Armen Sarvazyan

Method and device for shear wave elasticity imaging

A method and devices for Shear Wave Elasticity Imaging (SWEI). The method employs a focused ultrasound transducer which remotely induces a shear wave in a tissue by sending modulated ultrasonic pulses. The shear wave of the frequency of the modulating signal is detected. The values of the shear modulus and dynamic shear viscosity of tissue are evaluated from the measured values of velocity and attenuation of shear waves. Several devices for carrying out the method are described. Devices based on the method can be used as a diagnostic tool in the detection of abnormalities in tissue, such as those caused by cancer or other lesions and characterizing processes in tissues accompanied by changes in their mechanical properties.

Acoustic radiation force and streaming induced by focused nonlinear ultrasound in a dissipative medium

Based on asymptotic methods recently developed in nonlinear acoustics, analytical solutions of the equations for the radiation force induced by nonlinear focused ultrasound in a dissipative medium are considered. Equations describing spatial structure of the radiation force field in the paraxial region of the ultrasound beam and the spatial–temporal behavior of the induced nonlinear streaming are derived. The equations enable analytical investigation of dependencies of radiation pressure and resulting streaming on the acoustic field and medium parameters. Estimates have shown that nonlinearity of medium can significantly enhance radiation force in the focal region at the intensities lower than those used in ultrasound devices for medical imaging. The initiation of acoustical streaming by radiation force is considered, and the spatial and temporal characteristics of induced flow are discussed. Both acoustic and hydrodynamic nonlinearities are taken into account. The paper concludes by discussing possible m...

Mechanical Imaging of the Breast

In this paper, we analyze the physical basis for elasticity imaging of the breast by measuring breast skin stress patterns that result from a force sensor array pressed against the breast tissue. Temporal and spatial changes in the stress pattern allow detection of internal structures with different elastic properties and assessment of geometrical and mechanical parameters of these structures. The method entitled mechanical imaging is implemented in the breast mechanical imager (BMI), a compact device consisting of a hand held probe equipped with a pressure sensor array, a compact electronic unit, and a touchscreen laptop computer. Data acquired by the BMI allows calculation of size, shape, consistency/hardness, and mobility of detected lesions. The BMI prototype has been validated in laboratory experiments on tissue models and in an ongoing clinical study. The obtained results prove that the BMI has potential to become a screening and diagnostic tool that could largely supplant clinical breast examination through its higher sensitivity, quantitative record storage, ease-of-use, and inherent low cost.

Influence of Drug Binding on DNA Hydration: Acoustic and Densimetric Characterizations of Netropsin Binding to the Poly(dAdT).cntdot.Poly(dAdT) and Poly(dA).cntdot.Poly(dT) Duplexes and the Poly(dT).cntdot.Poly(dA).cntdot.Poly(dT) Triplex at 25 .degree.C

