Nonlinear acoustics in ultrasound metrology and other selected applications (original) (raw)

Nonlinear ultrasound propagation through layered liquid and tissue-equivalent media: computational and experimental results at high frequency

Physics in Medicine and Biology, 2006

Nonlinear propagation has been demonstrated to have a significant impact on ultrasound imaging. An efficient computational algorithm is presented to simulate nonlinear ultrasound propagation through layered liquid and tissueequivalent media. Results are compared with hydrophone measurements. This study was undertaken to investigate the role of nonlinear propagation in high frequency ultrasound micro-imaging. The acoustic field of a focused transducer (20 MHz centre frequency, f-number 2.5) was simulated for layered media consisting of water and tissue-mimicking phantom, for several widebandwidth source pulses. The simulation model accounted for the effects of diffraction, attenuation and nonlinearity, with transmission and refraction at layer boundaries. The parameter of nonlinearity, B/A, of the water and tissue-mimicking phantom were assumed to be 5.2 and 7.4, respectively. The experimentally measured phantom B/A value found using a finite-amplitude insert-substitution method was shown to be 7.4 ± 0.6. Relative amounts of measured second and third harmonic pressures as a function of the fundamental pressures at the focus were in good agreement with simulations. Agreement within 3% was found between measurements and simulations of the beam widths of the fundamental and second harmonic signals following propagation through the tissue phantom. The results demonstrate significant nonlinear propagation effects for high frequency imaging beams.

Theoretical and experimental high-frequency nonlinear ultrasound propagation through multilayered media

IEEE Ultrasonics Symposium, 2004, 2004

We present a new model of nonlinear ultrasound propagation through multilayered liquid/tissue media. This model includes the effects of diffraction, attenuation, and nonlinearity, with refraction and energy conservation at layer boundaries. It is capable of simulating pulsed and continuous wave propagation from sources of arbitrary geometry and excitation. Using this model, the acoustic field of a highfrequency circular focused transducer (1.5 mm aperture radius, f# 2.5) was simulated for two configurations, water only, and water-tissue phantom-water, and compared to the field measured with a high-frequency needle hydrophone, for 10 different source amplitudes of a transmitted Gaussian pulse (f 0 = 20 MHz, fractional bandwidth = 35%), ranging from 0.05 to 1 MPa. Very good agreement was found between simulated and measured fields in terms of relative amplitudes of the fundamental, second and third harmonics, beam widths and depth of fields, given the uncertainty in the experimental transmitted pulse amplitudes and hydrophone sensitivity above 40 MHz. Our model is capable of simulating realistic finite-amplitude propagation from highfrequency transducers through multilayered biological media. Its remarkable accuracy and efficiency makes it a very useful tool for the study of nonlinear ultrasonic fields, as well as for transducer design optimization.

Nonlinear propagation applied to the improvement of resolution in diagnostic medical ultrasound

The Journal of the Acoustical Society of America, 1997

Medical B-mode scanners operating under conditions typically encountered during clinical work produce ultrasonic wave fields that undergo nonlinear distortion. In general, the resulting harmonic beams are narrower and have lower sidelobe levels than the fundamental beam, making them ideal for imaging purposes. This work demonstrates the feasibility of nonlinear harmonic imaging in medical scanners using a simple broadband imaging arrangement in water. The ultrasonic system comprises a 2.25-MHz circular transducer with a diameter of 38 mm, a membrane hydrophone, also with a diameter of 38 mm, and a polymer lens with a focal length of 262 mm. These components are arranged coaxially giving an imaging geometry similar to that used in many commercial B-scanners, but with a receiver bandwidth sufficient to record the first four harmonics. A series of continuous wave and pulse-echo measurements are performed on a wire phantom to give 1-D transverse pressure profiles and 2-D B-mode images, respectively. The reflected beamwidths w n decrease as w n /w 1 ϭ1/n 0.78 , where n is the harmonic number, and the reflected sidelobe levels fall off quickly with increasing n. In imaging terms, these effects correspond to a large improvement in lateral resolution and signal-to-clutter ratio for the higher harmonics.

Measurement Of The Nonlinear Ultrasonic Parameter In Aqueous Solutions

This paper deals with the measurement of the nonlinear ultrasound coefficient  in aqueous solutions. Our aim is to show the possibility of using this parameter in ultrasound characterization of these solutions with the possibility of extending this technique to other complex media. The experimental determination of nonlinearity parameter is based on the quasi-linear approximation that allows us to derive an analytical expression of the second harmonic amplitude that takes into account the diffraction and the absorption effects. The experimental set up is composed of a piezoelectric disc transmitting at the fundamental frequency 2.2 MHz. The second harmonic is detected using a ring surrounding the disc and functioning at 4.4 MHz. The disc and the ring are both mounted on the same composed device and are both located in the same transversal plan to the propagation axis. The transmitted wave propagates through the sample and is detected by the receiver An appropriate signal processing...

