1,720,977 research outputs found
Tools and methods for low-field MR imaging and elastography
Full text linkLow-field magnetic resonance imaging (MRI) consists in performing MRI using relatively low-strength magnets (< 0.3 T) compared to the common clinical MR scanners (1.5 T - 3 T). Thanks to this feature, “low field” represents a different paradigm with respect to the conventional diagnostic workflow in human healthcare, which is currently constrained to specific radiology department environments in a hospital with fixed, large, yet mostly claustrophobic, expensive high-field MRI scanners requiring careful safety considerations when approaching them.
In fact, the lower magnetic field strength provides opportunities for small, compact, and mobile MR scanners, with reduced siting requirements and overall lower costs, which makes low-field MRI usage possible in settings that cannot be achieved by conventional scanners (such as a physician’s office, intensive-care units, or low-resource areas). Low-field MRI does not aim to compete with but rather to complement standard MR approaches and enable simpler, more efficient, or innovative use cases, such as organ-dedicated scanners, image-guided interventions, or imaging in conditions that would lead to severe susceptibility artifacts in stronger magnets (e.g. body parts containing ferromagnetic implants, organs with iron overload, lungs), as well as improved patient experience.
Recently, research and industrial groups have turned their attention to such long-neglected low-field opportunities after a long trend of MRI development with increased magnetic field strengths. Despite recent general technological advancements, low-field MRI is challenging because of the underlying MR physics: the magnetization of spins inside the body originating from the scanner’s main magnetic field is lower in a low-strength magnet, and the detected MR signal is consequently lower as well. If this signal is not sufficiently high with respect to the acquired noise, as represented by the signal-to-noise ratio (SNR), MRI scans may require diagnostically unfavorable compromises, such as longer duration or coarser image resolution. The main goal of low-field developments is thus to find all the possible means for improving SNR to keep scan time reasonably short for patient compliance and steadiness and to provide an image resolution suitable for the envisioned applications.
The present manuscript describes part of the PhD work at the Center for Adaptable MRI Technology focused on the development of efficient tools and methods for a non-commercial compact 0.1 T MRI scanner for human extremities. In particular, the described work includes the exploration of high-performance detectors for such a system, that would be capable of providing high SNR in the operating regime of a low magnetic field while remaining partially or entirely open (contrary to commonly used closed geometries). Together with the available scanner’s open access, such a feature can enable versatile imaging of variously flexed human extremities and the possibility of access with interventional tools for image-guided operations. This goal has been addressed first by optimizing a biplanar volume detector geometry with full three-side access, and then by integrating such a design into a quadrature detection configuration, where the combination of two decoupled acquisition channels provided an SNR gain of √2 factor. With such a high-performance detector and appropriately implemented MRI sequences, fine-resolution anatomical 3D images of a human ankle and elbow in flexed positions were successfully acquired in less than 10 minutes.
In parallel to the detector investigation, this PhD addressed the development of methods for MR elastography at low field. This advanced technique can estimate the mechanical properties of body tissues non-invasively, similar to manual palpation, to assess different pathological conditions that lead to changes of these properties, such as liver fibrosis or muscle atrophy. Low-field MR elastography can be potentially useful to perform such measurements when high-field scanner techniques fail or are not accurate due to artifacts or signal loss caused by iron accumulation in the organs or ferromagnetic implants proximity. However, no commercial elastography tools exist for low-field MRI systems, and their development in this setting has to tackle the severe constraints of elastography scans to avoid long acquisition times and poor SNR. On the one hand, this PhD investigated approaches for the evaluation of accuracy and reliability of MR elastography pipelines using numerical simulations and experimental acquisitions in a clinical scanner on a heterogeneous phantom made of silicone material with rheometric characterization. On the other hand, such phantoms were employed to develop custom tools and methods for low-field MR elastography. For this purpose, an innovative accelerated 3D acquisition strategy has been proposed to acquire the motion information of waves inside the body that are induced to perform MR elastography. Using the open quadrature detector, this approach allowed short scan times (<3 minutes) in human arms at 0.1 T, and thus, for the first time, it made in vivo MR elastography possible at magnetic fields lower than 1.5 T
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
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
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
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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