1,721,028 research outputs found
Improving the image quality of contrast-enhanced MR angiography by automated image registration: A prospective study in peripheral arterial disease of the lower extremities
No full textObjective: If a patient has moved during digital subtraction angiography (DSA), manual pixel shift can improve the image quality. This study investigated whether such image registration can also improve the quality of contrast-enhanced magnetic resonance angiography (MRA) in patients with peripheral arterial disease of the lower extremities. Materials and methods: 404 leg MRAs of patients likely to have peripheral artery disease were included in this prospective study. The standard non-registered MRAs were compared to automatically linear, affine and warp registered MRAs by four image quality parameters, including the vessel detection probability (VDP) in maximum intensity projection (MIP) images and contrast-to-noise ratios (CNR). The different registration types were compared by analysis of variance. Results: All studied image quality parameters showed similar trends. Generally, registration improved the leg MRA quality significantly (P < 0.05). The 12% of lower legs with a body shift of 1 mm or more showed the highest gain in image quality when using linear registration instead of no registration, with an average VDP gain of 20-49%. Warp registration improved the image quality slightly further. Conclusion: Automated image registration can improve the MRA image quality especially in the lower legs, which is comparable to the effect of pixel shift in DSA. (C) 2009 Elsevier Ireland Ltd. All rights reserved
Comparison of different body size parameters for individual dose adaptation in body CT of adults
No full textPURPOSE: To investigate prospectively which of several body size parameters are suitable for individual dose adaptation in body computed tomography (CT) of adults. MATERIALS AND METHODS: Three body regions (thorax, abdomen, pelvis) were scanned exclusively for clinical reasons, with institutional ethical approval and informed consent. For each of the three regions, 50 men and 50 women (aged 18-87 years) were studied (300 scans total). Individual x-ray properties for each scan were summarized with a water-equivalent diameter (D-w). Different body size parameters, based on weight, height, and shape, were correlated with D-w by using regression analysis. This resulted in D-w estimation errors of different magnitudes, indicated with 95% prediction intervals. The errors from weight were compared with those from each of the other body parameters by using comparison of variance in paired samples (P < .05). In addition, a topogram-based estimate for D-w was studied, which simulated an automated body size measurement. RESULTS: For the thorax, abdomen, and pelvis, mean D-w was 28.0, 29.1, and 29.3 cm, and estimation of D-w from weight enabled 95% prediction intervals of +/- 2.5, +/- 2.4, and +/- 2.6 cm, respectively. Combinations of height and weight were only slightly more or even less exact than were measurements from only weight. Diameter-related parameters such as body circumference were similar to or better than weight. However, the topogram-based estimate was significantly more exact. CONCLUSION: Body weight and circumference enable suitable estimates for individual dose adaptation in body CT of adults if automated dose adaptation is not available. (c) RSNA, 2005
Bivariate Random-effects Meta-analysis of Sensitivity and Specificity with SAS PROC GLIMMIX
No full textObjectives: Meta-analysis allows to summarize pooled sensitivities and specificities from several primary diagnostic test accuracy studies. Often these pooled estimates are indirectly obtained from a hierarchical summary receiver operating characteristics (HSROC) analysis. This article presents a generalized linear random-effects model with the new SAS PROC GLIMMIX that obtains the pooled estimates for sensitivity and specificity directly. Methods: Firstly, the formula of the bivariate random-effects model is presented in context with the literature. Then its implementation with the new SAS PROC GLIMMIX is empirically evaluated in comparison to the indirect HSROC approach, utilizing the published 2 x 2 count data of 50 meta-analyses. Results: According to the empirical evaluation the meta-analytic results from the bivariate GLIMMIX approach are nearly identical to the results from the indirect HSROC approach. Conclusions: A generalized linear mixed model with PROC GLIMMIX offers a straightforward method for bivariate random-effects meta-analysis of sensitivity and specificity
Diagnostic Accuracy of Multidetector CT in Acute Mesenteric Ischemia: Systematic Review and Meta-Analysis
