1,720,958 research outputs found
New and Evolving Concepts in the Imaging and Management of Urolithiasis: Urologists' Perspective
No full textUrolithiasis is a universal problem that has become increasingly prevalent in the United States and has a high rate of recurrence. Imaging of urolithiasis has evolved over the years due to technologic advances and a better understanding of the disease process. Computed tomography (CT) has been the investigation of choice for the evaluation of urinary stone disease. The emergence of multidetector CT and the recent introduction of dual-energy CT have further reinforced the superiority of this modality over other imaging techniques in the management of urolithiasis. Multidetector CT is not limited to simply helping make an accurate diagnosis in patients with stone disease; it is also useful in the assessment of stone burden, composition, and fragility, findings that are helpful in determining appropriate treatment strategies. In addition, multidetector CT is a valuable tool in the follow-up of patients after urologic intervention or institution of medical therapy. Familiarity with recent technologic developments will help radiologists meet the growing expectations of urologists in this setting. In addition, radiologists should be aware of the radiation risks inherent in the imaging of patients with urolithiasis and take appropriate measures to minimize this risk and optimize image quality. (C) RSNA, 2010 .radiographics.rsna.or
Differences in Computed Tomography Density of the Renal Papillae of Stone Formers and Non-Stone-Formers: A Pilot Study
No full textPurpose: It is thought that Randall's plaques, calcium deposits in the renal papillae of patients with nephrolithiasis, may serve as a nidus for stone formation. We examined the density of renal papillae in patients with stones and control patients using attenuation measurements (HU) on Computed Tomography (CT) to determine whether nephrolithiasis is associated with radiographic changes in renal papillae. Materials and Methods: Hounsfield density measurements of a 0.2cm(2) area of the renal papillae of 17 patients with a single renal calyceal calculus and 15 age- matched control patients were performed. Measurements were done for renal papillae upper, middle, and lower pole calyces for all patients. Statistical comparisons were made using the student's t-test. Results: Patients with nephrolithiasis and control patients were similar with respect to mean age (41.2 years versus 42.2 years, p = 0.82) and baseline serum creatinine (0.86 mg/dl versus 0.93 mg/dl, p = 0.21). Mean Hounsfield density of renal papillae of stone patients in calyces with stones was significantly greater than that of location- matched papillae from control patients (54.4 versus 36.6, p < 0.0001). Mean Hounsfield density of all papillae of the affected kidney (i. e., kidney with stone) in stone patients was significantly greater than that of control patients (50.9 versus 36.4, p < 0.0001). Mean Hounsfield density of all papillae in the stone- free kidney of stone patients was significantly greater than that of control patients (50.0 versus 36.1, p < 0.0001). In stone patients, when comparing the affected kidney with the stone- free kidney, there was no difference in mean papilla Hounsfield density (50.3 versus 50.9, p = 0.59). Conclusions: Hounsfield density of the renal papilla is significantly increased in patients with nephrolithiasis when compared with age- matched controls. This is true of calyces with stones, calyces without stones in kidneys with stones, and calyces of the contralateral stone- free kidney. There is no difference in renal papilla Hounsfield density between kidneys with and without stones in patients with nephrolithiasis. In the future, this information may be useful in predicting which patients may develop nephrolithiasis
History of kidney stones and the risk of coronary heart disease
No full textKidney stone disease is common and may be associated with an increased risk of coronary heart disease (CHD). Previous studies of the association between kidney stones and CHD have often not controlled for important risk factors, and the results have been inconsistent
Differential Renal Function Estimation Using Computerized Tomography Based Renal Parenchymal Volume Measurement
No full textPurpose: Nuclear renal scan is currently the gold standard imaging study to determine differential renal function. We propose helical computerized tomography as a more efficient way to gain renal function information. Renal parenchymal volume is measured and percent total renal volume is used as a surrogate marker for differential renal function. Materials and Methods: Computerized tomography and diuretic enhanced nuclear renal scan were performed in 33 patients with chronic obstruction. Computerized tomography was contrast enhanced in 23 cases and nonenhanced in 10. Diagnoses included ureteropelvic junction obstruction, ureteral stricture and extrinsic compression. Using semiautomated boundary delineation with manual editing method the parenchymal volume of each kidney was measured and percent renal volume was calculated. Percent renal volume was compared with percent renal function, as determined by nuclear renal scan. Correlations between the 2 measures were evaluated using the Spearman or Pearson coefficient. Results: Strong correlations were observed between percent renal function and percent renal volume in all cases (r = 0.90, p < 0.001), including the enhanced (r = 0.87, p < 0.001) and nonenhanced (r = 0.95, p < 0.001) groups. Moderately strong correlations were noted in the less than 40% (r = 0.76, p < 0.001) and less than 30% (r = 0.64, p = 0.015) renal function subgroups. Conclusions: Differential renal volume measured from computerized tomography strongly correlates with differential renal function on nuclear renal scan for normal and chronically obstructed kidneys. Computerized tomography may serve as a single radiological diagnostic study for anatomical and functional assessment in patients in whom a poorly functioning kidney is suspected
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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