The Experts below are selected from a list of 129 Experts worldwide ranked by ideXlab platform
Mahnaz Shahidi - One of the best experts on this subject based on the ideXlab platform.
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Direct Regularized Estimation of Retinal Vascular Oxygen Tension Based on an Experimental Model
Annals of Biomedical Engineering, 2013Co-Authors: Isa Yildirim, Rashid Ansari, I. Samil Yetik, Mahnaz ShahidiAbstract:Phosphorescence lifetime imaging is commonly used to generate Oxygen Tension maps of retinal blood vessels by classical least squares (LS) estimation method. A spatial regularization method was later proposed and provided improved results. However, both methods obtain Oxygen Tension values from the estimates of intermediate variables, and do not yield an optimum estimate of Oxygen Tension values, due to their nonlinear dependence on the ratio of intermediate variables. In this paper, we provide an improved solution by devising a regularized direct least squares (RDLS) method that exploits available knowledge in studies that provide models of Oxygen Tension in retinal arteries and veins, unlike the earlier regularized LS approach where knowledge about intermediate variables is limited. The performance of the proposed RDLS method is evaluated by investigating and comparing the bias, variance, Oxygen Tension maps, 1-D profiles of arterial Oxygen Tension, and mean absolute error with those of earlier methods, and its superior performance both quantitatively and qualitatively is demonstrated.
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ISBI - Estimation of Oxygen Tension in retinal capillaries from phosphorescence lifetime images
2009 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2009Co-Authors: Isa Yildirim, I. Samil Yetik, Justin Wanek, Rashid Ansari, Mahnaz ShahidiAbstract:Investigating the effect of retinal Oxygenation abnormalities in the development of common eye diseases requires accurate assessment of Oxygen Tension in retinal vasculatures. Estimation of Oxygen Tension in retinal capillaries using phosphorescence lifetime imaging is addressed in this paper. Separation from tissue and Oxygen Tension estimation is a more challenging task for capillaries when compared with large retinal vessels due to the finer structure and noise predominance in capillaries. An automated segmentation procedure is applied using the EM algorithm and noise contamination is reduced using a regularization method unlike previous approaches to capillary analysis where segmentation was done manually and noise contamination was ignored. We demonstrate the effectiveness of the proposed method by applying it to the retinal image data acquired from rat eyes, and we show that the Oxygen Tension estimate of retinal capillaries falls in the physiologically expected range.
Isa Yildirim - One of the best experts on this subject based on the ideXlab platform.
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Direct Regularized Estimation of Retinal Vascular Oxygen Tension Based on an Experimental Model
Annals of Biomedical Engineering, 2013Co-Authors: Isa Yildirim, Rashid Ansari, I. Samil Yetik, Mahnaz ShahidiAbstract:Phosphorescence lifetime imaging is commonly used to generate Oxygen Tension maps of retinal blood vessels by classical least squares (LS) estimation method. A spatial regularization method was later proposed and provided improved results. However, both methods obtain Oxygen Tension values from the estimates of intermediate variables, and do not yield an optimum estimate of Oxygen Tension values, due to their nonlinear dependence on the ratio of intermediate variables. In this paper, we provide an improved solution by devising a regularized direct least squares (RDLS) method that exploits available knowledge in studies that provide models of Oxygen Tension in retinal arteries and veins, unlike the earlier regularized LS approach where knowledge about intermediate variables is limited. The performance of the proposed RDLS method is evaluated by investigating and comparing the bias, variance, Oxygen Tension maps, 1-D profiles of arterial Oxygen Tension, and mean absolute error with those of earlier methods, and its superior performance both quantitatively and qualitatively is demonstrated.
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ISBI - Map estimation of Oxygen Tension in retinal vessels with phosphorescence lifetime imaging
2012 9th IEEE International Symposium on Biomedical Imaging (ISBI), 2012Co-Authors: Isa Yildirim, Rashid AnsariAbstract:In phosphorescence lifetime imaging methods Oxygen Tension in retinal vessels has traditionally been indirectly determined from the estimates of intermediate variables whose noise-contaminated linear combinations are observed as phosphorescence intensity images. The classical least squares (LS) and regularized least squares (RLS) methods were used to obtain estimates of the intermediate variables. The estimates of the intermediate variables are then used to compute Oxygen Tension. The estimates of intermediate variables, however, do not yield an optimum estimate of Oxygen Tension due to its nonlinear dependence on the ratio of intermediate variables. Moreover, prior knowledge about the variables is very limited so that the level of noise cannot be reliably estimated, thereby affecting the automated choice of the regularization parameter in the RLS method. In this study the problem of optimally estimating Oxygen Tension in retinal vessels using the maximum a posteriori (MAP) criterion is addressed. For this purpose the conditional distribution of Oxygen Tension is derived given the phosphorescence lifetime imaging observations and model. The performance of MAP is compared with that of LS and the RLS methods using simulated data and its improved performance in the presence of different levels of noise is demonstrated.