We use high-precision acoustic and densimetric techniques to determine, at 25 degrees C, the changes in volume, delta V, and adiabatic compressibility, delta Ks, that accompany the binding of netropsin to the poly(dAdT).poly(dAdT) and poly(dA).poly(dT) duplexes, as well as to the poly(dT).poly(dA).poly(dT) triplex. We find that netropsin binding to the heteropolymeric poly(dAdT).poly(dAdT) duplex is accompanied by negative changes in volume, delta V, and small positive changes in compressibility, delta Ks. By contrast, netropsin binding to the homopolymeric poly(dA).poly(dT) duplex is accompanied by large positive changes in both volume, delta V, and compressibility, delta Ks. Furthermore, netropsin binding to the poly(dT).poly(dA).poly(dT) triplex causes changes in both volume and compressibility that are nearly twice as large as those observed when netropsin binds to the poly(dA).poly(dT) duplex. We interpret these macroscopic data in terms of binding-induced microscopic changes in the hydration of the DNA structures and the drug. Specifically, we find that netropsin binding induces the release of approximately 22 waters from the hydration shell of the poly(dAdT).poly(dAdT) heteropolymeric duplex, approximately 40 waters from the hydration shell of the poly(dA).poly(dT) homopolymeric duplex, and about 53 waters from the hydration shell of the poly(dA).poly(dT), induces the release of 18 more water molecules than netropsin binding to the heteropolymeric duplex, poly(dAdT).poly(dAdT). On the basis of apparent molar volume, phi V, and apparent molar adiabatic compressibility, phi Ks, values for the initial drug-free and final drug-bound states of the two all-AT duplexes, we propose that the larger dehydration of the poly(dA).poly(dT) duplex reflects, in part, the formation of a less hydrated poly(dA).poly(dT)-netropsin complex compared with the corresponding poly(dAdT).poly(dAdT)-netropsin complex. In conjunction with our previously published entropy data [Marky, L. A., & Breslauer, K. J. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 4359-4363], we calculate that each water of hydration released to the bulk solvent by ligand binding contributes 1.6 cal K-1 mol-1 to the entropy of binding. This value corresponds to the average difference between the partial molar entropy of water in the bulk state and water in the hydration shells of the two all-AT duplexes. When netropsin binds to the poly(dT).poly(dA).poly(dT) triplex, the changes in both volume and compressibility suggest that the binding event induces more dehydration of the triplex than of the duplex state. Specifically, we calculate that netropsin binding to the poly(dT).poly(dA).poly(dT) triplex causes the release of 13 more waters than netropsin binding to the poly(dA).poly(dT) duplex.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic waves in medical imaging and diagnostics.

Up until about two decades ago acoustic imaging and ultrasound imaging were synonymous. The term ultrasonography, or its abbreviated version sonography, meant an imaging modality based on the use of ultrasonic compressional bulk waves. Beginning in the 1990s, there started to emerge numerous acoustic imaging modalities based on the use of a different mode of acoustic wave: shear waves. Imaging with these waves was shown to provide very useful and very different information about the biological tissue being examined. We discuss the physical basis for the differences between these two basic modes of acoustic waves used in medical imaging and analyze the advantages associated with shear acoustic imaging. A comprehensive analysis of the range of acoustic wavelengths, velocities and frequencies that have been used in different imaging applications is presented. We discuss the potential for future shear wave imaging applications.

Prostate mechanical imaging: 3-D image composition and feature calculations

We have developed a method and a device entitled prostate mechanical imager (PMI) for the real-time imaging of prostate using a transrectal probe equipped with a pressure sensor array and position tracking sensor. PMI operation is based on measurement of the stress pattern on the rectal wall when the probe is pressed against the prostate. Temporal and spatial changes in the stress pattern provide information on the elastic structure of the gland and allow two-dimensional (2-D) and three-dimensional (3-D) reconstruction of prostate anatomy and assessment of prostate mechanical properties. The data acquired allow the calculation of prostate features such as size, shape, nodularity, consistency/hardness, and mobility. The PMI prototype has been validated in laboratory experiments on prostate phantoms and in a clinical study. The results obtained on model systems and in vivo images from patients prove that PMI has potential to become a diagnostic tool that could largely supplant DRE through its higher sensitivity, quantitative record storage, ease-of-use and inherent low cost

Doppler ultrasound detection of shear waves remotely induced in tissue phantoms and tissue in vitro

In shear wave elasticity imaging (SWEI), mechanical excitation within the tissue is remotely generated using radiation force of focused ultrasound. The induced shear strain is subsequently detected to estimate visco-elastic properties of tissue and thus aid diagnostics. In this paper, the mechanical response of tissue to radiation force was detected using a modified ultrasound Doppler technique. The experiments were performed on tissue mimicking and tissue containing phantoms using a commercial diagnostic scanner. This scanner was modified to control both the pushing and probing beams. The pushing beam was fired repetitively along a single direction while interlaced probing beams swept the surrounding region of interest to detect the induced motion. The detectability of inhomogeneous inclusions using ultrasonic Doppler SWEI method has been demonstrated in this study. The displacement fields measured in elastic phantoms clearly reveal the oscillatory nature of the mechanical relaxation processes in response to impulsive load due to the boundary effects. This relaxation dynamics was also present in cooked muscle tissue, but was not detected in more viscous and less elastic phantom and raw muscles. Presence of a local heterogeneity in the vicinity of the focal region of the pushing beam results in generation of a standing wave field pattern which is manifested in the oscillatory response of the excited region of the tissue. There has been made an assumption that dynamic characteristics of the relaxation process may be used for visualization of inhomogeneities.

