The Experts below are selected from a list of 317787 Experts worldwide ranked by ideXlab platform
Lyly Teppo - One of the best experts on this subject based on the ideXlab platform.
-
health effects of cadmium exposure a review of the literature and a Risk Estimate
Scandinavian Journal of Work Environment & Health, 1998Co-Authors: Lyly TeppoAbstract:Environmental exposures occupy an important position in cancer causation. Even if the etiologic fractions associated with various life-style factors such as smoking, diet, alcohol consumption, and sexual habits may, according to current knowledge, be greater than those of exposures occurring in the human environment, it is often easier to change the environment than to make individuals change their life-style and habits into healthier modes. Through legislation and various technical measures it is often possible to regulate the occurrence of different carcinogenic agents in the human environment and to diminish exposures to them as has been done with, for example, carcinogens at workplaces, ionizing radiation, and ambient air and water pollution. Before regulatory measures can be undertaken, the individual exposures and their relative importance should be known. Useful information is obtained through laboratory research, but its relevance in the human setting should, when possible, be confirmed on the population level, that is, by using epidemiologic methods. Such questions as how high are the relative Risks associated with exposures that occur in real life, how long are the latencies, and are there important interactions need to be answered. In countries and areas where a well-functioning cancer registry exists, epidemiologic cancer research is greatly facilitated. If a cohort defined by exposure to a suspected agent can be created, cases of cancer can be identified for the registry files by applying usual cohort study methodology. Cancer registry may also be able to produce unbiased case series for case-referent studies, and these data are especially important when rare cancers are concerned. (The number of cases would be too small in any cohort study.) Quite often, a case-referent approach within a cohort is used. In each Nordic country there is a cancer registry covering the entire population of the country, and the individual person numbers available in the countries make the record linkage between study cohorts and registry files a technically easy procedure, and it has been successfully used in a large number of epidemiologic studies on both the national and Nordic level. Confidentiality rules concerning the registries are reasonable and have not caused undue problems for appropriate epidemiologic studies. The Nordic cancer registries have participated in several studies in which environmental exposures have been analyzed in terms of cancer Risks. In Finland, both cohort studies and case-referent studies have been conducted, recently focusing, for example, on low-intensity magnetic fields produced by high-voltage powerlines (only a marginal increase in the Risk of adult leukemia found), chlorophenols in drinking water after leakage from a sawmill (Risk of non-Hodgkin's lymphoma slightly increased), and ionizing radiation caused by radon daughters from the earth (suggestive increase in the Risk of lung cancer) or by fallout from the Chernobyl accident (no increase in the Risk of childhood leukemia). Further studies in which data from cancer registries have been successfully utilized include an evaluation of the cancer Risks associated with several exposures in the work environment, the Risk of leukemia among people who live close to an oil refinery, the Risk of cancer associated with the mutagenicity of drinking water due to chlorination procedures, and the Risk of sarcoma and other cancers among herbicide users. In this issue of the Scandinavian Journal of Work, Environment & Health , a review article is published on environmental Risk factors in breast cancer by Esther A Welp and her co-workers. In their conclusions, the authors end with several proposals for future studies. These proposals are well focused. Breast cancer is one of the most common cancers in the western world. In spite of extensive research carried out for decades in all parts of the world, simple effective preventive measures are still lacking. The strongest Risk factors that have been found are related to endogenous estrogen load and the reproductive history of women, but these factors can only explain a part of all breast cancers. Moreover, even if many of these factors are well characterized, it is difficult, if not impossible, to utilize them in prevention. Thus better understanding of the environmental Risk factors for breast cancer would be extremely important. Although the relative Risks associated with them are probably low, a large number of women are likely to be exposed, the result being substantial numbers of preventable cancers. One group of chemicals in the human environment that is of interest in terms of breast cancer causation is the group of so-called hormone disruptors. They are compounds with weak estrogenic effects in animal experiments or in vitro studies. Examples of these chemicals are organochlorine compounds (DDT, PCB, etc), phthalates, tributyltin compounds, and alkylphenols. They occur in pesticides, paints and plastic products, anti-fouling agents, and many other products used in a variety of ways. Many people are exposed to them in their workplaces and everyday life -- often without knowing it. An association between hormone disruptors and male infertility, cryptorchidism, and testis cancer has been suggested, and epidemiologic studies on these issues have been made. In addition the hypothesis of a link between exposure to hormone disruptors and breast cancer is biologically plausible. Data supporting this association are increasing, but problems will arise even in well-designed epidemiologic studies. Reliable data on life-long exposures to hormone disruptors are difficult to obtain, and studies based on chemical analyses of fat tissue from cases and referents (aiming at estimation of exposures) have their limitation. Still almost everyone in western populations is exposed to them at least to some extent. Collaboration between different areas is needed in modern cancer epidemiologic research. Solving the problem of the association between hormone disruptors and breast cancer causation calls for cooperation between epidemiologists, chemists, endocrinologists, cell biologists, and experts in gene research. And behind all these are the cancer registers with their data on cancer patients, which may be helpful in certain approaches.
