Biomedical subjects

Meng-Xing Tang

Publications and source records attributed to Meng-Xing Tang.

3 recordsLinked to original sources

PubMed2007

Frequency and pressure dependent attenuation and scattering by microbubbles.

The aim of this study was to evaluate experimentally the degree of pressure dependence of attenuation and scattering by microbubbles at low acoustic pressures with an empirical nonlinear model. In addition, the pressure dependency over a range of frequencies (1 to 5 MHz) has been studied. A series of transmission and scattering measurements were made with the microbubble SonoVue, using an automated system. Results show that, within the pressure range studied, attenuation as a result of the microbubble is pressure-dependent, whereas no such dependence of scattering was detectable. The pressure dependence of attenuation for SonoVue was found to be most significant at 1.5 MHz. The scattering is shown to be the highest at the lowest insonation frequency, around 1 approximately 1.25 MHz, and then decreases with frequency.

Humans↗

PubMed2006

Nonlinear propagation of ultrasound through microbubble contrast agents and implications for imaging.

Microbubble contrast agents produce nonlinear echoes under ultrasound insonation, and current imaging techniques detect these nonlinear echoes to generate contrast agent images accordingly. For these techniques, there is a potential problem in that bubbles along the ultrasound transmission path between transducer and target can alter the ultrasound transmission nonlinearly and contribute to the nonlinear echoes. This can lead to imaging artefacts, especially in regions at depth. In this paper we provide insight, through both simulation and experimental measurement, into the nonlinear propagation caused by microbubbles and the implications for current imaging techniques. A series of investigations at frequencies below, at, and above the resonance frequency of microbubbles were performed. Three specific effects on the pulse propagation (i.e., amplitude attenuation, phase changes, and harmonic generation) were studied. It was found that all these effects are dependent on the initial pulse amplitude, and their dependence on the initial phase of the pulse is shown to be insignificant. Two types of imaging errors are shown to result from this nonlinear propagation: first, that tissue can be misclassified as microbubbles; second, the concentration of microbubbles in the image can be misrepresented. It is found that these imaging errors are significant for all three pulse frequencies when the pulses transmit through a microbubble suspension of 6 cm in path length. It also is found that the first type of error is larger at the bubble resonance frequency.

Computer Simulation↗

PubMed2005

Pressure-dependent attenuation with microbubbles at low mechanical index.

It has previously been shown that the attenuation of ultrasound (US) by microbubble contrast agents is dependent on acoustic pressure (Chen et al. 2002). Although previous studies have modelled the pressure-dependence of attenuation in single bubbles, this paper investigates this subject by considering a bulk volume of bubbles together with other linear attenuators. Specifically, a new pressure-dependent attenuation model for an inhomogeneous volume of attenuators is proposed. In this model, the effect of the attenuation on US propagation is considered. The model was validated using experimental measurements on the US contrast agent Sonovue. The results indicate, at low acoustic pressures, a linear relationship between the attenuation of Sonovue, measured in dB, and the insonating acoustic pressure.

Humans↗