T. Varghese - Academia.edu (original) (raw)
Papers by T. Varghese
Journal of Clinical and Experimental Hepatology, 2011
The 23rd Digital Avionics Systems Conference (IEEE Cat. No.04CH37576), 2004
Journal of Virology, 2001
ie gene expression, including TNF and NF-B. Allogeneic transplantation combined with immunosuppre... more ie gene expression, including TNF and NF-B. Allogeneic transplantation combined with immunosuppression may be required to achieve complete reactivation in vivo.
Journal of child neurology, 2003
A prospective study of Guillain-Barré syndrome from January 1992 to December 2001 was undertaken.... more A prospective study of Guillain-Barré syndrome from January 1992 to December 2001 was undertaken. Intravenous immunoglobulins were used in all patients. All patients were followed up until complete recovery. Various parameters, such as onset of weakness, duration of hospital stay, ventilation requirement, residual deficit, and mortality, were recorded. Acute relapses and fluctuations were also noted. The pattern of this group was compared with patients before 1992, who were not given intravenous immunoglobulins in the Sultanate of Oman. Our data were compared with a few studies prior to 1992 from the medical literature. Our study revealed a definite benefit with intravenous immunoglobulins. The disease course and hospital stay were shortened. Fewer patients needed ventilation. There was no mortality, and the residual deficit was less than 5%. Occasional relapses at a later stage in the course of illness have been noted in acute Guillain-Barré syndrome. However, acute relapse, a new ...
IEEE Ultrasonics Symposium, 2004, 2004
Delineation of RF-ablator induced coagulation (thermal lesion) boundaries is an important clinica... more Delineation of RF-ablator induced coagulation (thermal lesion) boundaries is an important clinical problem not well addressed by conventional imaging modalities. Automation of this process is certainly desirable. Elastography that estimates and images the local strain corresponding to small, externally applied, quasi-static compressions can be used for visualization of thermal coagulations. Several studies have demonstrated that coagulation volumes computed from multiple planar slices through the region of interest are more accurate than volumes estimated assuming simple shapes and incorporating single or orthogonal diameter estimates. This paper presents an automated segmentation approach for thermal coagulations on three-dimensional elastographic data to obtain both area and volume information. This approach consists of a coarse-to-fine method for active contour initialization and a gradient vector flow active contour model for deformable contour optimization with the help of prior knowledge of the geometry of general thermal coagulations.
1997 IEEE Ultrasonics Symposium Proceedings. An International Symposium (Cat. No.97CH36118), 1997
The authors analyze the performance of multiresolution elastography, where the strain estimate wi... more The authors analyze the performance of multiresolution elastography, where the strain estimate with the highest elastographic signal-to-noise ratio (SNRe) obtained by processing the pre- and post-compression waveforms at different window lengths. All the objective elastographic parameters, namely: SNRe, sensitivity dynamic range and the average resolution (defined as the cross-correlation window length) are improved with multiresolution elastography when compared to the
2007 IEEE Ultrasonics Symposium Proceedings, 2007
Strain and strain rate imaging provide new information for evaluation of regional myocardial func... more Strain and strain rate imaging provide new information for evaluation of regional myocardial function. Clinical diagnosis using echocardiography is based on visually assessed wall motion scoring, which is semi quantitative and heavily weighted on operator experience and expertise. Cardiac motion estimation methods such as Tissue Doppler and elastography can be used to assess myocardial muscle displacements, providing quantitative parameters such
Ultrasonic imaging, Jan 28, 2015
Plaque instability may lead to chronic embolization, which in turn may contribute to progressive ... more Plaque instability may lead to chronic embolization, which in turn may contribute to progressive cognitive decline. Accumulated strain tensor indices over a cardiac cycle within a pulsating carotid plaque may be viable biomarkers for the diagnosis of plaque instability. Using plaque-only carotid artery segmentations, we recently demonstrated that impaired cognitive function correlated significantly with maximum axial and lateral strain indices within a localized region of interest in plaque. Inclusion of the adventitial layer focuses our strain or instability measures on the vessel wall-plaque interface hypothesized to be a region with increased shearing forces and measureable instability. A hierarchical block-matching motion tracking algorithm developed in our laboratory was used to estimate accumulated axial, lateral, and shear strain distribution in plaques identified with the plaque-with-adventitia segmentation. Correlations of strain indices to the Repeatable Battery for the As...