-
health effects of cadmium exposure a review of the literature and a Risk Estimate
Scandinavian Journal of Work Environment & Health, 1998Co-Authors: Lyly TeppoAbstract:Environmental exposures occupy an important position in cancer causation. Even if the etiologic fractions associated with various life-style factors such as smoking, diet, alcohol consumption, and sexual habits may, according to current knowledge, be greater than those of exposures occurring in the human environment, it is often easier to change the environment than to make individuals change their life-style and habits into healthier modes. Through legislation and various technical measures it is often possible to regulate the occurrence of different carcinogenic agents in the human environment and to diminish exposures to them as has been done with, for example, carcinogens at workplaces, ionizing radiation, and ambient air and water pollution. Before regulatory measures can be undertaken, the individual exposures and their relative importance should be known. Useful information is obtained through laboratory research, but its relevance in the human setting should, when possible, be confirmed on the population level, that is, by using epidemiologic methods. Such questions as how high are the relative Risks associated with exposures that occur in real life, how long are the latencies, and are there important interactions need to be answered. In countries and areas where a well-functioning cancer registry exists, epidemiologic cancer research is greatly facilitated. If a cohort defined by exposure to a suspected agent can be created, cases of cancer can be identified for the registry files by applying usual cohort study methodology. Cancer registry may also be able to produce unbiased case series for case-referent studies, and these data are especially important when rare cancers are concerned. (The number of cases would be too small in any cohort study.) Quite often, a case-referent approach within a cohort is used. In each Nordic country there is a cancer registry covering the entire population of the country, and the individual person numbers available in the countries make the record linkage between study cohorts and registry files a technically easy procedure, and it has been successfully used in a large number of epidemiologic studies on both the national and Nordic level. Confidentiality rules concerning the registries are reasonable and have not caused undue problems for appropriate epidemiologic studies. The Nordic cancer registries have participated in several studies in which environmental exposures have been analyzed in terms of cancer Risks. In Finland, both cohort studies and case-referent studies have been conducted, recently focusing, for example, on low-intensity magnetic fields produced by high-voltage powerlines (only a marginal increase in the Risk of adult leukemia found), chlorophenols in drinking water after leakage from a sawmill (Risk of non-Hodgkin's lymphoma slightly increased), and ionizing radiation caused by radon daughters from the earth (suggestive increase in the Risk of lung cancer) or by fallout from the Chernobyl accident (no increase in the Risk of childhood leukemia). Further studies in which data from cancer registries have been successfully utilized include an evaluation of the cancer Risks associated with several exposures in the work environment, the Risk of leukemia among people who live close to an oil refinery, the Risk of cancer associated with the mutagenicity of drinking water due to chlorination procedures, and the Risk of sarcoma and other cancers among herbicide users. In this issue of the Scandinavian Journal of Work, Environment & Health , a review article is published on environmental Risk factors in breast cancer by Esther A Welp and her co-workers. In their conclusions, the authors end with several proposals for future studies. These proposals are well focused. Breast cancer is one of the most common cancers in the western world. In spite of extensive research carried out for decades in all parts of the world, simple effective preventive measures are still lacking. The strongest Risk factors that have been found are related to endogenous estrogen load and the reproductive history of women, but these factors can only explain a part of all breast cancers. Moreover, even if many of these factors are well characterized, it is difficult, if not impossible, to utilize them in prevention. Thus better understanding of the environmental Risk factors for breast cancer would be extremely important. Although the relative Risks associated with them are probably low, a large number of women are likely to be exposed, the result being substantial numbers of preventable cancers. One group of chemicals in the human environment that is of interest in terms of breast cancer causation is the group of so-called hormone disruptors. They are compounds with weak estrogenic effects in animal experiments or in vitro studies. Examples of these chemicals are organochlorine compounds (DDT, PCB, etc), phthalates, tributyltin compounds, and alkylphenols. They occur in pesticides, paints and plastic products, anti-fouling agents, and many other products used in a variety of ways. Many people are exposed to them in their workplaces and everyday life -- often without knowing it. An association between