No full textPurpose: To use meta-analysis to determine the diagnostic accuracy of contrast agent–enhanced multidetector computed tomography (CT) in primary acute mesenteric ischemia (AMI). Materials and Methods: The PubMed search engine and fi ve other electronic databases were searched for “mesenteric ischemia,” “computed tomography,” and related terms in articles published between January 1996 and September 2009, without language restrictions. Reference lists of retrieved articles were also searched. Two reviewers independently selected six studies that reported 2 3 2 contingency data on the diagnostic accuracy of multidetector CT in primary AMI in at least 10 patients with disease and 10 patients without disease and that used surgery or clinical outcome as the reference standard. Study data were independently extracted by the two reviewers, and disagreement was resolved by consensus. The study quality was assessed by using items from the Quality Assessment of Diagnostic Accuracy Studies tool. The primary 2 3 2 count data were investigated with a bivariate random-effects meta-analysis of sensitivity and specifi city. Results: Three studies were prospective, and three were retrospective. All studies were of high quality. The CT scanners used in the included studies had between four and 40 rows. The between-study heterogeneity was low to moderate. Overall, AMI was found in 142 of 619 studied cases. The meta-analysis showed a pooled sensitivity of 93.3% (95% confi dence interval: 82.8%, 97.6%) and a pooled specifi city of 95.9% (95% confi dence interval: 91.2%, 98.2%). Conclusion: On the basis of a thorough clinical examination, contrastenhanced multidetector CT allows the diagnosis of primary AMI with high sensitivity and specifi city. Thus, it may be used as the fi rst-line imaging method
Bivariate Random-Effects Meta-analysis of Sensitivity and Specificity with the Bayesian SAS PROC MCMC: Methodology and Empirical Evaluation in 50 Meta-analyses
No full textBackground and Objective: Meta-analysis allows for summarizing the sensitivities and specificities from several primary diagnostic test accuracy studies quantitatively. This article presents and evaluates a full Bayesian method for bivariate random-effects meta-analysis of sensitivity and specificity with SAS PROC MCMC. Methods: First, the formula of the bivariate random-effects model is presented. Then its implementation with the Bayesian SAS PROC MCMC is empirically evaluated, using the published 2 x 2 count data of 50 meta-analyses. The convergence of the Markov chains is analyzed visually and qualitatively. The results are compared with a Bayesian WinBUGS approach, using the Bland-Altman analysis for assessing agreement between 2 methods. Results: The 50 meta-analyses covered broad ranges of pooled sensitivity (17.4% to 98.8%) and specificity (60.0% to 99.7%), and the between-study heterogeneity varied as well. In all meta-analyses, the Markov chains converged well. The meta-analytic results from the SAS PROC MCMC and the WinBUGS random-effects approaches were nearly similar, showing close 95% limits of agreement for the pooled sensitivity (-0.06% to 0.05%) and specificity (-0.05% to 0.05%) without significant differences (P > 0.05). This indicates that the bivariate model is well implemented with both different statistical programs, without systematic differences arising from program attributes. Conclusions: As alternative to a WinBUGS approach, the Bayesian SAS PROC MCMC is well suited for bivariate random-effects meta-analysis of sensitivity and specificity
Diagnostic Accuracy of Multidetector CT in Acute Mesenteric Ischemia: Systematic Review and Meta-Analysis
No full textPurpose: To use meta-analysis to determine the diagnostic accuracy of contrast agent–enhanced multidetector computed tomography (CT) in primary acute mesenteric ischemia (AMI). Materials and Methods: The PubMed search engine and fi ve other electronic databases were searched for “mesenteric ischemia,” “computed tomography,” and related terms in articles published between January 1996 and September 2009, without language restrictions. Reference lists of retrieved articles were also searched. Two reviewers independently selected six studies that reported 2 3 2 contingency data on the diagnostic accuracy of multidetector CT in primary AMI in at least 10 patients with disease and 10 patients without disease and that used surgery or clinical outcome as the reference standard. Study data were independently extracted by the two reviewers, and disagreement was resolved by consensus. The study quality was assessed by using items from the Quality Assessment of Diagnostic Accuracy Studies tool. The primary 2 3 2 count data were investigated with a bivariate random-effects meta-analysis of sensitivity and specifi city. Results: Three studies were prospective, and three were retrospective. All studies were of high quality. The CT scanners used in the included studies had between four and 40 rows. The between-study heterogeneity was low to moderate. Overall, AMI was found in 142 of 619 studied cases. The meta-analysis showed a pooled sensitivity of 93.3% (95% confi dence interval: 82.8%, 97.6%) and a pooled specifi city of 95.9% (95% confi dence interval: 91.2%, 98.2%). Conclusion: On the basis of a thorough clinical examination, contrastenhanced multidetector CT allows the diagnosis of primary AMI with high sensitivity and specifi city. Thus, it may be used as the fi rst-line imaging method