Ultrasound in medicine & biology, 2004
Several studies have demonstrated that lesion volumes computed from multiple planar slices throug... more Several studies have demonstrated that lesion volumes computed from multiple planar slices through the region-of-interest (ROI) are more accurate than volumes estimated assuming simple shapes and incorporating single or orthogonal diameter estimates. However, manual delineation of boundaries on multiple planar 2-D images is tedious and labor-intensive. Automatic extraction of lesion boundaries is, therefore, attractive and imperative to remove subjectivity and reduce assessment time. This paper presents a semiautomated segmentation algorithm for thermal lesions on 3-D elastographic data to obtain both area and volume information. The semiautomated segmentation algorithm is based on thresholding and morphologic opening of both 2-D and 3-D elastographic data. Results obtained on 44 thermal lesions imaged in vitro using elastography were compared to manual delineation of both elastographic and pathology images. Results obtained using semiautomated segmentation demonstrate a close corre...
Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine, 2012
In this article, we demonstrate the feasibility of saline infusion sonohysterography-based strain... more In this article, we demonstrate the feasibility of saline infusion sonohysterography-based strain imaging for the determination of stiffness variations in uterine masses in vivo. Strain images are estimated using a 2-dimensional multilevel hybrid algorithm developed for sector array ultrasound transducers. Coarse displacements are initially estimated using envelope echo signals, followed by a guided finer displacement estimation using window lengths on the order of 6 wavelengths and 7 A-lines on radiofrequency data. Strain images are obtained by estimating displacement slopes using least squares estimation. In this prospective study, we show that stiffer masses such as fibroids appear darker or as regions with low strain on strain images and are thus clearly differentiated when compared to normal uterine tissue. A high strain boundary around stiffer masses referred to as a "halo" due to increased slipping or sliding of the mass during the applied deformation is also visual...
Ultrasound in medicine & biology, 2007
In current ultrasound elastography, only the axial component of the displacement vector is estima... more In current ultrasound elastography, only the axial component of the displacement vector is estimated and used to produce strain images. A method was recently proposed by our group to estimate both the axial and lateral components of a displacement vector following a uniaxial compression. Previous work evaluated the technique using both simulations and a mechanically translated phased array transducer. In this paper, we present initial results using beam steering on a linear array transducer attached to a commercial scanner to acquire echo signals for estimating 2-D displacement vectors. Single-inclusion and anthropomorphic breast phantoms with different boundary properties between the inclusion and background material are imaged by acquiring echo data along beam lines ranging from -15 degrees to 15 degrees relative to the compression direction. 1-D cross-correlation is used to calculate "angular displacements" in each acquisition direction, yielding axial and lateral compo...
Ultrasonic imaging, 2001
This paper presents the tradeoffs in elastographic imaging. Elastography is viewed as a new imagi... more This paper presents the tradeoffs in elastographic imaging. Elastography is viewed as a new imaging modality and presented in terms of three fundamental concepts that constitute the basis for the elastographic imaging process. These are the tissue elastic deformation process, the statistical analysis of strain estimation and the image characterization. The first concept involves the use of the contrast transfer efficiency (CTE) that describes the mapping of a distribution of local tissue elastic moduli into a distribution of local longitudinal tissue strains. The second concept defines the elastographic system and the relationship between ultrasonic and signal processing parameters. This process is described in terms of a stochastic framework (the strain filter) that provides upper and practical performance bounds and their dependence on the various system parameters. Finally, the output image, the elastogram, is characterized by its image parameters, such as signal-to-noise ratio, ...
2006 IEEE Ultrasonics Symposium, 2006
Page 1. Ultrasound Simulation of Real-Time Temperature Estimation during Radiofrequency Ablation ... more Page 1. Ultrasound Simulation of Real-Time Temperature Estimation during Radiofrequency Ablation using Finite Element Models Matthew J. Daniels University of Wisconsin Madison Physics Madison, USA mjdaniels@wisc.edu ...
