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The Association of Amyloid Plaque Count with a Decrease in the Complexity of the BOLD Signal Observed in Alzheimer's Disease
Get PDFAlzheimer's disease (AD) is a prevalent degenerative disease that is both idiopathic and highly debilitating, calling for early detection and intervention before extensive irreversible brain damage occurs. Here, a novel functional complexity measure based on information theory was applied to mark a disease-related reduction in stochastic low frequency (0.01-0.08 Hz) BOLD signal fluctuations at rest. As AD progresses, BOLD signal complexity is expected to decrease in affected regions, alongside an overall increase in brain amyloid burden.In this study, a retrospective analysis was performed on 18F-AV-45 PET and rs-fMRI data from 65 subjects (30 males, 35 females; mean age ± SD: 74 ± 7.4 years), across four clinical groups (Control, Early Mild Cognitive Impairment (EMCI), MCI, and AD). The regional BOLD signal complexity measures, or transient information (TI) values, were determined from the change in uncertainty of BOLD pattern prediction over time (i.e. block entropy growth rate).The main findings in this study included an expected regional reduction in functional complexity with increasing amyloid burden, as well as an unexpected, albeit non-significant, global increase in functional complexity with increased amyloid burden and disease progression. One third (27 out of 82) of the cortical and subcortical grey matter regions presented a significant (>90% CI) effect of brain amyloid load on BOLD signal complexity, including regions associated with disease-related dysfunction in memory, language processing, attention, behavior, somatosensory functions, and motor functions. With disease diagnosis taken into account, only the EMCI group indicated a decrease in global BOLD signal complexity with increased brain amyloid load.Analysis of rs-BOLD signal complexity has the potential to provide a more accurate representation of disease state than current amyloid plaque or structural measures, as well as identify the regions altered by disease pathology. Based on the reduced signal complexity reported in regions previously linked to disease pathology (precuneus/posterior cingulate, lateral temporal lobe, and frontal regions), further study of this novel metric is advised. With validation, the BOLD complexity analysis metric can be attuned to use as a cognitive biomarker in the clinical setting, potentially improving disease diagnosis, treatment monitoring, and evaluation of future treatment options
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Statistical Shape Analysis on MRI
Get PDFMedical imaging including magnetic resonance imaging (MRI) has become a major source of information for making clinical decisions, specifically based on static and dynamic shape variations of organs and moving structures respectively. Most conventional algorithms for shape extraction from images rely on deterministic modeling that offers no quantification for confidence of the extracted shapes. In this thesis a probabilistic approach for shape extraction is tested that provides a degree of confidence in extracted shapes. The degree of confidence create the important information in clinical decisions. This novel method, termed probabilistic Bayesian shape analysis introduced by Le.T and Schuff.N in [1], utilizes Curvelet transformation and Hidden Markov model simultaneously to detect probabilistic distributions of shape contours. In addition, this thesis, aims to effectively summarize probabilistic shape features in terms of information theoretic measures, such as the entropy (E) and statistical complexity (SC). The approach was initially demonstrated on well-defined hand gestures. To show the clinical potential of probabilistic shape feature extraction, the novel method was tested on tongue shape variations during pronunciation of vowels. Probabilistic shape analysis of tongue movement during vowel pronunciations mapped on MRI was performed on 5 subjects [1 woman, 4 men, age range 25-58], who speak English. MRI consisted of a Fast Low Angle Shot sequence [2]. All subjects were asked to sequentially pronounce the vowels [u:], [i:], [a:], [ae:], [e:], [o:], each for approximately 7 seconds, while having the fast MRI scan of the tongue. A probabilistic contour of tongue shape was extracted from each MRI frame (total = 210) and its features were summarized in terms of E and SC. Variations in E and SC as a function of vowel were then tested using univariate linear mixed effects regression. In addition, a multivariate linear mixed effects regression based on Monte Carlo sampling was used to test variations in E and SC simultaneously. First, the analysis showed that the novel method significantly captures variations in tongue shapes compared to repeated MRI variations. Second, the analysis demonstrated that entropy of the tongue extracted consistent shapes for the vowels [u:], [ae:], and [o:] across subjects, and for SC consistent features were found for [u:], [ae:], [a:] and [o:]. Moreover, using E and SC together capture consistent features for the vowels [a:], [e:], [i:] and [u:] across subjects. In conclusion, this thesis illustrated that the probabilistic shape model captures tongue shapes associated with vowel pronunciation. The new method is of potential interest to clinical studies of tongue disorders and function, including speech therapy, assessment of tongue surgery and assessment of functionality of the tongue. Beyond the tongue, the novel probabilistic approach has potentially wide clinical applications in almost any medical field that uses imaging. Examples of applications for the importance of contour extraction and shape detection include the delineation of almost any organ, such as the shape of kidneys and liver, the changing shapes of tendons in joints during movement, the tracking of change in structure of the beating heart and the shape of a tumor, specifically in the brain
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
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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