1,720,961 research outputs found
Imaging in dementia with Lewy bodies: a review
No full textThis review discusses the role of functional and structural imaging in patients with suspected dementia with Lewy bodies, with particular emphasis on SPECT and PET dopaminergic and cerebral perfusion/metabolic techniques. It is envisaged that this information may be useful to nuclear medicine physicians, radiologists, psychiatrists, neurologists, geriatricians and physician
Simulation of realistic abnormal SPECT brain perfusion images: application in semi-quantitative analysis
No full textSimulation is useful in the validation of functional image analysis methods, particularly when considering the number of analysis techniques currently available lacking thorough validation. Problems exist with current simulation methods due to long run times or unrealistic results making it problematic to generate complete datasets. A method is presented for simulating known abnormalities within normal brain SPECT images using a measured point spread function (PSF), and incorporating a stereotactic atlas of the brain for anatomical positioning. This allows for the simulation of realistic images through the use of prior information regarding disease progression. SPECT images of cerebral perfusion have been generated consisting of a control database and a group of simulated abnormal subjects that are to be used in a UK audit of analysis methods. The abnormality is defined in the stereotactic space, then transformed to the individual subject space, convolved with a measured PSF and removed from the normal subject image. The dataset was analysed using SPM99 (Wellcome Department of Imaging Neuroscience, University College, London) and the MarsBaR volume of interest (VOI) analysis toolbox. The results were evaluated by comparison with the known ground truth. The analysis showed improvement when using a smoothing kernel equal to system resolution over the slightly larger kernel used routinely. Significant correlation was found between effective volume of a simulated abnormality and the detected size using SPM99. Improvements in VOI analysis sensitivity were found when using the region median over the region mean. The method and dataset provide an efficient methodology for use in the comparison and cross validation of semi-quantitative analysis methods in brain SPECT, and allow the optimization of analysis parameters
Measurement of cerebral perfusion volume and 99mTc-HMPAO uptake using SPECT in controls and patients with Alzheimer's disease
No full textMethods for quantifying the changes in brain function observed in single photon emission computed tomography (SPECT) using hexamethylenepropylene amine oxime (HMPAO) for patients with Alzheimer's disease have the potential of improving the diagnostic accuracy of the procedure and its ability to monitor response to treatment. The absolute percentage uptake of HMPAO and the cerebral perfusion volume (CPV) of the brain were assessed using SPECT in 26 patients with mild to moderate Alzheimer's disease (AD) and 24 control subjects. A subset of 15 control subjects, which was age-matched to the AD patients, was selected to allow fair statistical comparison of parameters between groups. The percentage of brain volume with reduced perfusion (R) and a volume loss index (VLI), given by R1/2/CPV, were also calculated. Eight of the control subjects were studied on a second occasion after a mean period of 6 months. There was no significant difference in percentage uptake between controls and AD patients, the mean value being 5.8%. Cerebral perfusion volume in controls was found to depend on sex (mean value in males and females being 1327 ml and 1222 ml, respectively) and on age. The volume loss index corrected for age and sex provided good discrimination between controls and AD subjects giving a sensitivity and specificity of 81% and 96%, respectively. The repeatability coefficient, the 95% confidence limit for the difference between repeat measurements, on controls was 67 ml (5%). The measurement of cerebral perfusion volume and related indices may be of value in identifying patients with early Alzheimer's disease and in following their response to treatment
Limitations of the HMPAO SPECT appearances of occipital lobe perfusion in the differential diagnosis of dementia with Lewy bodies
No full textObjective To assess the utility of the appearances of occipital lobe perfusion on HMPAO SPECT in the diagnosis of dementia with Lewy bodies (DLB) using the I-123-FP-CIT findings as the diagnostic 'gold standard'. Methods Eighty-four consecutive patients underwent both HMPAO SPECT and I-123-FP-CIT as part of their routine investigations for suspected DLB. Results Thirty-nine of the 84 FP-CIT scans were abnormal indicating a prevalence of 44% of patients with DLB in this series. In those patients classified as DLB, 28% of HMPAO SPECT scans demonstrated occipital hypoperfusion. In those patients with a dementia other than DLB 31% of patients demonstrated occipital hypoperfusion (P=0.8). Conclusion Occipital lobe hypoperfusion as demonstrated by HMPAO SPECT in patients with suspected Lewy body dementia does not appear to be able to either rule in, or rule out, the diagnosis of DL
Alzheimer's disease: differences in technetium-99m HMPAO SPECT scan findings between early onset and late onset dementia
No full textObjective: to compare the HMPAO SPECT cerebral perfusion patterns in early and late onset Alzheimer’s disease.Methods: twenty patients with early onset disease (<65 years) and 44 patients with late onset disease (>65 years) were studied. All patients fulfilled NINCDS-ADRDA clinical criteria and had details of disease severity and length of history at the time of imaging. Technetium-99m HMPAO SPECT brain scans were acquired on a multi-detector gammacamera and analysed visually and with statistical parametric mapping (SPM99).Results: patients with early onset disease had significantly greater posterior cortical association area involvement whereas those with late onset disease had significantly greater medial temporal hypoperfusion. These findings were unchanged after controlling for disease severity and length of illness.Discussion: these functional imaging findings of the differences between early and late onset Alzheimer’s disease are supported by published findings that include histopathological and clinical evidence; namely late onset patients tend to present with the characteristic involvement of the medial temporal lobes producing marked memory loss whereas early onset patients present with predominant posterior cortical association area involvement. These age related findings should be borne in mind when clinically diagnosing, and interpreting functional brain imaging studies in, patients with suspected Alzheimer’s disease
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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