2011 IEEE International Ultrasonics Symposium, 2011
Journal of Clinical and Experimental Hepatology, 2011
The 23rd Digital Avionics Systems Conference (IEEE Cat. No.04CH37576), 2004
Journal of Virology, 2001
ie gene expression, including TNF and NF-B. Allogeneic transplantation combined with immunosuppre... more ie gene expression, including TNF and NF-B. Allogeneic transplantation combined with immunosuppression may be required to achieve complete reactivation in vivo.
Journal of child neurology, 2003
A prospective study of Guillain-Barré syndrome from January 1992 to December 2001 was undertaken.... more A prospective study of Guillain-Barré syndrome from January 1992 to December 2001 was undertaken. Intravenous immunoglobulins were used in all patients. All patients were followed up until complete recovery. Various parameters, such as onset of weakness, duration of hospital stay, ventilation requirement, residual deficit, and mortality, were recorded. Acute relapses and fluctuations were also noted. The pattern of this group was compared with patients before 1992, who were not given intravenous immunoglobulins in the Sultanate of Oman. Our data were compared with a few studies prior to 1992 from the medical literature. Our study revealed a definite benefit with intravenous immunoglobulins. The disease course and hospital stay were shortened. Fewer patients needed ventilation. There was no mortality, and the residual deficit was less than 5%. Occasional relapses at a later stage in the course of illness have been noted in acute Guillain-Barré syndrome. However, acute relapse, a new ...
IEEE Ultrasonics Symposium, 2004, 2004
Delineation of RF-ablator induced coagulation (thermal lesion) boundaries is an important clinica... more Delineation of RF-ablator induced coagulation (thermal lesion) boundaries is an important clinical problem not well addressed by conventional imaging modalities. Automation of this process is certainly desirable. Elastography that estimates and images the local strain corresponding to small, externally applied, quasi-static compressions can be used for visualization of thermal coagulations. Several studies have demonstrated that coagulation volumes computed from multiple planar slices through the region of interest are more accurate than volumes estimated assuming simple shapes and incorporating single or orthogonal diameter estimates. This paper presents an automated segmentation approach for thermal coagulations on three-dimensional elastographic data to obtain both area and volume information. This approach consists of a coarse-to-fine method for active contour initialization and a gradient vector flow active contour model for deformable contour optimization with the help of prior knowledge of the geometry of general thermal coagulations.
1997 IEEE Ultrasonics Symposium Proceedings. An International Symposium (Cat. No.97CH36118), 1997
The authors analyze the performance of multiresolution elastography, where the strain estimate wi... more The authors analyze the performance of multiresolution elastography, where the strain estimate with the highest elastographic signal-to-noise ratio (SNRe) obtained by processing the pre- and post-compression waveforms at different window lengths. All the objective elastographic parameters, namely: SNRe, sensitivity dynamic range and the average resolution (defined as the cross-correlation window length) are improved with multiresolution elastography when compared to the
2007 IEEE Ultrasonics Symposium Proceedings, 2007
Strain and strain rate imaging provide new information for evaluation of regional myocardial func... more Strain and strain rate imaging provide new information for evaluation of regional myocardial function. Clinical diagnosis using echocardiography is based on visually assessed wall motion scoring, which is semi quantitative and heavily weighted on operator experience and expertise. Cardiac motion estimation methods such as Tissue Doppler and elastography can be used to assess myocardial muscle displacements, providing quantitative parameters such
Ultrasonic imaging, Jan 28, 2015
Plaque instability may lead to chronic embolization, which in turn may contribute to progressive ... more Plaque instability may lead to chronic embolization, which in turn may contribute to progressive cognitive decline. Accumulated strain tensor indices over a cardiac cycle within a pulsating carotid plaque may be viable biomarkers for the diagnosis of plaque instability. Using plaque-only carotid artery segmentations, we recently demonstrated that impaired cognitive function correlated significantly with maximum axial and lateral strain indices within a localized region of interest in plaque. Inclusion of the adventitial layer focuses our strain or instability measures on the vessel wall-plaque interface hypothesized to be a region with increased shearing forces and measureable instability. A hierarchical block-matching motion tracking algorithm developed in our laboratory was used to estimate accumulated axial, lateral, and shear strain distribution in plaques identified with the plaque-with-adventitia segmentation. Correlations of strain indices to the Repeatable Battery for the As...
