1,721,109 research outputs found
Three-dimensional, static displacement, stimulated echo, magnetic resonance elasticity imaging.
No full textPalpation, or the sense of touch, has long been used by physicians to detect disease. The underlying basis for this detection is the presence of hard tissue. Indeed, direct mechanical measurements suggest that the Young's (or shear) elastic modulus may differ by orders of magnitude within soft tissues in various physiologic states. Although palpation is a powerful diagnostic tool, its sensitivity is relatively poor within deep, dense, or heterogeneous tissue. Thus, most manually detected lesions are either superficial, relatively large, or both. In this work, three-dimensional (3D), static displacement, stimulated echo, magnetic resonance elasticity imaging (EI), a potential method for extending the range and sensitivity of palpation by imaging tissue mechanical properties, is explored. The static, linear, isotropic model used, as well as the physical basis for internal displacement measurement via phase-contrast magnetic resonance imaging (MRI), are discussed. Simulations show that optimal EI data are obtained when the displacement-induced intravoxel phase wrap is pi radians. A theoretical study illustrating the effects of undesired motion on the acquired signal is presented, along with a displacement encoding scheme to reduce these effects and results from a phantom experiment. We hypothesized that 3D EI methods, readily implemented with 3D MRI, would offer advantages over standard two-dimensional (2D) EI techniques. Using both an analytic model and a phantom study, 3D EI is shown to lead to higher geometric and mechanical accuracy than 2D EI. However, such 3D data acquisitions take several hours using standard stimulated echo MRI. To permit clinical 3D EI, a method for rapidly acquiring 3D, T2*-free, displacement-encoded data was developed. Using this technique, the time needed for acquiring a 128 x 128 x 8 displacement map was reduced from over 2 hours to 8 minutes. This reduction comes with a concomitant increase in the average displacement error per voxel from approximately 0.08 to 0.12 mm. Average relative errors in the strain tensor components increased 16--30%. Finally, possible methods for implementing this technique clinically and for expanding the elasticity model used to include nonlinearities and anisotropy are discussed.* *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat.PhDApplied SciencesBiological SciencesBiomedical engineeringBiophysicsHealth and Environmental SciencesMedical imagingUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125562/2/3192836.pd
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
K -space acquisition method for dynamic contrast -enhanced MRI: Application to breast tumors.
No full textDynamic contrast-enhanced (DCE)-MRI is increasingly being used for detection and diagnosis of tumors. The objective of DCE-MRI is to elicit diagnostically significant architectural and pharmacokinetic features of lesions. Hence, DCE-MRI of tumors is ideally performed at high spatial resolution while sampling a time-varying process at high temporal resolution. A variety of variable rate sampling strategies and associated reconstructive schemes have been developed to resolve the conflicting demands of simultaneous high resolution sampling of temporal and spatial detail. In this work a novel method, termed spatio-temporal bandwidth-based (STBB) acquisition, is developed to address the trade-off inherent in DCE-MRI. This technique is constrained only by the overall scan duration, within which the temporal changes are expected to reach steady-state, the imaging sequence repetition time (TR), and a targeted spatio-temporal object. Neither the spatial nor temporal resolution is preselected. The STBB formalism, which is applicable to any dynamic contrast-enhanced imaging condition, is demonstrated using a priori modeling of breast tumors. The k-space traversal scheme is obtained by maximizing energy coverage of the Fourier space that encompasses the instantaneous spectral energy of the temporally enhancing object during the DCE-MRI experiment. A method to use the energy maximization concept in designing an acquisition scheme that is adequate for a class of space-time objects is also demonstrated in this work. This concept was tested in computer simulations under a range of object spatial features and enhancement conditions. In addition, two issues that closely impact the accuracy in quantification of pharmacokinetic parameters measured using DCE-MRI are addressed: motion artifact and B1-field inhomogeneity. A linear three-dimensional motion-correction algorithm to compensate for patient motion over the course of the dynamic acquisition is developed. The errors in parameter estimation due to B1-field inhomogeneity are investigated and a correction method is proposed.PhDApplied SciencesBiomedical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124463/2/3138205.pd
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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