1,721,269 research outputs found
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
Magnetische versus manuelle Navigation in der interventionellen Neuroradiologie : In-vitro-Ergebnisse
No full textIntroduction: Standard microguidewires used in interventional neuroradiology have a predefined shape of the tip that cannot be changed while the guidewire is in the vessel. We evaluated a novel magnetic navigation system (MNS) that generates a magnetic field to control the deflection of a microguidewire that can be used to reshape the guidewire tip in vivo without removing the wire from the body, thereby potentially facilitating navigation along tortuous paths or multiple acute curves. Method: The MNS consists of two permanent magnets positioned on either side of the fluoroscopy table that create a constant precisely controlled magnetic field in the defined region of interest. This field enables omnidirectional rotation of a 0.014- inch magnetic microguidewire (MG). Speed of navigation, accuracy in a tortuous vessel anatomy and the potential for navigating into in vitro aneurysms were tested by four investigators with differing experience in neurointervention and compared to navigation with a standard, manually controlled microguidewire (SG). Results: Navigation using MG was faster (P=0.0056) and more accurate (0.2 mistakes per trial vs. 2.6 mistakes per trial) only in less-experienced investigators. There were no statistically significant differences between the MG and the SG in the hands of experienced investigators. One aneurysm with an acute angulation from the carrier vessel could be navigated only with the MG while the SG failed, even after multiple reshaping manoeuvres. Conclusion: Our findings suggest that magnetic navigation seems to be easier, more accurate and faster in the hands of less-experienced investigators. We consider that the features of the MNS may improve the efficacy and safety of challenging neurointerventional procedures
Vergleich verschiedener endovaskulärer Platinspiral-Embolisationsverfahren zur Therapie zerebraler Aneurysmen : tierexperimentelle Untersuchungen
No full textOne of the main causes of spontaneous subarachnoid hemorrhage is the rupture of a cerebral aneurysm situated in the Circulus arteriosus Willisii. Treatment options of ruptured cerebral aneurysms include surgical clipping and endovascular therapies. Endovascular methods, especially coiling became an important alternative to the surgical procedure. The configuration of the aneurysm plays an important role to choose which method is best suited for an individual patient. Problems for endovascular therapies can occur in aneurysms with a wide neck. In these cases, parts of the coil loops can protrude into the parent artery and can become a permanent source of embolisms. Another problem is coil compaction with subsequent growing of a new aneurysm neck. In contrast, the surgical method leads to continuous and stable aneurysm obliteration with reconstruction of the vessel wall. Despite these theoretical considerations, clinical data from a recent large prospective study (International Subarachnoid Trial) point toward a better short-term outcome of endovascular treated aneurysms if both the neurosurgeon and the neuroradiologist think that the given aneurysm can be treated with their respective technique. This study demonstrated significant advantages of the endovascular therapy in regard of morbidity and mortality of the patients. Following recent developments, platinum coils were enhanced with different material laminations and coatings to overcome the still present limitations that were outlined above. The objective of this study is to test in an animal model two newly developed types of coated coils, a) coils coated with a bioabsorbable polymer, so called Matrix coils and, b) hydrogel coated coils, so called Hydro coils that increase their volume and lead to a smooth surface. Following treatment, animals were followed over a period of six months and compared to animals treated with conventional platinum coils (GDC-coils), in order to obtain information about reconstruction of the vessel wall and complete and stable obliteration of the aneurysms. Aneurysms were created in 20 rabbits by intraluminal elastase incubation of the common carotid artery. Five animals each were assigned to the following groups: untreated, coils, matrix coils and hydro coils. After the observation period of 6 month digital subtraction angiography (DSA) was performed. Thereafter the animals were euthanized. Angiography, histological examinations and scanning electron microscopy were used for evaluation. In the untreated group all five aneurysms remained patent for the investigated time of 6 month. The group treated with the GDC-coils demonstrated the well known problems of coil compaction and recanalisation, no aneurysm was completely occluded. From a histological point of view, the Matrix coils gave no evidence of complete aneurysms obliteration, however, an increased intra aneurysmatic reaction of the collagenous tissue was documented. Still, an endothelialization as an indication of vascular remodelling was absent in most cases. Only the group treated with Hydro coils gave evidence of completely obliterated aneurysms. Continuous endothelial lining was detected using scanning electron microscopy and histological analysis. Despite some problems and limitations of this experiment, e.g. the small number of animals per group and the follow-up period of only 6 month, it was possible to find consistent results. Hydro coils lead to a completely and stable aneurysm obliteration, whereas the Matrix coils did not show a complete aneurysm obliteration. In case of the Hydro coils it seems that a new embolisation material has emerged which has the known benefits of endovascular treatments over surgical procedures, as being shown in the ISAT-study, and, that, in addition, leads to a complete and stable aneurysm obliteration combined with a remodelling of the vessel wall. Nevertheless, this progress and the development of new materials and techniques should be observed critically and attentively as it has been pointed out that Hydrogel coating may lead to hydrocephalus in the clinical setting. The long-term results in patients will be of particular interest. These should be clarified in enduring clinical trials. Generally speaking the question, if a neuroradiological or interventionell approach is chosen, is depending on the individual case. A well-rehearsed and adapted team of neuroradiologists and neurosurgeons should clarify this, in order to offer an individual and interdisciplinary treatment concept to the patient
