Browsing by Author "Baradaran, H."

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Speckle reduction in medical ultrasound images using an unbiased non-local means method
(2016) Sudeep, P.V.; Palanisamy, P.; Rajan, J.; Baradaran, H.; Saba, L.; Gupta, A.; Suri, J.S.
Enhancement of ultrasound (US) images is required for proper visual inspection and further pre-processing since US images are generally corrupted with speckle. In this paper, a new approach based on non-local means (NLM) method is proposed to remove the speckle noise in the US images. Since the interpolated final Cartesian image produced from uncompressed ultrasound data contaminated with fully developed speckle can be represented by a Gamma distribution, a Gamma model is incorporated in the proposed denoising procedure. In addition, the scale and shape parameters of the Gamma distribution are estimated using the maximum likelihood (ML) method. Bias due to speckle noise is expressed using these parameters and is removed from the NLM filtered output. The experiments on phantom images and real 2D ultrasound datasets show that the proposed method outperforms other related well-accepted methods, both in terms of objective and subjective evaluations. The results demonstrate that the proposed method has a better performance in both speckle reduction and preservation of structural features. 2016 Elsevier Ltd. All rights reserved.
Speckle reduction in medical ultrasound images using an unbiased non-local means method
(Elsevier Ltd, 2016) Sudeep, P.V.; Ponnusamy, P.; Rajan, J.; Baradaran, H.; Saba, L.; Gupta, A.; Suri, J.S.
Enhancement of ultrasound (US) images is required for proper visual inspection and further pre-processing since US images are generally corrupted with speckle. In this paper, a new approach based on non-local means (NLM) method is proposed to remove the speckle noise in the US images. Since the interpolated final Cartesian image produced from uncompressed ultrasound data contaminated with fully developed speckle can be represented by a Gamma distribution, a Gamma model is incorporated in the proposed denoising procedure. In addition, the scale and shape parameters of the Gamma distribution are estimated using the maximum likelihood (ML) method. Bias due to speckle noise is expressed using these parameters and is removed from the NLM filtered output. The experiments on phantom images and real 2D ultrasound datasets show that the proposed method outperforms other related well-accepted methods, both in terms of objective and subjective evaluations. The results demonstrate that the proposed method has a better performance in both speckle reduction and preservation of structural features. © 2016 Elsevier Ltd. All rights reserved.
Wall shear stress and oscillatory shear index distribution in carotid artery with varying degree of stenosis: A hemodynamic study
(2017) Basavaraja, P.; Surendran, A.; Gupta, A.; Saba, L.; Laird, J.R.; Nicolaides, A.; Mtui, E.E.; Baradaran, H.; Lavra, F.; Suri, J.S.
A significant proportion of cerebral stroke is a consequence of the arterial stenotic plaque rupture causing local thrombosis or distal embolization. The formation and subsequent rupture of the plaque depends on wall shear stress (WSS) and oscillatory shear index (OSI). The purpose of the present study was to understand the effect of hemodynamics on the spatial and temporal variations of WSS and OSI using realistic models with varying degree of carotid artery stenosis (DOS). Multiple CT volumes were obtained from subjects in the carotid bifurcation zone and the 3D models were generated. A finite volume-based computational fluid dynamics (CFD) method was utilized to understand the hemodynamics in pulsatile flow conditions. It was observed that high stenosis models occupied a large value of normalized WSS in the internal carotid artery (ICA) whereas they had smaller values of normalized WSS in the common carotid artery (CCA). For clinical use, the authors recommend using the spatial average value of oscillatory shear rather than the maximum value for an accurate knowledge about the severity of stenosis. The resultant vorticity changes the direction of spin after the bifurcation zone. Additionally, we propose the use of limiting streamlines as a novel and convenient method to identify the disturbed flow regions that are prone to atherogenesis. � 2017 World Scientific Publishing Company.
Wall shear stress and oscillatory shear index distribution in carotid artery with varying degree of stenosis: A hemodynamic study
(World Scientific Publishing Co. Pte Ltd wspc@wspc.com.sg, 2017) Basavaraja, P.; Anish, S.; Gupta, A.; Saba, L.; Laird, J.R.; Nicolaïdes, A.; Mtui, E.E.; Baradaran, H.; Lavra, F.; Suri, J.S.
A significant proportion of cerebral stroke is a consequence of the arterial stenotic plaque rupture causing local thrombosis or distal embolization. The formation and subsequent rupture of the plaque depends on wall shear stress (WSS) and oscillatory shear index (OSI). The purpose of the present study was to understand the effect of hemodynamics on the spatial and temporal variations of WSS and OSI using realistic models with varying degree of carotid artery stenosis (DOS). Multiple CT volumes were obtained from subjects in the carotid bifurcation zone and the 3D models were generated. A finite volume-based computational fluid dynamics (CFD) method was utilized to understand the hemodynamics in pulsatile flow conditions. It was observed that high stenosis models occupied a large value of normalized WSS in the internal carotid artery (ICA) whereas they had smaller values of normalized WSS in the common carotid artery (CCA). For clinical use, the authors recommend using the spatial average value of oscillatory shear rather than the maximum value for an accurate knowledge about the severity of stenosis. The resultant vorticity changes the direction of spin after the bifurcation zone. Additionally, we propose the use of limiting streamlines as a novel and convenient method to identify the disturbed flow regions that are prone to atherogenesis. © 2017 World Scientific Publishing Company.