Biomedical subjects

Javier Mateos

Publications and source records attributed to Javier Mateos.

3 recordsLinked to original sources

PubMed2006

Blind deconvolution using a variational approach to parameter, image, and blur estimation.

Following the hierarchical Bayesian framework for blind deconvolution problems, in this paper, we propose the use of simultaneous autoregressions as prior distributions for both the image and blur, and gamma distributions for the unknown parameters (hyperparameters) of the priors and the image formation noise. We show how the gamma distributions on the unknown hyperparameters can be used to prevent the proposed blind deconvolution method from converging to undesirable image and blur estimates and also how these distributions can be inferred in realistic situations. We apply variational methods to approximate the posterior probability of the unknown image, blur, and hyperparameters and propose two different approximations of the posterior distribution. One of these approximations coincides with a classical blind deconvolution method. The proposed algorithms are tested experimentally and compared with existing blind deconvolution methods.

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PubMed2006

[Clinical value of the ankle-brachial index in patients at risk of cardiovascular disease but without known atherothrombotic disease: VITAMIN study].

INTRODUCTION AND OBJECTIVES: Detecting peripheral arterial disease by measuring the ankle-brachial index can help identify asymptomatic patients with established disease. We investigated the prevalence of peripheral arterial disease (i.e., an ankle-brachial index <0.9) and its potential clinical and therapeutic impact in patients with no known arterial disease who were seen at internal medicine departments. METHODS: This multicenter, cross-sectional, observational study included patients at risk of cardiovascular disease who were selected on the basis of age, gender and the presence of conventional risk factors. No patient was known to have arterial disease. RESULTS: The study included 493 patients, 174 (35%) of whom had diabetes, while 321 (65%) did not. Only 16% were in a low-risk category according to their Framingham score. An ankle-brachial index <0.9 was observed in 27.4%, comprising 37.9% of those with diabetes and 21.3% of those without. Multiple logistic regression analysis showed that the risk factors associated with an ankle-brachial index <0.9 were age, diabetes, and hypercholesterolemia. There was a significant relationship between the ankle-brachial index and Framingham risk categories. Therapeutically, only 21% of patients with an ankle brachial index <0.9 were taking antiplatelet drugs. Overall, 20% had a low-density lipoprotein cholesterol concentration <100 mg/dl and 52% had a concentration <130 mg/dl. Some 42% had arterial blood pressures below 140/90 mm Hg. CONCLUSIONS: Asymptomatic peripheral arterial disease was detected in a high proportion of patients with an intermediate or high cardiovascular disease risk. The ankle-brachial index should be measured routinely in patients at risk of cardiovascular disease who are seen at internal medicine departments.

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PubMed2004

Bayesian resolution enhancement of compressed video.

Super-resolution algorithms recover high-frequency information from a sequence of low-resolution observations. In this paper, we consider the impact of video compression on the super-resolution task. Hybrid motion-compensation and transform coding schemes are the focus, as these methods provide observations of the underlying displacement values as well as a variable noise process. We utilize the Bayesian framework to incorporate this information and fuse the super-resolution and post-processing problems. A tractable solution is defined, and relationships between algorithm parameters and information in the compressed bitstream are established. The association between resolution recovery and compression ratio is also explored. Simulations illustrate the performance of the procedure with both synthetic and nonsynthetic sequences.

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