1,721,119 research outputs found
High Resolution 3D Diffusion Kurtosis Imaging of Whole Rat Brain
No full textThis thesis involves the development of an overnight high-resolution 3D diffusion kurtosis imaging protocol for ex vivo whole rat brain imaging. MRI acquisition parameters were optimized in order to obtain high-resolution, high-precision diffusion kurtosis imaging data. This included the programming and development of a 3D diffusion-weighted fast spin-echo pulse sequence. Image data from ex vivo rat brains were collected to verify the efficacy of the imaging protocol. Values of diffusion kurtosis parameters in normal rat brains were similar to those reported in previous imaging studies. Using this protocol, preliminary data were collected from a model of schizophrenia in rats. These data indicated the ability of the protocol to detect changes in diffusion kurtosis parameters that could correlate to changes in white matter microstructure
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
Validation of Quantitative Bound and Pore Water Imaging in Cortical Bone
No full textClinically compatible ultra-short echo time (UTE) imaging sequences for quantitative T2-based bound and pore water imaging in bone were implemented and validated on a 3T human scanner and a 4.7T small bore system. Pore water images were generated by selectively saturating bound water signals with a T2-selective double adiabatic inversion pulse. Bound water images were generated by nulling the pore water signals with a T2-selective adiabatic inversion recovery preparation. In both cases, the magnetization preparation was integrated into a 3D UTE acquisition, with 16 radial spokes acquired per preparation. Images were acquired from human cadaveric femoral mid-shafts, from which isolated bone samples were subsequently extracted for non-imaging analysis using T2 spectroscopic measurements. The results showed a strong correlation between imaging-derived concentrations of bound and pore water and those determined from the isolated bone samples
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
The Information Content of mcDESPOT
No full textA statistical analysis of the magnetic resonance imaging-based mcDESPOT method for characterizing two exchanging water proton pools--a seven-dimensional problem that fits to multiple flip angle measurements of both spoiled and refocused gradient echoes--is presented. Theoretical calculations of the Cramer-Rao lower bounds of the variance of fitted model parameters were made using a variety of model system parameters, meant to mimic those expected in human white matter. The results, validated by Monte Carlo simulations, indicated that mcDESPOT signals acquired at feasibly attainable signal to noise ratios cannot provide parameter estimates with useful levels of precision. Precision can be greatly improved by constraining solutions with a priori model information, although this will generally lead to biased parameter estimates with less specificity. These results indicate that previous, apparently successful applications of mcDESPOT to human white matter may have used data fitting methods that implicitly constrained parameter solutions, or that the two-pool model of white matter may not be sufficient to describe the observed water proton signal in mcDESPOT acquisitions. In either case, mcDESPOT-derived estimates of two-pool model parameters cannot yet be unambiguously related to specific tissue characteristics
Imaging of Osteolytic Breast Cancer Metastases with Computed Tomography, Positron Emission Tomography and Single Photon Emission Computed Tomography
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