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Ultrasound in medicine & biology  2014;40(8):1785-1795.
Our aims were (i) to compare in vivo measurements of myocardial elasticity by shear wave dispersion ultrasound vibrometry (SDUV) with those by the conventional pressure-segment length method, and (ii) to quantify changes in myocardial viscoelasticity during systole and diastole after reperfused acute myocardial infarction. The shear elastic modulus (μ1) and viscous coefficient (μ2) of left ventricular myocardium were measured by SDUV in 10 pigs. Young’s elastic modulus was independently measured by the pressure-segment length method. Measurements made with the SDUV and pressure-segment length methods were strongly correlated. At reperfusion, μ1 and μ2 in end-diastole were increased. Less consistent changes were found during systole. In all animals, μ1 increased linearly with left ventricular pressure developed during systole. Preliminary results suggest that m1 is preload dependent. This is the first study to validate in vivo measurements of myocardial elasticity by a shear wave method. In this animal model, the alterations in myocardial viscoelasticity after a myocardial infarction were most consistently detected during diastole.
PMCID: PMC4118646  PMID: 24814645
Echocardiography; Elasticity; Elastography; Myocardial stiffness; Myocardial infarction; Shear elasticity; Shear wave; Ultrasound; Viscoelasticity
2.  Improved Shear Wave Motion Detection Using Pulse-Inversion Harmonic Imaging with a Phased Array Transducer 
IEEE transactions on medical imaging  2013;10.1109/TMI.2013.2280903.
Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the shear wave motion and give consistent shear wave speed measurements while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index (BMI) higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve shear wave motion tracking and thus potentially facilitate more robust assessment of tissue elasticity by SWE.
PMCID: PMC3947393  PMID: 24021638
Harmonic imaging; shear wave elastography; acoustic radiation force; pulse inversion; in vivo human heart; transthoracic scanning; diastolic left ventricle stiffness
3.  Measurement of viscoelastic properties of in vivo swine myocardium using Lamb Wave Dispersion Ultrasound Vibrometry (LDUV) 
Viscoelastic properties of the myocardium are important for normal cardiac function and may be altered by disease. Thus, quantification of these properties may aid with evaluation of the health of the heart. Lamb Wave Dispersion Ultrasound Vibrometry (LDUV) is a shear wave-based method that uses wave velocity dispersion to measure the underlying viscoelastic material properties of soft tissue with plate-like geometries. We tested this method in eight pigs in an open-chest preparation. A mechanical actuator was used to create harmonic, propagating mechanical waves in the myocardial wall. The motion was tracked using a high frame rate acquisition sequence, typically 2500 Hz. The velocities of wave propagation were measured over the 50–400 Hz frequency range in 50 Hz increments. Data were acquired over several cardiac cycles. Dispersion curves were fit with a viscoelastic, anti-symmetric Lamb wave model to obtain estimates of the shear elasticity, μ1, and viscosity, μ2 as defined by the Kelvin-Voigt rheological model. The sensitivity of the Lamb wave model was also studied using simulated data. We demonstrated that wave velocity measurements and Lamb wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle.
PMCID: PMC3562367  PMID: 23060325
4.  Vibroacoustography for the assessment of total hip arthroplasty 
Clinics  2013;68(4):463-468.
This paper proposes imaging with 3-dimensional vibroacoustography for postoperatively assessing the uncovered cup area after total hip arthroplasty as a quantitative criterion to evaluate implant fixation.
A phantom with a bone-like structure covered by a tissue-mimicking material was used to simulate a total hip arthroplasty case. Vibroacoustography images of the uncovered cup region were generated using a two-element confocal ultrasound transducer and a hydrophone inside a water tank. Topological correction based on the geometry of the implant was performed to generate a 3-dimensional representation of the vibroacoustography image and to accurately evaluate the surface. The 3-dimensional area obtained by the vibroacoustography approach was compared to the area evaluated by a 3-dimensional motion capture system.
The vibroacoustography technique provided high-resolution, high-contrast, and speckle-free images with less sensitivity to the beam incidence. Using a 3-dimensional-topology correction of the image, we accurately estimated the uncovered area of the implant with a relative error of 8.1% in comparison with the motion capture system measurements.