Magnetische versus manuelle Navigation in der interventionellen Neuroradiologie : In-vitro-Ergebnisse
No full textIntroduction: Standard microguidewires used in interventional neuroradiology have a predefined shape of the tip that cannot be changed while the guidewire is in the vessel. We evaluated a novel magnetic navigation system (MNS) that generates a magnetic field to control the deflection of a microguidewire that can be used to reshape the guidewire tip in vivo without removing the wire from the body, thereby potentially facilitating navigation along tortuous paths or multiple acute curves. Method: The MNS consists of two permanent magnets positioned on either side of the fluoroscopy table that create a constant precisely controlled magnetic field in the defined region of interest. This field enables omnidirectional rotation of a 0.014- inch magnetic microguidewire (MG). Speed of navigation, accuracy in a tortuous vessel anatomy and the potential for navigating into in vitro aneurysms were tested by four investigators with differing experience in neurointervention and compared to navigation with a standard, manually controlled microguidewire (SG). Results: Navigation using MG was faster (P=0.0056) and more accurate (0.2 mistakes per trial vs. 2.6 mistakes per trial) only in less-experienced investigators. There were no statistically significant differences between the MG and the SG in the hands of experienced investigators. One aneurysm with an acute angulation from the carrier vessel could be navigated only with the MG while the SG failed, even after multiple reshaping manoeuvres. Conclusion: Our findings suggest that magnetic navigation seems to be easier, more accurate and faster in the hands of less-experienced investigators. We consider that the features of the MNS may improve the efficacy and safety of challenging neurointerventional procedures
Vergleich verschiedener endovaskulärer Platinspiral-Embolisationsverfahren zur Therapie zerebraler Aneurysmen : tierexperimentelle Untersuchungen
No full textOne of the main causes of spontaneous subarachnoid hemorrhage is the rupture of a cerebral aneurysm situated in the Circulus arteriosus Willisii. Treatment options of ruptured cerebral aneurysms include surgical clipping and endovascular therapies. Endovascular methods, especially coiling became an important alternative to the surgical procedure. The configuration of the aneurysm plays an important role to choose which method is best suited for an individual patient. Problems for endovascular therapies can occur in aneurysms with a wide neck. In these cases, parts of the coil loops can protrude into the parent artery and can become a permanent source of embolisms. Another problem is coil compaction with subsequent growing of a new aneurysm neck. In contrast, the surgical method leads to continuous and stable aneurysm obliteration with reconstruction of the vessel wall. Despite these theoretical considerations, clinical data from a recent large prospective study (International Subarachnoid Trial) point toward a better short-term outcome of endovascular treated aneurysms if both the neurosurgeon and the neuroradiologist think that the given aneurysm can be treated with their respective technique. This study demonstrated significant advantages of the endovascular therapy in regard of morbidity and mortality of the patients. Following recent developments, platinum coils were enhanced with different material laminations and coatings to overcome the still present limitations that were outlined above. The objective of this study is to test in an animal model two newly developed types of coated coils, a) coils coated with a bioabsorbable polymer, so called Matrix coils and, b) hydrogel coated coils, so called Hydro coils that increase their volume and lead to a smooth surface. Following treatment, animals were followed over a period of six months and compared to animals treated with conventional platinum coils (GDC-coils), in order to obtain information about reconstruction of the vessel wall and complete and stable obliteration of the aneurysms. Aneurysms were created in 20 rabbits by intraluminal elastase incubation of the common carotid artery. Five animals each were assigned to the following groups: untreated, coils, matrix coils and hydro coils. After the observation period of 6 month digital subtraction angiography (DSA) was performed. Thereafter the animals were euthanized. Angiography, histological examinations and scanning electron microscopy were used for evaluation. In the untreated group all five aneurysms remained patent for the investigated time of 6 month. The group treated with the GDC-coils demonstrated the well known problems of coil compaction and recanalisation, no aneurysm was completely occluded. From a histological point of view, the Matrix coils gave no evidence of complete aneurysms obliteration, however, an increased intra aneurysmatic reaction of the collagenous tissue was documented. Still, an endothelialization as an indication of vascular remodelling was absent in most cases. Only the group treated with Hydro coils gave evidence of completely obliterated aneurysms. Continuous endothelial lining was detected using scanning electron microscopy and histological analysis. Despite some problems and limitations of this experiment, e.g. the small number of animals per group and the follow-up period of only 6 month, it was possible to find consistent results. Hydro coils lead to a completely and stable aneurysm obliteration, whereas the Matrix coils did not show a complete aneurysm obliteration. In case of the Hydro coils it seems that a new embolisation material has emerged which has the known benefits of endovascular treatments over surgical procedures, as being shown in the ISAT-study, and, that, in addition, leads to a complete and stable aneurysm obliteration combined with a remodelling of the vessel wall. Nevertheless, this progress and the development of new materials and techniques should be observed critically and attentively as it has been pointed out that Hydrogel coating may lead to hydrocephalus in the clinical setting. The long-term results in patients will be of particular interest. These should be clarified in enduring clinical trials. Generally speaking the question, if a neuroradiological or interventionell approach is chosen, is depending on the individual case. A well-rehearsed and adapted team of neuroradiologists and neurosurgeons should clarify this, in order to offer an individual and interdisciplinary treatment concept to the patient
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
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