Author
H. Ponnekanti
Bio: H. Ponnekanti is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Elastography & Imaging phantom. The author has an hindex of 5, co-authored 5 publications receiving 4318 citations.
Papers
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TL;DR: Initial results of several phantom and excised animal tissue experiments are reported which demonstrate the ability of this technique to quantitatively image strain and elastic modulus distributions with good resolution, sensitivity and with diminished speckle.
3,636 citations
TL;DR: A new elastography system based on a linear array transducer that is suitable for in vivo scanning is introduced and tissue mimicking phantom experiments and preliminary in vivo breast and muscle elastograms confirming the feasibility of performing elastographs in vivo are described.
434 citations
TL;DR: A literature review of a variety of methods for the estimation of tissue elasticity that have been reported in the literature in the past 15 years, and of data on the elastic properties of soft tissues.
296 citations
TL;DR: An analytical model to study the behavior of stress along the compression axis for different configurations of opposing circular compressors, as applied to elastography, based on a hypothesis that the axial stress is the superposition of the individual components of the stresses derived from the boundary conditions at either end.
Abstract: We describe an analytical model to study the behavior of stress along the compression axis for different configurations of opposing circular compressors, as applied to elastography. The method is based on a hypothesis that the axial stress at any point on the axis is the superposition of the individual components of the stresses derived from the boundary conditions at either end. The determination of the axial stress behavior according to the model permits the correction of certain elastograms for depth-dependent stress. Experimental results have been presented to corroborate the model.
72 citations
TL;DR: An experimental ultrasonic method capable of imaging the two-dimensional distribution of longitudinal stress in an elastic, tissue-like material due to an external compressor of arbitrary size or shape and boundary conditions is described.
Abstract: We describe an experimental ultrasonic method capable of imaging the two-dimensional distribution of longitudinal stress in an elastic, tissue-like material due to an external compressor of arbitrary size or shape and boundary conditions. The method involves the use of a compressor and an opposing ultrasonic transducer. Local strains are derived from the ultrasonic backscatter signals before and after compression using cross correlation analysis. The strain distribution is converted to a stress map by assuming a linear stress-strain relationship. The technique is useful for quantifying the corrections that must be made to images of the elastic modulus of tissue (elastograms) due to the effects of compressor size and shape, depth and boundary conditions. It is also useful for experimental modeling of stress distributions in elastic media.
46 citations
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TL;DR: Liver elasticity measurements were reproducible, operator-independent and well correlated and the intra- and interoperator reproducibility of the technique, as well as its ability to quantify liver fibrosis, were evaluated in 106 patients with chronic hepatitis C.
Abstract: Chronic hepatitis is accompanied by progressive deposit of hepatic fibrosis, which may lead to cirrhosis. Evaluation of liver fibrosis is, thus, of great clinical interest and, up to now, has been assessed with liver biopsy. This work aims to evaluate a new noninvasive device to quantify liver fibrosis: the shear elasticity probe or fibroscan. This device is based on one-dimensional (1-D) transient elastography, a technique that uses both ultrasound (US) (5 MHz) and low-frequency (50 Hz) elastic waves, whose propagation velocity is directly related to elasticity. The intra- and interoperator reproducibility of the technique, as well as its ability to quantify liver fibrosis, were evaluated in 106 patients with chronic hepatitis C. Liver elasticity measurements were reproducible (standardized coefficient of variation: 3%), operator-independent and well correlated (partial correlation coefficient = 0.71, p /= F2) and with cirrhosis ( = F4), respectively. The Fibroscan is a noninvasive, painless, rapid and objective method to quantify liver fibrosis.
2,517 citations
TL;DR: The first in vivo investigations made on healthy volunteers emphasize the potential clinical applicability of SSI for breast cancer detection and results validating SSI in heterogeneous phantoms are presented.
Abstract: Supersonic shear imaging (SSI) is a new ultrasound-based technique for real-time visualization of soft tissue viscoelastic properties. Using ultrasonic focused beams, it is possible to remotely generate mechanical vibration sources radiating low-frequency, shear waves inside tissues. Relying on this concept, SSI proposes to create such a source and make it move at a supersonic speed. In analogy with the "sonic boom" created by a supersonic aircraft, the resulting shear waves will interfere constructively along a Mach cone, creating two intense plane shear waves. These waves propagate through the medium and are progressively distorted by tissue heterogeneities. An ultrafast scanner prototype is able to both generate this supersonic source and image (5000 frames/s) the propagation of the resulting shear waves. Using inversion algorithms, the shear elasticity of medium can be mapped quantitatively from this propagation movie. The SSI enables tissue elasticity mapping in less than 20 ms, even in strongly viscous medium like breast. Modalities such as shear compounding are implementable by tilting shear waves in different directions and improving the elasticity estimation. Results validating SSI in heterogeneous phantoms are presented. The first in vivo investigations made on healthy volunteers emphasize the potential clinical applicability of SSI for breast cancer detection.
2,300 citations
TL;DR: The results indicate that displacement patterns corresponding to cyclic displacements smaller than 200 nanometers can be measured and suggest the feasibility of a medical imaging technique for delineating elasticity and other mechanical properties of tissue.
Abstract: A nuclear magnetic resonance imaging (MRI) method is presented for quantitatively mapping the physical response of a material to harmonic mechanical excitation. The resulting images allow calculation of regional mechanical properties. Measurements of shear modulus obtained with the MRI technique in gel materials correlate with independent measurements of static shear modulus. The results indicate that displacement patterns corresponding to cyclic displacements smaller than 200 nanometers can be measured. The findings suggest the feasibility of a medical imaging technique for delineating elasticity and other mechanical properties of tissue.
2,015 citations
TL;DR: To evaluate the dynamic range of tissue imaged by elastography, the mechanical behavior of breast and prostate tissue samples subject to compression loading has been investigated and the data show that breast fat tissue has a constant modulus over the strain range tested while the other tissues have a modulus that is dependent on the strain level.
1,698 citations
TL;DR: A physical and mathematical basis of SWEI is presented and some experimental results of pilot studies proving feasibility of this new ultrasonic technology are presented, including a theoretical model of shear oscillations in soft biological tissue remotely induced by the radiation force of focused ultrasound.
Abstract: Shear wave elasticity imaging (SWEI) is a new approach to imaging and characterizing tissue structures based on the use of shear acoustic waves remotely induced by the radiation force of a focused ultrasonic beam. SWEI provides the physician with a virtual "finger" to probe the elasticity of the internal regions of the body. In SWEI, compared to other approaches in elasticity imaging, the induced strain in the tissue can be highly localized, because the remotely induced shear waves are attenuated fully within a very limited area of tissue in the vicinity of the focal point of a focused ultrasound beam. SWEI may add a new quality to conventional ultrasonic imaging or magnetic resonance imaging. Adding shear elasticity data ("palpation information") by superimposing color-coded elasticity data over ultrasonic or magnetic resonance images may enable better differentiation of tissues and further enhance diagnosis. This article presents a physical and mathematical basis of SWEI with some experimental results of pilot studies proving feasibility of this new ultrasonic technology. A theoretical model of shear oscillations in soft biological tissue remotely induced by the radiation force of focused ultrasound is described. Experimental studies based on optical and magnetic resonance imaging detection of these shear waves are presented. Recorded spatial and temporal profiles of propagating shear waves fully confirm the results of mathematical modeling. Finally, the safety of the SWEI method is discussed, and it is shown that typical ultrasonic exposure of SWEI is significantly below the threshold of damaging effects of focused ultrasound.
1,632 citations