Bayesian bivariate meta-analysis of sensitivity and specificity: summary of quantitative findings in 50 meta-analyses
No full textRationale, aims and objectives Meta-analyses of diagnostic test accuracy are important elements in evidence-based medicine. However, currently there is no overview of related quantitative findings that were obtained in a large number of real meta-analyses. This study aimed at providing such empirical summary. Methods From the literature 50 meta-analyses were randomly selected that had reported their 2 x 2 count data of sensitivity and specificity. Descriptive statistics, assessment of between-study heterogeneity and bivariate random-effects meta-analysis of sensitivity and specificity were performed with a novel Bayesian program code. The bivariate model parameters were also converted to the parameters of the closely related hierarchical summary receiver operating characteristic (HSROC) model. Results Among the 50 meta-analyses, the studies per meta-analysis ranged from 5 to 45 and the disease prevalence from 2.3 to 71%. Significant between-study heterogeneity was found in 43 of 50 meta-analyses, favouring a random-effects model over a fixed-effects model. Empirical distributions of sensitivity and specificity, positive and negative likelihood ratios, and other model results are presented in the full text numerically and graphically. Conclusions Studies of diagnostic test accuracy can be well meta-analysed within a Bayesian framework, and the presented quantitative findings provide an orientation when interpreting the results of the standard bivariate/HSROC model
Photoacoustic breast tomography prototypes with reported human applications
No full textPhotoacoustic breast tomography could provide optical molecular imaging with near-infrared light at sonographic image resolution by utilizing the photoacoustic effect. This review summarizes reports about current prototypes that were applied in vivo in humans. Four databases were searched for reports about prototypes of photoacoustic breast tomography that were tested in vivo in humans. Data extracted from the reports comprised details about system design, phantom studies, and clinical studies. Five prototypes were included. System designs comprised planar, hemicylindrical and hemispherical geometries. In total, 52 of 61 breast cancers (85 %) were detected by three of the prototypes, showing image details such as ring-pattern of the haemoglobin-rich tumour vasculature. A refined prototype provided submillimetre resolution at a good contrast-to-noise ratio up to a depth of about 5 cm in a cup-shaped breast configuration. Another novel prototype demonstrated that in the mammographic imaging geometry, the total imaging depth approximately duplicates with bilateral laser illumination. Most prototypes focused on detecting elevated haemoglobin content related to tumours, but proof-of-principle was also given for multispectral optoacoustic tomography by additional imaging of tissue oxygenation. Photoacoustic breast tomography can detect breast cancer. This radiation-free molecular imaging technology should be further refined and studied for clinical applications
Contrast-enhanced magnetic resonance angiography in peripheral arterial disease: Improving image quality by automated image registration
No full textIn peripheral arterial disease, contrast-enhanced MR angiography (MRA) is a noninvasive imaging alternative for catheter-based digital subtraction angiography (DSA). In DSA, final images are generated by subtracting a native mask image from subsequent contrast-enhanced images. Image quality is routinely improved by digitally shifting the mask image prior to subtraction if the patient has moved during angiography. This study investigated whether such image registration may also help to improve the image quality of MRA. In all, 545 MRA examinations of pelvic and leg arteries in patients with symptoms of peripheral arterial disease were studied retrospectively. Standard nonregistered MRA was compared to automatically linear, affine, and warp registered MRA by visual analysis and by three image quality parameters, including vessel detection probability (VDP) of angiographic maximum intensity projections. Most MRA of pelvic and upper leg arteries showed good nonregistered image quality. However, the 15% of lower legs with a body shift of 1 mm or more had relatively low nonregistered image quality, which improved significantly with image registration (VDP gain more than 18%, P < 0.05). The visual analysis gave similar results. In conclusion, image registration can improve image quality of MRA in peripheral arterial disease, especially in the lower legs
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