Vaginal Tactile Imaging

Changes in the elasticity of the vaginal walls, connective support tissues, and muscles are thought to be significant factors in the development of pelvic organ prolapse, a highly prevalent condition affecting at least 50% of women in the United States during their lifetimes. It creates two predominant concerns specific to the biomechanical properties of pelvic support tissues: how does tissue elasticity affect the development of pelvic organ prolapse and how can functional elasticity be maintained through reconstructive surgery. We designed a prototype of vaginal tactile imager (VTI) for visualization and assessment of elastic properties of pelvic floor tissues. In this paper, we analyze applicability of tactile imaging for evaluation of reconstructive surgery results and characterization of normal and pelvic organ prolapse conditions. A pilot clinical study with 13 patients demonstrated that VTI allows imaging of vaginal walls with increased rigidity due to implanted mesh grafts following reconstructive pelvic surgery and VTI has the potential for prolapse characterization and detection.

Application of the dual-frequency ultrasonometer for osteoporosis detection

The paper presents results of a clinical validation study of Bone UltraSonic Scanner (BUSS), a novel dual-frequency axial transmission ultrasonometer, developed by Artann Laboratories. Assessment of bone conditions is based on evaluating relative changes of the axial profiles of ultrasonic characteristics in long bones and utilizes bulk and guided acoustic waves. The objective of this study was to determine the ability of BUSS to discriminate osteoporosis development stages. A total of 93 menopausal and post-menopausal women divided into five groups from normal to advanced osteoporosis according to their DXA hip t-score were enrolled in the study. The 2D waveform profiles at low (0.1 MHz) and high (1 MHz) frequencies were obtained by scanning 15 cm along the proximal tibia. A multi-parametric linear classifier based on a set of the parameters derived from 2D acoustic waveform profiles has been developed. The efficiency of this classifier in differentiating osteoporosis from a normal sample was assessed using a receiver operating characteristic (ROC) curve analysis. Based on the ROC analysis, BUSS demonstrated 76% sensitivity and 70% specificity to DXA-identified osteoporosis. The area under the ROC curve, which is a measure of how well a parameter can distinguish between the two diagnostic groups (diseased/normal) was 79.3%. The study confirmed BUSSs capability to discriminate between stages of bone atrophy and in particular to distinguish early changes induced by osteoporosis.

Prostate mechanical imaging: a new method for prostate assessment.

OBJECTIVES To evaluate the ability of prostate mechanical imaging (PMI) technology to provide an objective and reproducible image and to assess the prostate nodularity. METHODS We evaluated the PMI device developed by Artann Laboratories in a pilot clinical study. For the 168 patients (ages 44 to 94) who presented to an urologist for prostate evaluation, PMI-produced images and assessment of prostate size, shape, consistency/hardness, mobility, and nodularity were compared with digital rectal examination (DRE) findings. The PMI and DRE results were further tested for correlation against a transrectal ultrasound of the prostate (TRUS) guided biopsy for a subgroup of 21 patients with an elevated prostate-specific antigen level. RESULTS In 84% of the cases, the PMI device was able to reconstruct three-dimensional (3D) and 2D cross-sectional images of the prostate. The PMI System and DRE pretests were able to determine malignant nodules in 10 and 6 patients, respectively, of the 13 patients with biopsy-confirmed malignant inclusions. The PMI System findings were consistent with all 8 biopsy negative cases, whereas the DRE had 1 abnormal reading for this group. The correlation between PMI and DRE detection of palpable nodularity was 81%, as indicated by the area under the receiver operating characteristic curve. Estimates of the prostate size provided by PMI and DRE were statistically significantly correlated. CONCLUSIONS The PMI has the potential to enable a physician to obtain, examine, and store a 3D image of the prostate based on mechanical and geometrical characteristics of the gland and its internal structures.