Search

In this study the dynamic behavior of a layered viscoelastic medium in response to the harmonic and impulsive acoustic radiation force applied to its surface was investigated both theoretically and experimentally. An analytical solution for a layered viscoelastic compressible medium in frequency and time domains was obtained using the Hankel transform. A special incompressible case was considered to model soft biological tissues. To verify our theoretical model, experiments were performed using tissue-like gel-based phantoms with varying mechanical properties. A 3.5 MHz single-element focused ultrasound transducer was used to apply the radiation force at the surface of the phantoms. A phase-sensitive optical coherence tomography system was used to track the displacements of the phantom surface. Theoretically predicted displacements were compared with experimental measurements. The role of the depth dependence of the elastic properties of a medium in its response to an acoustic pulse at the surface was studied. It was shown that the low-frequency vibrations at the surface are more sensitive to the deep layers than high-frequency ones. Therefore, the proposed model in combination with spectral analysis can be used to evaluate depth-dependent distribution of the mechanical properties based on the measurements of the surface deformation. [ABSTRACT FROM AUTHOR]

Treatment of deep venous thrombosis (DVT)—a primary cause of potentially fatal pulmonary embolism (PE)—depends on the age of the thrombus. The existing clinical imaging methods are capable of visualizing a thrombus but cannot determine the age of the blood clot. Therefore, there is a need for an imaging technique to reliably diagnose and adequately stage DVT. To stage DVT (i.e., to determine the age of the thrombus, and therefore, to differentiate acute from chronic DVT), we explored photoacoustic imaging, a technique capable of noninvasive measurements of the optical absorption in tissue. Indeed, optical absorption of the blood clot changes with age, since maturation of DVT is associated with significant cellular and molecular reorganization. The ultrasound and photoacoustic imaging studies were performed using DVT-mimicking phantoms and phantoms with embedded acute and chronic thrombi obtained from an animal model of DVT. The location and structure of the clots were visualized using ultrasound imaging, while the composition, and therefore age, of thrombi were related to the magnitude and spatiotemporal characteristics of the photoacoustic signal. Overall, the results of our study suggest that combined ultrasound and photoacoustic imaging of thrombi may be capable of simultaneous detection and staging of DVT. [ABSTRACT FROM AUTHOR]

An ultrasound technique to measure the spatial and temporal behavior of the laser-induced cavitation bubble is introduced. The cavitation bubbles were formed in water and in gels using a nanosecond pulsed Nd:YAG laser operating at 532 nm. A focused, single-element, 25-MHz ultrasound transducer was employed both to detect the acoustic emission generated by plasma expansion and to acoustically probe the bubble at different stages of its evolution. The arrival time of the passive acoustic emission was used to estimate the location of the cavitation bubble’s origin and the time of flight of the ultrasound pulse-echo signal was used to define its spatial extent. The results of ultrasound estimations of the bubble size were compared and found to be in agreement with both the direct optical measurements of the stationary bubble and the theoretical estimates of bubble dynamics derived from the well-known Rayleigh model of a cavity collapse. The results of this study indicate that the proposed quantitative ultrasound technique, capable of detecting and accurately measuring laser-induced cavitation bubbles in water and in a tissue-like medium, could be used in various biomedical and clinical applications. [ABSTRACT FROM AUTHOR]