hormone disruptors and male infertility, cryptorchidism, and testis cancer has been suggested, and epidemiologic studies on these issues have been made. In addition the hypothesis of a link between exposure to hormone disruptors and breast cancer is biologically plausible. Data supporting this association are increasing, but problems will arise even in well-designed epidemiologic studies. Reliable data on life-long exposures to hormone disruptors are difficult to obtain, and studies based on chemical analyses of fat tissue from cases and referents (aiming at estimation of exposures) have their limitation. Still almost everyone in western populations is exposed to them at least to some extent. Collaboration between different areas is needed in modern cancer epidemiologic research. Solving the problem of the association between hormone disruptors and breast cancer causation calls for cooperation between epidemiologists, chemists, endocrinologists, cell biologists, and experts in gene research. And behind all these are the cancer registers with their data on cancer patients, which may be helpful in certain approaches.
-
health effects of cadmium exposure a review of the literature and a Risk Estimate
Scandinavian Journal of Work Environment & Health, 1998Co-Authors: Lyly TeppoAbstract:This report provides a review of the cadmium exposure situation in Sweden and updates the information on health Risk assessment according to recent studies on the health effects of cadmium. The report focuses on the health effects of low cadmium doses and the identification of high-Risk groups. The diet is the main source of cadmium exposure in the Swedish nonsmoking general population. The average daily dietary intake is about 15 micrograms/day, but there are great individual variations due to differences in energy intake and dietary habits. It has been shown that a high fiber diet and a diet rich in shellfish increase the dietary cadmium intake substantially. Cadmium concentrations in agricultural soil and wheat have increased continuously during the last century. At present, soil cadmium concentrations increase by about 0.2% per year. Cadmium accumulates in the kidneys. Human kidney concentrations of cadmium have increased several fold during the last century. Cadmium in pig kidney has been shown to have increased by about 2% per year from 1984-1992. There is no tendency towards decreasing cadmium exposure among the general nonsmoking population. The absorption of cadmium in the lungs is 10-50%, while the absorption in the gastrointestinal tract is only a few percent. Smokers have about 4-5 times higher blood cadmium concentrations (about 1.5 micrograms/l), and twice as high kidney cortex cadmium concentrations (about 20-30 micrograms/g wet weight) as nonsmokers. Similarly, the blood cadmium concentrations are substantially elevated in persons with low body iron stores, indicating increased gastrointestinal absorption. About 10-40% of Swedish women of child-bearing age are reported to have empty iron stores (S-ferritin < 12 micrograms/l). In general, women have higher concentrations of cadmium in blood, urine, and kidney than men. The population groups at highest Risk are probably smokers, women with low body iron stores, and people habitually eating a diet rich in cadmium. According to current knowledge, renal tubular damage is probably the critical health effect of cadmium exposure, both in the general population and in occupationally exposed workers. Tubular damage may develop at much lower levels than previously Estimated, as shown in this report. Data from several recent reports from different countries indicate that an average urinary cadmium excretion of 2.5 micrograms/g creatinine is related to an excess prevalence of renal tubular damage of 4%. An average urinary excretion of 2.5 micrograms/g creatinine corresponds to an average concentration of cadmium in renal cortex of 50 micrograms/g, which would be the result of long-term (decades) intake of 50 micrograms per day. When the critical concentrations for adverse effects due to cadmium accumulation are being evaluated, it is crucial to consider both the individual variation in kidney cadmium concentrations and the variations in sensitivity within the general population. Even if the population average kidney concentration is relatively low for the general population, a certain proportion will have values exceeding the concentration where renal tubular damage can occur. It can be Estimated that, at the present average daily intake of cadmium in Sweden, about 1% of women with low body iron stores and smokers may experience adverse renal effects related to cadmium. If the average daily intake of cadmium would increase to 30 micrograms/day, about 1% of the entire population would have cadmium-induced tubular damage. In Risk groups, for example, women with low iron stores, the percentage would be higher, up to 5%. Both human and animal studies indicate that skeletal damage (osteoporosis) may be a critical effect of cadmium exposure. We conclude, however, that the present evidence is not sufficient to permit such a conclusion for humans. We would like to stress, however, that osteoporosis is a very important public health problem worldwide, but especially in the Scandinav
Florian Luisier - One of the best experts on this subject based on the ideXlab platform.
