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Understanding the limitations of ultrasonic backscatter measurements from microbubble populations.

Abstract：

:Despite over ten years of in vitro investigations of ultrasound contrast agents, the level of understanding of their behaviour in ultrasound fields is limited. Several problems associated with these investigations, particular to the nature of contrast agents, are discussed. Using a commercial scanner the RF normalized backscatter of two different contrast agents (Definity and Quantison) was measured at different suspension concentrations and acoustic pressures. Both contrast agents scattered ultrasound nonlinearly and the backscatter showed a dependence on acoustic pressure. In order to assess the average behaviour of the agents across the range of acoustic pressures and microbubble concentrations the experimental data were fitted to a theoretically acceptable model using nonlinear regression analysis. The analysis showed that both the backscatter and the attenuation of the Quantison suspensions displayed a higher order of dependence on acoustic pressure than the Definity suspensions. It was also discovered that Quantison microbubbles did not demonstrate uniform behaviour across the acoustic pressure range. At lower acoustic pressures the behaviour could not follow a model similar to that which predicted the behaviour at higher acoustic pressures, which was mainly due to the fact that free bubbles were released in a fashion dependent on acoustic pressure. The fact that two different populations of scatterers exist in the same suspensions makes the assessment of the behaviour of the particular agent impossible with the high concentrations that are commonly used. Very low concentration suspensions whereby single scattering events can be monitored should be more useful. In conclusion, the approach of using high microbubble concentrations in order to investigate the properties of ultrasonic contrast agents is limited in that the results of such studies cannot be used to understand the behaviour of single microbubbles.

journal_name

Phys Med Biol

journal_title

Physics in medicine and biology

authors

Sboros V,Ramnarine KV,Moran CM,Pye SD,McDicken WN

doi

10.1088/0031-9155/47/23/313

subject

Has Abstract

pub_date

2002-12-07 00:00:00

pages

4287-99

issue

eissn

0031-9155

issn

1361-6560

journal_volume

pub_type

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Understanding the limitations of ultrasonic backscatter measurements from microbubble populations.