Nonlinear Restoring Behavior of Therapeutic Ultrasound Transducers

Proc 5th International Symposium on Therapeutic Ultrasound

The behavior of a 1-3 piezocomposite transducer at high driving amplitudes and offresonance frequencies was investigated numerically and experimentally. By heuristically generating a numerical model of a simple resonator with a hard restoring force, a likely mechanism was identified for harmonic distortions in high power ultrasound transduction. Experimental observations of enhanced upper harmonic content in transducer response to a sinusoidal driving function were analyzed. This analysis revealed that a substantial proportion of the total pressure amplitude (at least 51%) was distributed into harmonics of the driving frequency, especially at frequencies that were below or above a characteristic resonance peak of the transducer. These results imply a need for more detailed and thorough evaluation of ultrasound transducers which are designed for high-intensity applications.

Moderately nonlinear ultrasound propagation in blood-mimicking fluid

Ultrasound in Medicine & Biology, 2004

In medical diagnostic ultrasound (US), higher than-in-water nonlinearity of body fluids and tissue usually does not produce strong nonlinearly distorted waves because of the high absorption. The relative influence of absorption and nonlinearity can be characterized by the Gol'dberg number ⌫. There are two limiting cases in nonlinear acoustics: weak waves (⌫ < 1) or strong waves (⌫ >> 1). However, at diagnostic frequencies in tissue and body fluids, the nonlinear effects and effects of absorption more likely are comparable (Gol'dberg number ⌫ Ϸ 1). The aim of this work was to study the nonlinear propagation of a moderately nonlinear US second harmonic signal in a blood-mimicking fluid. Quasilinear solutions to the KZK equation are presented, assuming radiation from a flat and geometrically focused circular Gaussian source. The solutions are expressed in a new simplified closed form and are in very good agreement with those of previous studies measuring and modeling Gaussian beams. The solutions also show good agreement with the measurements of the beams produced by commercially available transducers, even without special Gaussian

Nonlinear propagation effects on broadband attenuation measurements and its implications for ultrasonic tissue characterization

The Journal of the …, 1999

A study is presented in which the influence of the pressure amplitude of the incident pulse on the estimated frequency dependency of the attenuation coefficient is shown. First, the effect is demonstrated with a simple theoretical model for both transmission and reflection measurements. Simulations show that for both measurement techniques a high-amplitude incident pulse results in a biased estimate of the attenuation coefficient due to nonlinear interaction of the different frequency components of the incident pulse. It is shown that in transmission and reflection measurements the biases have opposite signs. The effect of bandwidth, central frequency, and phase of the incident pulse on this bias is investigated. Second, the effect is demonstrated both in vitro, using a broadband through-transmission substitution technique on a tissue mimicking gelatine phantom, and in vivo, using reflection measurements with standard clinical equipment. The experimental results agree well with the theoretical model. The relevance of this study for ultrasonic tissue characterization is shown.

Higher order nonlinear ultrasound propagation in tissue-simulation study

2002 IEEE Ultrasonics Symposium, 2002. Proceedings., 2002

Nonlinear wave propagation in tissue has been simulated using typical propagation parameters for liver. The results indicate that the amplitude level of higher order harmonics can exceed the level of the second harmonic component. In that case detection of the higher order components can be achieved with increased signal to noise ratio due to the fact that the amplitude of the 3 rd order component can be higher than the 2 nd harmonic and the fact that the 3 rd order mixing component falls into the middle of the transducer bandwidth. Odd order harmonic components are of particular interest since they create spectral mixing products at the fundamental frequency. Therefore, transmission and reception can operate around the same center frequency.

Broadband Reduction of the Second Harmonic Distortion During Nonlinear Ultrasound Wave Propagation

Ultrasound in Medicine and Biology, 2010

Ultrasound contrast harmonic imaging and detection techniques are hampered by the harmonic distortion of the ultrasound wave caused by the nonlinearities of the medium. To increase the discrimination between the tissue and ultrasound contrast agents at higher harmonics, we investigate a tissue harmonic suppression technique. The main attention of the research is the signal that is introduced at the source and is constructed out of several discrete frequency components from the second harmonic band. Therefore, this method was coined as the multiple component second harmonic reduction signal or multiple component SHRS. By adjusting the amplitude and phase of discrete components and simultaneously propagating multiple component SHRS with the imaging signal, the nonlinear distortion of the ultrasound waveform is considerably reduced. Using the numerical simulation, the optimal parameters for multiple component SRHS were deduced. The simulations results were corroborated in the water tank experiments and showed 40 dB reduction with respect to the fundamental, covering up to 75% of the entire second harmonic band. In the other series of experiments with the clinically used contrast agent, the uniform increase in agent-to-tissue ratio of 7.4 dB over a relatively large region of imaging was observed. The use of the proposed method in the everyday clinical practice can improve discrimination between the tissue and the contrast agent in harmonic imaging. (