-
A CURE for Noisy Magnetic Resonance Images: Chi-Square Unbiased Risk Estimation
2016Co-Authors: Florian Luisier, Thierry Blu, Patrick J. Wolfe, Senior MemberAbstract:Abstract — In this paper, we derive an unbiased expression for the expected mean-squared error associated with continuously differentiable estimators of the noncentrality parameter of a chi-square random variable. We then consider the task of denoising squared-magnitude magnetic resonance (MR) image data, which are well modeled as independent noncentral chi-square random variables on two degrees of freedom. We consider two broad classes of linearly parameterized shrinkage estimators that can be optimized using our Risk Estimate, one in the general context of undecimated filterbank transforms, and the other in the specific case of the unnormalized Haar wavelet transform. The resultant algorithms are computationally tractable and improve upon most state-of-the-art methods for both simulated and actual MR image data. Index Terms — Chi-square distribution, filterbank transform, image denoising, magnetic resonance (MR) imaging, Rician noise
-
chi square unbiased Risk Estimate for denoising magnitude mr images
International Conference on Image Processing, 2011Co-Authors: Florian Luisier, Patrick J. WolfeAbstract:In this article we develop Stein-type results for unbiased estimation of the Risk associated with parametric estimators of the noncentrality parameter of chi-squared random variables on two degrees of freedom. These results allow for estimator adaptivity, and thus can be used to optimize the parameters of a broad class of typical denoising functions, subject only to weak smoothness assumptions. We show how to apply these results to the problem of enhancing magnitude magnetic resonance images, which are known to be corrupted by Rician noise. As an example, we propose a transform-domain point-wise estimator based on linear expansion of thresholds. Finally, we apply this estimator to synthetic and real image data in conjunction with the undecimated Haar wavelet transform, and conclude that it is able to outperform previous wavelet-based techniques and compares favorably with a more recent approach based on non-local means.
-
image denoising in mixed poisson gaussian noise
IEEE Transactions on Image Processing, 2011Co-Authors: Florian Luisier, Thierry Blu, Michael UnserAbstract:We propose a general methodology (PURE-LET) to design and optimize a wide class of transform-domain thresholding algorithms for denoising images corrupted by mixed Poisson-Gaussian noise. We express the denoising process as a linear expansion of thresholds (LET) that we optimize by relying on a purely data-adaptive unbiased Estimate of the mean-squared error (MSE), derived in a non-Bayesian framework (PURE: Poisson-Gaussian unbiased Risk Estimate). We provide a practical approximation of this theoretical MSE Estimate for the tractable optimization of arbitrary transform-domain thresholding. We then propose a pointwise estimator for undecimated filterbank transforms, which consists of subband-adaptive thresholding functions with signal-dependent thresholds that are globally optimized in the image domain. We finally demonstrate the potential of the proposed approach through extensive comparisons with state-of-the-art techniques that are specifically tailored to the estimation of Poisson intensities. We also present denoising results obtained on real images of low-count fluorescence microscopy.
