Bevan Peter D, Karshafian Raffi, Tickner E Glenn, Burns Peter N
Department of Medical Biophyscs, University of Toronto, Toronto, ON, Canada.
Ultrasound Med Biol. 2007 Nov;33(11):1777-86. doi: 10.1016/j.ultrasmedbio.2007.05.013. Epub 2007 Jul 25.
The goal of this study was to assess the threshold of disruption and subsequent time-course of acoustic response of four experimental nitrogen-filled polymer-shelled microbubbles. Using an in vitro measurement system, a sequence of low-amplitude detection pulses measured the change in echo caused by a high-amplitude disruption pulse on a dilute suspension of bubbles. Detection pulses were transmitted 0.5 ms before disruption and between 1 and 200 ms after disruption. Separate transducers, aligned confocally and orthogonally, were used to transmit and receive bubble echoes. After disruption, all agents demonstrated a transient increase in scattered power. Above the disruption threshold, highly echogenic, nonlinear scatterers were observed. Their echoes slowly disappeared after disruption with median decay times from 7.4 to 13.6 ms, calculated by fitting to a mono-exponential decay. This is consistent with a process wherein the shell is disrupted, releasing the gas and generating free gas bubbles, which cause high-amplitude nonlinear scattering followed by relatively slow diffusion of the gas into solution. This picture has been observed optically with single bubbles and differs from the concept of "stimulated acoustic emission" from disrupted bubbles.
本研究的目的是评估四种实验性充氮聚合物壳微泡的破裂阈值及随后的声学响应时间进程。使用体外测量系统，一系列低振幅检测脉冲测量了高振幅破裂脉冲对稀气泡悬浮液产生的回波变化。检测脉冲在破裂前0.5毫秒以及破裂后1至200毫秒之间发射。使用共焦和正交排列的单独换能器来发射和接收气泡回波。破裂后，所有试剂的散射功率均出现短暂增加。高于破裂阈值时，观察到高回声、非线性散射体。破裂后，它们的回波缓慢消失，通过拟合单指数衰减计算得出的中位衰减时间为7.4至13.6毫秒。这与壳破裂、释放气体并产生游离气泡的过程一致，游离气泡会引起高振幅非线性散射，随后气体相对缓慢地扩散到溶液中。这种情况已在单个气泡的光学观察中看到，并且与破裂气泡的“受激声发射”概念不同。