Measurement of the cup coverage after total hip arthroplasty has not been well established; however, the covered surface area of the acetabular component is one of the most important prognostic factors. The preliminary results of this study show that vibroacoustography is a 3-dimensional approach that can be used to postoperatively evaluate total hip arthroplasty. The favorable results also provide an impetus for exploring vibroacoustography in other bone or implant surface imaging applications.
PMCID: PMC3634963  PMID: 23778334
Arthroplasty; 3D Imaging; Vibroacoustography
5.  In vivo thyroid vibro-acoustography: a pilot study 
BMC Medical Imaging  2013;13:12.
The purpose of this study was to evaluate the utility of a noninvasive ultrasound-based method, vibro-acoustography (VA), for thyroid imaging and determine the feasibility and challenges of VA in detecting nodules in thyroid.
Our study included two parts. First, in an in vitro study, experiments were conducted on a number of excised thyroid specimens randomly taken from autopsy. Three types of images were acquired from most of the specimens: X-ray, B-mode ultrasound, and vibro-acoustography. The second and main part of the study includes results from performing VA and B-mode ultrasound imaging on 24 human subjects with thyroid nodules. The results were evaluated and compared qualitatively.
In vitro vibro-acoustography images displayed soft tissue structures, microcalcifications, cysts and nodules with high contrast and no speckle. In this group, all of US proven nodules and all of X-ray proven calcifications of thyroid tissues were detected by VA. In vivo results showed 100% of US proven calcifications and 91% of the US detected nodules were identified by VA, however, some artifacts were present in some cases.
In vitro and in vivo VA images show promising results for delineating the detailed structure of the thyroid, finding nodules and in particular calcifications with greater clarity compare to US. Our findings suggest that, with further development, VA may be a suitable imaging modality for clinical thyroid imaging.
PMCID: PMC3618245  PMID: 23530993
Elasticity imaging techniques; Vibro-acoustography; Thyroid neoplasm; Thyroid nodule; Ultrasound; Imaging
6.  Bias Observed in Time-of-flight Shear Wave Speed Measurements Using Radiation Force of a Focused Ultrasound Beam 
Ultrasound in medicine & biology  2011;37(11):1884-1892.
Measurement of shear wave propagation speed has important clinical applications because it is related to tissue stiffness and health state. Shear waves can be generated in tissues by the radiation force of a focused ultrasound beam (push beam). Shear wave speed can be measured by tracking its propagation laterally from the push beam focus using the time-of-flight principle. This study shows that shear wave speed measurements with such methods can be transducer, depth, and lateral tracking range dependent. Three homogeneous phantoms with different stiffness were studied using curvilinear and linear array transducer. Shear wave speed measurements were made at different depths, using different aperture sizes for push, and at different lateral distance ranges from the push beam. The curvilinear transducer shows a relatively large measurement bias that is depth dependent. The possible causes of the bias and options for correction are discussed. These bias errors must be taken into account to provide accurate and precise time-of-flight shear wave speed measurements for clinical use.
PMCID: PMC3199321  PMID: 21924817
Shear wave speed; Liver fibrosis; Bias; ARFI
7.  Breast vibro-acoustography: initial results show promise 
Breast Cancer Research : BCR  2012;14(5):R128.
Vibro-acoustography (VA) is a recently developed imaging modality that is sensitive to the dynamic characteristics of tissue. It detects low-frequency harmonic vibrations in tissue that are induced by the radiation force of ultrasound. Here, we have investigated applications of VA for in vivo breast imaging.
A recently developed combined mammography-VA system for in vivo breast imaging was tested on female volunteers, aged 25 years or older, with suspected breast lesions on their clinical examination. After mammography, a set of VA scans was acquired by the experimental device. In a masked assessment, VA images were evaluated independently by 3 reviewers who identified mass lesions and calcifications. The diagnostic accuracy of this imaging method was determined by comparing the reviewers' responses with clinical data.
We collected images from 57 participants: 7 were used for training and 48 for evaluation of diagnostic accuracy (images from 2 participants were excluded because of unexpected imaging artifacts). In total, 16 malignant and 32 benign lesions were examined. Specificity for diagnostic accuracy was 94% or higher for all 3 reviewers, but sensitivity varied (69% to 100%). All reviewers were able to detect 97% of masses, but sensitivity for detection of calcification was lower (≤ 72% for all reviewers).
VA can be used to detect various breast abnormalities, including calcifications and benign and malignant masses, with relatively high specificity. VA technology may lead to a new clinical tool for breast imaging applications.