-
SUBMITTED MANUSCRIPT 1 A CURE for Noisy Magnetic Resonance Images: Chi-Square Unbiased Risk Estimation
2011Co-Authors: Florian Luisier, Thierry Blu, Patrick J. WolfeAbstract:In this article we derive an unbiased expression for the expected mean-squared error associated with continuously differentiable estimators of the noncentrality parameter of a chi-square random variable. We then consider the task of denoising squared-magnitude magnetic resonance image data, which are well modeled as independent noncentral chi-square random variables on two degrees of freedom. We consider two broad classes of linearly parameterized shrinkage estimators that can be optimized using our Risk Estimate, one in the general context of undecimated filterbank transforms, and another in the specific case of the unnormalized Haar wavelet transform. The resultant algorithms are computationally tractable and improve upon state-of-the-art methods for both simulated and actual magnetic resonance image data
Sylvain Sardy - One of the best experts on this subject based on the ideXlab platform.
-
smooth blockwise iterative thresholding a smooth fixed point estimator based on the likelihood s block gradient
Journal of the American Statistical Association, 2012Co-Authors: Sylvain SardyAbstract:The proposed smooth blockwise iterative thresholding estimator (SBITE) is a model selection technique defined as a fixed point reached by iterating a likelihood gradient-based thresholding function. The smooth James–Stein thresholding function has two regularization parameters λ and ν, and a smoothness parameter s. It enjoys smoothness like ridge regression and selects variables like lasso. Focusing on Gaussian regression, we show that SBITE is uniquely defined, and that its Stein unbiased Risk Estimate is a smooth function of λ and ν, for better selection of the two regularization parameters. We perform a Monte Carlo simulation to investigate the predictive and oracle properties of this smooth version of adaptive lasso. The motivation is a gravitational wave burst detection problem from several concomitant time series. A nonparametric wavelet-based estimator is developed to combine information from all captors by block-thresholding multiresolution coefficients. We study how the smoothness parameter s tem...
-
smooth blockwise iterative thresholding a smooth fixed point estimator based on the likelihood s block gradient
arXiv: Methodology, 2011Co-Authors: Sylvain SardyAbstract:The proposed smooth blockwise iterative thresholding estimator (SBITE) is a model selection technique defined as a fixed point reached by iterating a likelihood gradient-based thresholding function. The smooth James-Stein thresholding function has two regularization parameters $\lambda$ and $\nu$, and a smoothness parameter $s$. It enjoys smoothness like ridge regression and selects variables like lasso. Focusing on Gaussian regression, we show that SBITE is uniquely defined, and that its Stein unbiased Risk Estimate is a smooth function of $\lambda$ and $\nu$, for better selection of the two regularization parameters. We perform a Monte-Carlo simulation to investigate the predictive and oracle properties of this smooth version of adaptive lasso. The motivation is a gravitational wave burst detection problem from several concomitant time series. A nonparametric wavelet-based estimator is developed to combine information from all captors by block-thresholding multiresolution coefficients. We study how the smoothness parameter $s$ tempers the erraticity of the Risk Estimate, and derive a universal threshold, an information criterion and an oracle inequality in this canonical setting.
Chinglung Cheung - One of the best experts on this subject based on the ideXlab platform.
-
incidence and Risk Estimate of drug induced agranulocytosis in hong kong chinese a population based case control study
Pharmacoepidemiology and Drug Safety, 2017Co-Authors: Chorwing Sing, Chinglung Cheung, Ian C K Wong, Bernard M Y Cheung, Johnny C Y Chan, Jody K P ChuAbstract:Purpose Drug-induced agranulocytosis is a rare but life-threatening adverse drug reaction. Its epidemiology in Chinese is largely unknown. This study aimed to Estimate the incidence, mortality, and Risk of the drugs associated with agranulocytosis in Hong Kong Chinese. Methods A population-based case-control study was conducted using the Clinical Data Analysis and Reporting System, a database managed by the Hong Kong Hospital Authority. Patients with drug-induced agranulocytosis from 1 January 2004 to 31 December 2013 were identified. World Health Organization causality assessment was used to evaluate the possible drug aetiology of