Ultrasound in medicine & biology, 2004
Several studies have demonstrated that lesion volumes computed from multiple planar slices throug... more Several studies have demonstrated that lesion volumes computed from multiple planar slices through the region-of-interest (ROI) are more accurate than volumes estimated assuming simple shapes and incorporating single or orthogonal diameter estimates. However, manual delineation of boundaries on multiple planar 2-D images is tedious and labor-intensive. Automatic extraction of lesion boundaries is, therefore, attractive and imperative to remove subjectivity and reduce assessment time. This paper presents a semiautomated segmentation algorithm for thermal lesions on 3-D elastographic data to obtain both area and volume information. The semiautomated segmentation algorithm is based on thresholding and morphologic opening of both 2-D and 3-D elastographic data. Results obtained on 44 thermal lesions imaged in vitro using elastography were compared to manual delineation of both elastographic and pathology images. Results obtained using semiautomated segmentation demonstrate a close corre...
Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine, 2012
In this article, we demonstrate the feasibility of saline infusion sonohysterography-based strain... more In this article, we demonstrate the feasibility of saline infusion sonohysterography-based strain imaging for the determination of stiffness variations in uterine masses in vivo. Strain images are estimated using a 2-dimensional multilevel hybrid algorithm developed for sector array ultrasound transducers. Coarse displacements are initially estimated using envelope echo signals, followed by a guided finer displacement estimation using window lengths on the order of 6 wavelengths and 7 A-lines on radiofrequency data. Strain images are obtained by estimating displacement slopes using least squares estimation. In this prospective study, we show that stiffer masses such as fibroids appear darker or as regions with low strain on strain images and are thus clearly differentiated when compared to normal uterine tissue. A high strain boundary around stiffer masses referred to as a "halo" due to increased slipping or sliding of the mass during the applied deformation is also visual...
Ultrasound in medicine & biology, 2007
In current ultrasound elastography, only the axial component of the displacement vector is estima... more In current ultrasound elastography, only the axial component of the displacement vector is estimated and used to produce strain images. A method was recently proposed by our group to estimate both the axial and lateral components of a displacement vector following a uniaxial compression. Previous work evaluated the technique using both simulations and a mechanically translated phased array transducer. In this paper, we present initial results using beam steering on a linear array transducer attached to a commercial scanner to acquire echo signals for estimating 2-D displacement vectors. Single-inclusion and anthropomorphic breast phantoms with different boundary properties between the inclusion and background material are imaged by acquiring echo data along beam lines ranging from -15 degrees to 15 degrees relative to the compression direction. 1-D cross-correlation is used to calculate "angular displacements" in each acquisition direction, yielding axial and lateral compo...
Ultrasonic imaging, 2001
This paper presents the tradeoffs in elastographic imaging. Elastography is viewed as a new imagi... more This paper presents the tradeoffs in elastographic imaging. Elastography is viewed as a new imaging modality and presented in terms of three fundamental concepts that constitute the basis for the elastographic imaging process. These are the tissue elastic deformation process, the statistical analysis of strain estimation and the image characterization. The first concept involves the use of the contrast transfer efficiency (CTE) that describes the mapping of a distribution of local tissue elastic moduli into a distribution of local longitudinal tissue strains. The second concept defines the elastographic system and the relationship between ultrasonic and signal processing parameters. This process is described in terms of a stochastic framework (the strain filter) that provides upper and practical performance bounds and their dependence on the various system parameters. Finally, the output image, the elastogram, is characterized by its image parameters, such as signal-to-noise ratio, ...
2006 IEEE Ultrasonics Symposium, 2006
Page 1. Ultrasound Simulation of Real-Time Temperature Estimation during Radiofrequency Ablation ... more Page 1. Ultrasound Simulation of Real-Time Temperature Estimation during Radiofrequency Ablation using Finite Element Models Matthew J. Daniels University of Wisconsin Madison Physics Madison, USA mjdaniels@wisc.edu ...
2011 IEEE International Ultrasonics Symposium, 2011