IEEE ultrasonics symposium

This paper investigates nonlinear B/A parameter imaging in ultrasound echo mode. First, the B/A estimation methods which can be extended to echo mode are identified. The finite amplitude approaches are found to be excellent candidates to assess the nonlinear parameter because of their experimental simplicity, supported by a strong mathematical background. Second, three nonlinear coefficient measurement methods, thus far proposed for applications in homogeneous media, are extended to heterogeneous media. In particular, the simulations show that the extended comparative method (ECM) offers the best results when the probe diffraction effects are taken into consideration. The first experimental images obtained by applying the ECM for two different phantoms are also presented, showing the feasibility of B/A imaging.

Extensions of nonlinear B/A parameter imaging methods for echo mode

The nonlinear parameter of ultrasound B/A has shown to be a useful diagnostic parameter, reflecting medium content, structure, and temperature. Despite its recognized values, B/A is not yet used as a diagnostic tool in the clinic due to the limitations of current measurement and imaging techniques. This review presents an extensive and comprehensive overview of the techniques developed for B/A measurement of liquid and liquid-like media (e.g., tissue), identifying the methods that are most promising from a clinical perspective. This work summarizes the progress made in the field and the typical challenges on the way to B/A estimation. Limitations and problems with the current techniques are identified, suggesting directions that may lead to further improvement. Since the basic theory of the physics behind the measurement strategies is presented, it is also suited for a reader who is new to nonlinear ultrasound.

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A review on B/A measurement methods with a clinical perspective

Numerical simulations based on the nonlinear parabolic wave equation are used to investigate time reversal of sound beams radiated by unfocused and focused sources. Emphasis is placed on nonlinear propagation distortion in the time-reversed beam, and specifically its effect on field reconstruction. Distortion of this kind, due to amplification during time reversal, has been observed in recent experiments [A. P. Brysev et al., Acoust. Phys. 44, 641–650 (1998)]. Effects of diffraction introduced by time-reversal mirrors with finite apertures are also considered. It is shown that even in the presence of shock formation, the ability of time reversal to retarget most of the energy on the source or focal region of the incident beam is quite robust.

Time-reversed sound beams of finite amplitude.

Magneto-acoustic ceramics for parametric sound wave phase conjugators

The results of theoretical and experimental studies of application of parametric wave phase conjugation (WPC) for nonlinear detection of isoechogenic phantoms and for ultrasonic velocimetry of flows are reported. Experimental WPC harmonic imaging of isoechogenic phantoms in water was demonstrated on an example of cells filled with a mixture of water and methyl alcohol. Variation of methanol concentration allows obtaining some mixtures with varied nonlinear parameters while their linear acoustic impedance remains close to the water's one. Analysis of harmonics of phase conjugate waves (PCW) in automatically con-focal WPC-system provides reliable detection of the phantoms. According to the theoretical predictions the contrasts of images are comparable with, or even stronger, than the ratio of nonlinear parameters of a phantom and its surrounding medium. 3D-simulation of propagation of PCW in heterogeneously nonlinear and moving media is developed. Break of time reversal invariance of WPC in moving media is proposed as a principle of detection and velocimetry of flows. The results of experimental linear and harmonic imaging of flows in water are presented in comparison with theoretical description.

Nonlinear Acoustic Imaging of Isoechogenic Objects and Flows Using Ultrasound Wave Phase Conjugation

The possibility for the application of the method of parametric phase conjugation of ultrasonic waves in measuring the velocity of moving objects and flows is investigated. Results of experimental measurements of the Doppler frequency shift are presented for a low-frequency wave (1 MHz) generated by phase-conjugate waves (10 MHz and 11 MHz) propagating in opposite directions in the presence of a moving scatterer. The super high sensitivity of the phase of the low-frequency wave to variations in the spatial position of the scatterer is used to measure the velocity of the object. The presence of flows in the region of propagation of phase-conjugate waves returned leads to an uncompensated Doppler shift of the phase of the phase-conjugate wave at the primary radiation source. The implementation of this feature of ultrasonic phase conjugation for the detection and measurement of the flow velocities in a liquid is demonstrated experimentally.

Detection of moving objects and flows in liquids by ultrasonic phase conjugation

Nonlinear propagation of a quasi-plane conjugate ultrasonic beam

The potential of ultrasonic velocimetry and mapping for liquid flows in a model and real biological media is demonstrated experimentally and theoretically using the technique of parametric phase conjugation of sound. The basis of the proposed method is violation of invariance of an acoustic field with respect to time reversal in a moving medium that leads to an uncompensated phase shift of a phase-conjugate wave at a transmitter-receiver array. The principles for application of nonlinear acoustic effects for improving the reconstruction precision for the field of flow velocities are discussed.

Diagnostics and doppler tomography of liquid flows with ultrasonic phase conjugation

The results of using of wave phase conjugation in Doppler velocimetry of liquid flows are presented. The increase of sensitivity and signal-to-noise ratio of phase shift measurements by means of nonlinear interaction of phase conjugate ultrasonic waves is demonstrated. Doppler effect, wave phase conjugation, nonlinear interaction

Yu. V. Pyl’nov

Papers

Nonlinear Acoustic Imaging of Isoechogenic Objects and Flows Using Ultrasound Wave Phase Conjugation

Detection of moving objects and flows in liquids by ultrasonic phase conjugation

Nonlinear propagation of a quasi-plane conjugate ultrasonic beam

Diagnostics and doppler tomography of liquid flows with ultrasonic phase conjugation

Flow velocity measurements by means of nonlinear interaction of phase conjugate ultrasonic waves