each case. Odd ratios (ORs) of the drug exposure were calculated using exact conditional logistic regression. Results 155 cases of drug-induced agranulocytosis were identified. Mean age was 51.4 years and 95 cases were female. Incidence rate was Estimated to be 2.2 cases per million person-years and the all-cause mortality of patients with drug-induced agranulocytosis was 3.9%. Among the cases, the most common associated drug groups were antithyroid drugs (41.9%), antimicrobials (20%), anticonvulsants (10.3%), and antipsychotics (6.5%). Carbimazole had the highest Risk of agranulocytosis (adjusted OR 416.7, 95% Confidence Interval (CI) 51.5 – 3372.9) with an incidence of 9.2 (95% CI 6.9 - 12.1) per 10,000 users and 3.6 (95% CI 2.7 - 4.8) per 10,000 user-years. Other drugs with significant Risk included cephalosporins, clozapine, penicillins, phenytoin, and propyl thiouracil. Conclusions The incidence and mortality in Hong Kong Chinese were relatively low compared to Caucasians. Antithyroid drugs were the most common Its epidemiology in Chinese is largely unknown. This study aimed to Estimate the incidence, mortality, and Risk of the drugs associated with agranulocytosis in Hong Kong Chinese. Methods A population-based case-control study was conducted using the Clinical Data Analysis and Reporting System, a database managed by the Hong Kong Hospital Authority. Patients with drug-induced agranulocytosis from 1 January 2004 to 31 December 2013 were identified. World Health Organization causality assessment was used to evaluate the possible drug aetiology of each case. Odd ratios (ORs) of the drug exposure were calculated using exact conditional logistic regression. Results 155 cases of drug-induced agranulocytosis were identified. Mean age was 51.4 years and 95 cases were female. Incidence rate was Estimated to be 2.2 cases per million person-years and the all-cause mortality of patients with drug-induced agranulocytosis was 3.9%. Among the cases, the most common associated drug groups were antithyroid drugs (41.9%), antimicrobials (20%), anticonvulsants (10.3%), and antipsychotics (6.5%). Carbimazole had the highest Risk of agranulocytosis (adjusted OR 416.7, 95% Confidence Interval (CI) 51.5 – 3372.9) with an incidence of 9.2 (95% CI 6.9 - 12.1) per 10,000 users and 3.6 (95% CI 2.7 - 4.8) per 10,000 user-years. Other drugs with significant Risk included cephalosporins, clozapine, penicillins, phenytoin, and propyl thiouracil. Conclusions The incidence and mortality in Hong Kong Chinese were relatively low compared to Caucasians. Antithyroid drugs were the most common implicated drug class and carbimazole had the highest Risk of agranulocytosis.
Jeffrey A Fessler - One of the best experts on this subject based on the ideXlab platform.
-
monte carlo sure based parameter selection for parallel magnetic resonance imaging reconstruction
Magnetic Resonance in Medicine, 2014Co-Authors: Daniel S Weller, Sathish Ramani, Jon Fredrik Nielsen, Jeffrey A FesslerAbstract:Purpose Regularizing parallel magnetic resonance imaging (MRI) reconstruction significantly improves image quality but requires tuning parameter selection. We propose a Monte Carlo method for automatic parameter selection based on Stein's unbiased Risk Estimate that minimizes the multichannel k-space mean squared error (MSE). We automatically tune parameters for image reconstruction methods that preserve the undersampled acquired data, which cannot be accomplished using existing techniques. Theory We derive a weighted MSE criterion appropriate for data-preserving regularized parallel imaging reconstruction and the corresponding weighted Stein's unbiased Risk Estimate. We describe a Monte Carlo approximation of the weighted Stein's unbiased Risk Estimate that uses two evaluations of the reconstruction method per candidate parameter value. Methods We reconstruct images using the denoising sparse images from GRAPPA using the nullspace method (DESIGN) and L1 iterative self-consistent parallel imaging (L1-SPIRiT). We validate Monte Carlo Stein's unbiased Risk Estimate against the weighted MSE. We select the regularization parameter using these methods for various noise levels and undersampling factors and compare the results to those using MSE-optimal parameters. Results Our method selects nearly MSE-optimal regularization parameters for both DESIGN and L1-SPIRiT over a range of noise levels and undersampling factors. Conclusion The proposed method automatically provides nearly MSE-optimal choices of regularization parameters for data-preserving nonlinear parallel MRI reconstruction methods. Magn Reson Med 71:1760–1770, 2014. © 2013 Wiley Periodicals, Inc.