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ISBI - Estimation of Oxygen Tension in retinal capillaries from phosphorescence lifetime images
2009 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2009Co-Authors: Isa Yildirim, I. Samil Yetik, Justin Wanek, Rashid Ansari, Mahnaz ShahidiAbstract:Investigating the effect of retinal Oxygenation abnormalities in the development of common eye diseases requires accurate assessment of Oxygen Tension in retinal vasculatures. Estimation of Oxygen Tension in retinal capillaries using phosphorescence lifetime imaging is addressed in this paper. Separation from tissue and Oxygen Tension estimation is a more challenging task for capillaries when compared with large retinal vessels due to the finer structure and noise predominance in capillaries. An automated segmentation procedure is applied using the EM algorithm and noise contamination is reduced using a regularization method unlike previous approaches to capillary analysis where segmentation was done manually and noise contamination was ignored. We demonstrate the effectiveness of the proposed method by applying it to the retinal image data acquired from rat eyes, and we show that the Oxygen Tension estimate of retinal capillaries falls in the physiologically expected range.
Einar Stefánsson - One of the best experts on this subject based on the ideXlab platform.
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Optic nerve Oxygen Tension : effects of intraocular pressure and dorzolamide
The British journal of ophthalmology, 2000Co-Authors: M. La Cour, Jens Folke Kiilgaard, Thor Eysteinsson, Anne Katrine Wiencke, K Bang, Jens Dollerup, Peter Koch Jensen, Einar StefánssonAbstract:AIM—To investigate the influence of acute changes in intraocular pressure on the Oxygen Tension in the vicinity of the optic nerve head under control conditions and after intravenous administration of 500 mg of the carbonic anhydrase inhibitor dorzolamide. METHODS—Domestic pigs were used as experimental animals. Oxygen Tension was measured by means of a polarographic electrode in the vitreous 0.5 mm anterior to the optic disc. This entity is called the optic nerve Oxygen Tension. Intraocular pressure was controlled by a hypodermic needle inserted into the anterior chamber and connected to a saline reservoir. RESULTS—When the intraocular pressure was clamped at 20 cm H2O optic nerve Oxygen Tension was 20 (5) mm Hg (n=8). Intravenous administration of dorzolamide caused an increase in optic nerve Oxygen Tension of 43 (8)% (n=6). Both before and after administration of dorzolamide optic nerve Oxygen Tension was unaffected by changes in intraocular pressure, as long as this pressure remained below 60 cm H2O. At intraocular pressures of 60 cm H2O and below, dorzolamide significantly increased optic nerve Oxygen Tension. CONCLUSION—Intravenous administration of 500 mg dorzolamide increases the Oxygen Tension at the optic nerve head during acute increases in intraocular pressure.
Rashid Ansari - One of the best experts on this subject based on the ideXlab platform.
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Direct Regularized Estimation of Retinal Vascular Oxygen Tension Based on an Experimental Model
Annals of Biomedical Engineering, 2013Co-Authors: Isa Yildirim, Rashid Ansari, I. Samil Yetik, Mahnaz ShahidiAbstract:Phosphorescence lifetime imaging is commonly used to generate Oxygen Tension maps of retinal blood vessels by classical least squares (LS) estimation method. A spatial regularization method was later proposed and provided improved results. However, both methods obtain Oxygen Tension values from the estimates of intermediate variables, and do not yield an optimum estimate of Oxygen Tension values, due to their nonlinear dependence on the ratio of intermediate variables. In this paper, we provide an improved solution by devising a regularized direct least squares (RDLS) method that exploits available knowledge in studies that provide models of Oxygen Tension in retinal arteries and veins, unlike the earlier regularized LS approach where knowledge about intermediate variables is limited. The performance of the proposed RDLS method is evaluated by investigating and comparing the bias, variance, Oxygen Tension maps, 1-D profiles of arterial Oxygen Tension, and mean absolute error with those of earlier methods, and its superior performance both quantitatively and qualitatively is demonstrated.
