnostic tool (tomography) and as means to measure tissue optical properties in vivo. Information on tissue optical properties in vivo is important for laser dosimetry and tissue characterization. Analysis of the profile and amplitude of laser-induced transient stress can provide direct information about absorbed energy distribution in irradiated volume. Pressure wave profiles exactly correspond to temperature distributions generated in tissues under irradiation conditions of temporal stress confinement. In this study we experimentally measured pressure wave profile and amplitude upon irradiation of highly scattering gel phantoms and aqueous solutions colored with potassium chromate and made turbid with polystyrene spheres. A wide-band lithium niobate acoustic transducer was used to detect laser-induced pressure waves. The experimentally measured laser-induced stress profiles and the results of a Monte Carlo simulation were in excellent agreement. Computer code was developed to calculate separately absorption and scattering coefficients from transient stress profiles. Our study has demonstrated feasibility of time-resolved detection of laser-induced acoustic transients as a method for tissue optical properties measurements in vivo
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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