PMCID: PMC4053105  PMID: 23021305
acoustic imaging; breast lesions; radiation force breast imaging; ultrasound; vibro-acoustography
8.  Implementation of Vibro-acoustography on a Clinical Ultrasound System 
Vibro-acoustography is an ultrasound-based imaging modality that uses two ultrasound beams of slightly different frequencies to produce images based on the acoustic response due to harmonic ultrasound radiation force excitation at the difference frequency between the two ultrasound frequencies. Vibro-acoustography has demonstrated feasibility and usefulness in imaging of breast and prostate tissue. However, previous studies have been performed either in controlled water tank settings or a prototype breast scanner equipped with a water tank. In order to make vibro-acoustography more accessible and relevant to clinical use, we report here on the implementation of vibro-acoustography on a General Electric Vivid 7 ultrasound scanner. In this paper, we will describe software and hardware modifications that were performed to make vibro-acoustography functional on this system. We will discuss aperture definition for the two ultrasound beams and beamforming using a linear array transducer. Experimental results from beam measurements and phantom imaging studies will be shown. The implementation of vibro-acoustography provides a step towards clinical translation of this imaging modality for applications in various organs including breast, prostate, thyroid, kidney, and liver.
PMCID: PMC3138131  PMID: 21693399
9.  Air-coupled ultrasound stimulated optical vibrometry for resonance analysis of rubber tubes 
Ultrasonics  2008;49(1):26-30.
Air-coupled ultrasound stimulated optical vibrometry is proposed to generate and detect the resonances of a rubber tube in air. Amplitude-modulated (AM) focused ultrasound radiation force from a broadband air-coupled ultrasound transducer with center frequency of 500 kHz is used to generate a low frequency vibration in the tube. The resonances of several modes of the tube are measured with a laser vibrometer of 633 nm wavelength. A wave propagation approach is used to calculate the resonances of the tube from its known material properties. Theoretical and experimental resonance frequencies agree within 5%. This method may be useful in measuring the in vitro elastic properties of arteries from the resonance measurements in air. It may also be helpful in better understanding the coupling effects of surrounding tissue and interior blood on the vessel wall by measuring the resonance of the vessel in vitro and in vivo.
PMCID: PMC2614219  PMID: 18499208
Noncontact; resonance; tube; air-coupled ultrasound; vibrometry
10.  In Vivo Vibroacoustography of Large Peripheral Arteries 
Investigative radiology  2008;43(4):243-252.
Vibroacoustography allows imaging of objects on the basis of their acoustic signal emitted during low-frequency (kHz) vibrations produced by 2 intersecting ultrasound beams at slightly different frequencies. This study tested the feasibility of using vibroacoustography to distinguish between normal and calcified femoral arteries in a pig model.
Materials and Methods
Thirteen normal porcine femoral arteries, 7 with experimentally induced arterial calcifications, and 1 control artery injected with saline only were scanned in vivo. Images were obtained at 45 kHz using a 3 MHz confocal transducer. The acoustic emission signal was detected with a hydrophone placed on the animal’s limb. Images were reconstructed on the basis of the amplitude of the acoustic emission signal. Vessel patency, vessel dimensions, and the extent of calcified plaques were confirmed in vivo by angiography and conventional ultrasound. Excised arteries were reexamined with vibroacoustography, X-ray radiography, and histology.
In vivo, vibroacoustography produced high-resolution, speckle-free images with a high level of anatomic detail. Measurements of femoral artery diameter were similar by vibroacoustography and conventional ultrasound (mean difference ± SD, 0.1 ± 0.4 mm). Calcified plaque area measured by different methods was comparable (vibroacoustography, in vivo: 1.0 ± 0.9 cm2; vibroacoustography in vitro: 1.1 ± 0.6 cm2; X-ray radiography: 0.9 ± 0.6 cm2). The reproducibility of measurements was high. Sensitivity and specificity for detecting calcifications were 100% and 86%, respectively, and positive and negative predictive values were 77% and 100%, respectively.
Vibroacoustography provides accurate and reproducible measurements of femoral arteries and vascular calcifications in living animals.
PMCID: PMC2535937  PMID: 18340248
arterial calcifications; arterial stiffness; atherosclerosis; ultrasound; vibroacoustography

Results 1-10 (10)