Quantitative analysis of Doppler spectrum modifications yielded bycontrast agents insonified at high pressure

摘要

In this report, the authors consider the modifications yielded innthe Doppler spectrum when acoustic fields of increasing intensities arenapplied to encapsulated gas bubbles. Their in vitro experimental resultsnshow that the spectrum bandwidth is nearly proportional to the incidentnacoustic pressure, when its amplitude is maintained below about 200 kPa.nAt higher pressure levels, it even may happen that, in a steady,nunidirectional flow (which should generate only positive Dopplernfrequencies), the Doppler spectrum is enlarged up to the point thatnnegative Doppler shifts also are produced. Possible explanations innterms of either radiation force or streaming are discussed for thisnasymmetrical bandwidth enlargement