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Desai R.R.,Texas A&M University | Krouskop T.A.,National Center for Human Performance | Righetti R.,Texas A&M University
Ultrasonic Imaging | Year: 2010

Tissue Harmonic Imaging (THI) is a relatively new modality that has had a significant impact in the ultrasound field. In the recent past, imaging the mechanical properties of tissues using elastography has also gained great interest. In this paper, we investigate the feasibility of combining these two state-of-the-art ultrasound-imaging modalities. The performance of elastograms obtained using harmonic ultrasonic signals is studied with simulations and compared to the performance of conventional elastograms using standard statistical methods. Experiments are used as a proof of the technical feasibility of generating tissue-harmonic elastograms using experimental harmonic signals. The results of our simulation study indicate that all image quality factors considered in this study (elastographic signal-to-noise ratio, elastographic contrast-to-noise ratio and spatial resolution) may be improved when using harmonic ultrasonic signals, provided that the ultrasound system is characterized by high bandwidth, high sampling frequency and large lateral sampling. Preliminary experimental results suggest that it is technically feasible to generate experimental elastograms using harmonic signals, provided that the sonographic signal-to-noise ratio of the pre- and postcompression harmonic frames is suffi ciently high to guarantee reliable values of correlation. Copyright 2010 by Dynamedia, Inc. Source


Nair S.P.,Texas A&M University | Yang X.,Texas A&M University | Krouskop T.A.,National Center for Human Performance | Righetti R.,Texas A&M University
IEEE Transactions on Medical Imaging | Year: 2011

New elastographic techniques such as poroelastography and viscoelasticity imaging aim at imaging the temporal mechanical behavior of tissues. These techniques usually involve the use of curve fitting methods being applied to noisy data to estimate new elastographic parameters. As of today, however, current elastographic implementations of poroelastography and viscoelasticity imaging methods are in general too slow and not optimized for clinical applications. Furthermore, image quality performance of these new elastographic techniques is still largely unknown due to a paucity of data and the lack of systematic studies that analyze their performance limitations. In this paper, we propose a new elastographic time constant (TC) estimator, which is based on the use of the least square error (LSE) curve-fitting method and the LevenbergMarquardt (LM) optimization rule as applied to noisy elastographic data obtained from a material in a creep-type experiment. The algorithm is executed on a massively parallel general purpose graphics processing unit (GPGPU) to achieve real-time performance. The estimator's performance is analyzed using simulations. Experimental results obtained from poroelastic phantoms are presented as a proof of principle of the new estimator's technical applicability on real experimental data. The results of this study demonstrate that the newly proposed elastographic estimator can produce highly accurate and sensitive elastographic TC estimates in real-time and at high signal-to-noise ratios. © 2010 IEEE. Source


Chaudhry A.,Texas A&M University | Unnikrishnan G.,Texas A&M University | Reddy J.N.,Texas A&M University | Krouskop T.A.,National Center for Human Performance | Righetti R.,Texas A&M University
IEEE Transactions on Medical Imaging | Year: 2013

Elastography is a well-established imaging modality. While a number of studies aimed at evaluating the performance of elastographic techniques are retrievable in the literature, very little information is available on the effects that the presence of an underlying permeability contrast in the tissue may have on the resulting elastograms. Permeability is a fundamental tissue parameter, which characterizes the ease with which fluid can move within a tissue. This parameter plays a central role both biomechanically in the description of the temporal behavior of fluid-filled tissues and clinically in the development of a number of diagnostic and therapeutic modalities. In this paper, we present a simulation study that investigates selected elastographic image quality factors in nonhomogeneous materials, modeled as poroelastic media with different geometries and permeability contrasts. The results of this study indicate that the presence of an underlying permeability contrast may create a new contrast mechanism in the spatial and temporal distributions of the axial strains and the effective Poisson's ratios experienced by the tissue and as imaged by the corresponding elastograms. The effect of permeability on the elastographic image quality factors analyzed in this study was found to be a nonsymmetric function of the underlying mechanical contrast between background and target, the geometry of the material and the boundary conditions. © 2012 IEEE. Source


Layne C.S.,University of Houston | Layne C.S.,Center for Neuromotor and Biomechanics Research | Layne C.S.,National Center for Human Performance | Chelette A.M.,University of Houston | And 5 more authors.
Somatosensory and Motor Research | Year: 2015

It has been proposed that proprioceptive input is essential to the development of a locomotor body schema that is used to guide the assembly of successful walking. Proprioceptive information is used to signal the need for, and promotion of, locomotor adaptation in response to environmental or internal modifications. The purpose of this investigation was to determine if tendon vibration applied to either the hamstrings or quadriceps of participants experiencing split-belt treadmill walking modified lower limb kinematics during the early adaptation period. Modifications in the adaptive process in response to vibration would suggest that the sensory-motor system had been unsuccessful in down weighting the disruptive proprioceptive input resulting from vibration. Ten participants experienced split-belt walking, with and without vibration, while gait kinematics were obtained with a 12-camera collection system. Bilateral hip, knee, and ankle joint angles were calculated and the first five strides after the split were averaged for each subject to create joint angle waveforms for each of the assessed joints, for each experimental condition. The intralimb variables of stride length, percent stance time, and relative timing between various combinations of peak joint angles were assessed using repeated measures MANOVA. Results indicate that vibration had very little impact on the split-belt walking adaptive process, although quadriceps vibration did significantly reduce percent stance time by 1.78% relative to the no vibration condition. The data suggest that the perceptual-motor system was able to down weight the disrupted proprioceptive input such that the locomotor body schema was able to effectively manage the lower limb patterns of motion necessary to adapt to the changing belt speed. Complementary explanations for the current findings are also discussed. © 2015 Informa UK Ltd. All rights reserved. Source

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