1,721,002 research outputs found
Cerebral infarcts and cerebrovascular disease in neurologically intact Tanzanian children with sickle cell anaemia
No full textIntroduction:Children and adolescents with sickle cell anemia (SCA) without history of neurological manifestations remain at risk of stroke and require cost effective screening as evidence-based stroke prevention interventions are developed. Although there are data on the prevalence of Transcranial Doppler (TCD) abnormality, there are relatively few studies on the prevalence of silent cerebral infarction (SCI) on magnetic resonance imaging (MRI) and vasculopathy on MR angiography (MRA), paricularly in Africa, where the burden of disease is greatest. In this study in Africa, we determined the prevalence of SCI on MRI and cerebral vasculopathy on MRA, and explored associations with age, sex, internal carotid/middle cerebral artery (ICA/MCA) and basilar cerebral blood flow velocities (CBFV) on TCD, and hematological variables.Patients and methods:We prospectively studied children with homozygous SCA (HbSS) without prior clinically overt stroke or TIA or seizures. Clinical information and blood for full blood count was collected for all patients. All were offered TCD using non-imaging equipment (Compumedics) and MRI and MRA of intracranial arteries on a Philips 1.5 Tesla scanner. MRA was graded as 1 Turbulence, 2 Stenosis, 3 Occlusion, 4 Occlusion with collaterals (moyamoya). Imaging was reviewed by 2 neuroradiologists (MJ and DS) and consensus was reached.Results:Within a period of 12 months, 395 children with SCA were recruited. Mean age was 12.7+/-4 (range 5-19 years); 199 (50.4%) were male. Mean hemoglobin was 7.6±1.1 (range 4.1-13.5) g/dl. 381 had TCD, of whom 227 (57%) have had brain MRI and MRA so far.Only 14/395 (3.5%) of patients had abnormal CBFV, 8 (2%) with maximum CBFV 200cm/sec).Prevalence of silent cerebral infarction was 29% (65/227) and was similar in males (30%; 34/114) and females (28%; 31/110) but was lower in children age
Postpartum pituitary hypophysitis
No full textThe case of a young woman who developed lymphocytic hypophysitis 2 weeks after delivery of a healthy baby is reported. The patient presented with clinical features suggestive of a pituitary mass lesion, but surgery was avoided when other clinical and radiologic features were considered. The patient recovered with steroid treatment only. We review the literature on this increasingly recognized condition and argue that medical management may be more suitable than previously thought
MRI detection of brain abnormality in sickle cell disease
No full textIntroduction: Over the past decades, neuroimaging studies have clarified that a significant proportion of patients with sickle cell disease (SCD) have functionally significant brain abnormalities. Clinically, structural magnetic resonance imaging (MRI) sequences (T2, FLAIR, diffusion-weighted imaging) have been used by radiologists to diagnose chronic and acute cerebral infarction (both overt and clinically silent), while magnetic resonance angiography and venography have been used to diagnose arteriopathy and venous thrombosis. In research settings, imaging scientists are increasingly applying quantitative techniques to shine further light on underlying mechanisms.Areas covered: From a June 2020 PubMed search of ‘magnetic’ or ‘MRI’ and ‘sickle’ over the previous 5 years, we selected manuscripts on T1-based morphometric analysis, diffusion tensor imaging, arterial spin labeling, T2-oximetry, quantitative susceptibility, and connectivity.Expert Opinion: Quantitative MRI techniques are identifying structural and hemodynamic biomarkers associated with risk of neurological and neurocognitive complications. A growing body of evidence suggests that these biomarkers are sensitive to change with treatments, such as blood transfusion and hydroxyurea, indicating that they may hold promise as endpoints in future randomized clinical trials of novel approaches including hemoglobin F upregulation, reduction of polymerization, and gene therapy. With further validation, such techniques may eventually also improve neurological and neurocognitive risk stratification in this vulnerable population
Impact of frontal white matter lesions on performance monitoring: ERP evidence for cortical disconnection
No full textWe examined the impact of discrete white matter lesions in the frontal lobes on event-related potential (ERP) correlates of performance monitoring. We tested the hypothesis that abnormal performance monitoring may result from injury to white matter without evidence of injury to grey matter in the frontal lobes. It was predicted that such lesions may result in disconnection of the lateral and medial frontal cortices. The close interaction of these two areas has been implicated in performance monitoring. Two fast-choice response tasks were administered to patients with MRI-confirmed frontal white matter lesions due to sickle cell disease (SCD) vasculopathy (n = 11; age = 11-23 years; 6 unilateral left lesions and 5 bilateral lesions) and two control groups: SCD patients without brain lesions and non-sickle cell sibling controls (n = 11 each). Stimulus-locked ERP components N2 and P3 were not significantly affected by presence of lesions. The difference between response-locked components to correct trials (correct-response negativity--CRN) and erroneous trials (error-related negativity--ERN) was diminished in patients with unilateral and bilateral frontal white matter lesions. This finding was due to a significantly attenuated ERN amplitude in lesion patients compared with both sibling and non-lesion control groups. These ERP findings were not due to performance differences between groups and hence reflect a compromised neural substrate underlying performance monitoring. The latter may also contribute to the deficits in executive function tasks observed in these patients. As disruption to ERP markers of error processing was found in the absence of lesions to the lateral or medial frontal cortex, we conclude that a functional connection between these areas facilitates performance monitoring, possibly implemented via tracts traversing the deep frontal white matter.<br/
Stroke in childhood neurofibromatosis type 2
Full text linkThis commentary is on the case series by Lascelles et al. on pages 1285–1288 of this issue
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
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