Biomedical Acoustics Research Articles

Nonlinear dynamics of gas bubbles in viscoelastic media

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. The Keller–Miksis equation for nonlinear bubble dynamics is combined with the Voigt model for viscoelastic media. Using experimentally determined values, the effects of elasticity on bubble oscillations are studied. Inertial cavitation thresholds are determined using Rmax/R0=2, and subharmonic emissions are also estimated. The elasticity increases the threshold pressure for inertial cavitation, and subharmonic signals are significant only in a certain region of radii and driving pressures at a given frequency. These results should prove useful in cavitation detection and bubble-enhanced imaging work.

Nonlinear dynamics of gas bubbles in soft tissue

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. The previous studies are largely limited by availability of experimental data on soft tissue. To approach this problem, we combine the Keller-Miksis equation for nonlinear bubble dynamics with the linear Voigt model for viscoelastic media. Using experimentally determined values of viscoelastic properties of soft tissue as a guide, the effects of elasticity on bubble oscillations are studied. The inertial cavitation thresholds are determined using a criterion of Rmax/R0=2, and subharmonic emissions from an oscillating bubble are calculated. The results show that the presence of the elasticity increases the threshold pressure for inertial cavitation, and subharmonic signals only can be detected in a certain region of radii and driving pressures at a given frequency. These results should be useful in cavitation detection and bubble-enhanced imaging work. The model also could be used to determine values for the viscoelastic properties of soft tissue.

Application of nonlinear acoustics in the atmosphere and biomedicine

David Blackstock has made important contributions to understanding nonlinear processes in underwater acoustics, atmospheric acoustics, and biomedical acoustics. In this talk, two of these areas that David has been involved with are addressed by contrasting the evolution of sonic booms in an inhomogeneous atmosphere with the evolution of shock waves in lithotripsy (breaking of kidney stones by shock waves). The distortion of N waves generated by supersonic aircraft is affected by geometrical spreading and changes in the acoustic properties of the medium with altitude. In shock wave lithotripsy, the distortion of triangle waves is affected by geometrical spreading and changes in the acoustic properties due to layering of tissue types. In addition, the turbulent boundary layer near the ground and the inhomogeneous nature of tissue, means that both sonic booms and lithotripter shock waves pass through a random media. Calculations are presented using weak shock to compare the distortion that occurs in the two scenarios. Measurements of saturationlike effects are shown for a clinical shock wave therapy device. Numerical simulations for propagation through random media demonstrate the localized focusing and defocusing that can occur for both sonic booms and lithotripter shock waves. [Work supported in part by NIH and NASA.]

Acoustics education in Ukraine

Acoustics education in Ukraine is considered. In more than 40 universities, students learn acoustics: in the acoustics department of the National Technical University in Ukraine (only one department in Ukraine) and many related departments such as Nondestructive Testing, Physics, Electrical Engineering, etc. Acoustical specializations of departments are presented. The most promising and developing acoustical specialization is biomedical acoustics.

New initiatives in noise control reflecting on lessons from Arden House

In June 1972, the Acoustical Society held a conference on Acoustics and Societal Problems (CASP) at Arden House in Harriman, New York. Over 50 members participated in the 3-day conference, organized in seven task teams under the able general chairmanship of John C. Johnson. The 89-page report of this conference contains detailed assessments of needs and recommended actions in five scientific and technical areas of societal concern and two other areas related to communication of information and ideas. These seven areas were: (1) noise and man; (2) outdoor sound propagation and sources; (3) motor vehicle noise; (4) biomedical acoustics; (5) acoustic applications; (6) interorganizational activities and relationships; and (7) diffusion of knowledge. This paper draws upon the 20-yr-old repository of knowledge to find needs and ideas in the area of noise control that are as relevant today as they were 20 yr ago. The items found in this unfinished agenda provide a partial basis for the development of new initiatives for noise control and insight into the difficulties of their implementation. Hopefully, these ideas and insights can lead to effective execution of new initiatives in the future.

Mixture composition determination from measurements of the acoustic nonlinearity parameter

An important inverse problem in biomedical acoustics is the determination of the composition of a tissue based upon measurements of its acoustic properties. Under many circumstances, the tissue can be modeled as an ideal mixture of components, each with known or assumed properties. The measured properties of the mixture as a whole are then related to those of the components through a set of mixture laws. Once formulated, the problem can be inverted to yield the volume or mass fractions of the components present in the tissue. In this laboratory, the use of the acoustic nonlinearity parameter B/A to help infer the composition of mixtures of bioligical materials has been studied. Various mixture models have been investigated, and a modified version of Apfel's model [J. Acoust. Soc. Am. 79, 148–152 (1986)] has yielded the most useful results. This modified mixture model will be presented, along with precise data that have been obtained on biological mixtures using a novel acoustic interferometry technique reported earlier [J. Acoust. Soc. Am. Suppl. 1 80, S4 (1986)]. [Work supported by the U. S. National Institutes of Health through Grant R004GM300 19].

Use of focused ultrasonic receivers for remote measurements in biological tissues.

The feasibility of using a focusing ultrasonic transducer as a sound pressure receiver is discussed. It is shown theoretically that, at certain angular apertures of the receiver, its output signal is proportional to the sound pressure in the field point coincident with the receiver center of curvature. The receivers of this type have been demonstrated suitable for remote measurements of field spatial distribution of plane and focused ultrasonic radiators. Data are presented on the experimental testing of focused receivers in measuring acoustic fields in water, air, and certain samples of biological tissues. The instruments are sufficiently universal and allow the measurement not only of acoustic fields, but also of temperature increments in locally heated media, as well as permit one to follow the initiation and development of ultrasonic cavitation and study nonlinear effects. The remote sensing ability and high sensitivity of focused ultrasonic receivers allow their practical use in biomedical acoustics for noninvasive measurements.