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ISBI - Map estimation of Oxygen Tension in retinal vessels with phosphorescence lifetime imaging
2012 9th IEEE International Symposium on Biomedical Imaging (ISBI), 2012Co-Authors: Isa Yildirim, Rashid AnsariAbstract:In phosphorescence lifetime imaging methods Oxygen Tension in retinal vessels has traditionally been indirectly determined from the estimates of intermediate variables whose noise-contaminated linear combinations are observed as phosphorescence intensity images. The classical least squares (LS) and regularized least squares (RLS) methods were used to obtain estimates of the intermediate variables. The estimates of the intermediate variables are then used to compute Oxygen Tension. The estimates of intermediate variables, however, do not yield an optimum estimate of Oxygen Tension due to its nonlinear dependence on the ratio of intermediate variables. Moreover, prior knowledge about the variables is very limited so that the level of noise cannot be reliably estimated, thereby affecting the automated choice of the regularization parameter in the RLS method. In this study the problem of optimally estimating Oxygen Tension in retinal vessels using the maximum a posteriori (MAP) criterion is addressed. For this purpose the conditional distribution of Oxygen Tension is derived given the phosphorescence lifetime imaging observations and model. The performance of MAP is compared with that of LS and the RLS methods using simulated data and its improved performance in the presence of different levels of noise is demonstrated.
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ISBI - Estimation of Oxygen Tension in retinal capillaries from phosphorescence lifetime images
2009 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2009Co-Authors: Isa Yildirim, I. Samil Yetik, Justin Wanek, Rashid Ansari, Mahnaz ShahidiAbstract:Investigating the effect of retinal Oxygenation abnormalities in the development of common eye diseases requires accurate assessment of Oxygen Tension in retinal vasculatures. Estimation of Oxygen Tension in retinal capillaries using phosphorescence lifetime imaging is addressed in this paper. Separation from tissue and Oxygen Tension estimation is a more challenging task for capillaries when compared with large retinal vessels due to the finer structure and noise predominance in capillaries. An automated segmentation procedure is applied using the EM algorithm and noise contamination is reduced using a regularization method unlike previous approaches to capillary analysis where segmentation was done manually and noise contamination was ignored. We demonstrate the effectiveness of the proposed method by applying it to the retinal image data acquired from rat eyes, and we show that the Oxygen Tension estimate of retinal capillaries falls in the physiologically expected range.
P.-o. Carlsson - One of the best experts on this subject based on the ideXlab platform.
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Reactive Oxygen species cause diabetes-induced decrease in renal Oxygen Tension
Diabetologia, 2003Co-Authors: F. Palm, J. Cederberg, P. Hansell, P. Liss, P.-o. CarlssonAbstract:Aims/hypothesis Augmented formation of reactive Oxygen species (ROS) induced by hyperglycaemia has been suggested to contribute to the development of diabetic nephropathy. This study was designed to evaluate the influence of streptozotocin (STZ)-induced diabetes mellitus, as well as the effects of preventing excessive ROS formation by α-tocopherol treatment, on regional renal blood flow, Oxygen Tension and Oxygen consumption in anaesthetized Wistar Furth rats. Methods Non-diabetic and STZ-diabetic rats were investigated after 4 weeks with or without dietary treatment with the radical scavenger DL-α-tocopherol (vitamin E, 5%). A laser-Doppler technique was used to measure regional renal blood flow, whilst Oxygen Tension and consumption were measured using Clark-type microelectrodes. Results Renal Oxygen Tension, but not renal blood flow, was lower throughout the renal parenchyma of diabetic rats when compared to non-diabetic control rats. The decrease in Oxygen Tension was most pronounced in the renal medulla. Renal cellular Oxygen consumption was markedly increased in diabetic rats, predominantly in the medullary region. Diabetes increased lipid peroxidation and protein carbonylation in the renal medulla. Treatment with α-tocopherol throughout the course of diabetes prevented diabetes-induced disturbances in oxidative stress, Oxygen Tension and consumption. The diabetic animals had a renal hypertrophy and a glomerular hyperfiltration, which were unaffected by α-tocopherol treatment. Conclusions/interpretation We conclude that oxidative stress occurs in kidneys of diabetic rats predominantly in the medullary region and relates to augmented Oxygen consumption and impaired Oxygen Tension in the tissue.
