The effect of the phase of transmission on contrast agent echoes

摘要

Ultrasound contrast agents consist of a gas bubble, encapsulatednby a shell for stabilization. The shell dampens the fluctuations in thenbubble radius when insonified. The detection of contrast microbubblesnduring a medical examination can indicate whether a region is perfusednwith blood. Here, the authors consider the effect of the phase ofnsonification signal on the backscatter by the bubble echo. Byntransmitting two short pulses of ultrasound with opposite phases, thenauthors demonstrate that a unique pair of echoes can be generated by ansingle microbubble, and that the properties of these echoes may benuseful in the discrimination of bubble and tissue echoes. Specifically,nthe significant echo amplitude begins coincident with each transmittednrarefactional half-cycle, and the mean frequency of this echo depends onnthe transmitted phase. When rarefaction is transmitted first for a 2.25nMHz signal, the mean frequency is 0.8 MHz higher for an albumin-shellednbubble and 0.9 MHz higher for a lipid-shelled bubble. The experimentalnresults agree with the predictions of the Gilmore-Akulichev equation