Biomedical Engineering Thoraxcenter, Erasmus Medical Center, Rotterdam, The Netherlands.
Ultrasound Med Biol. 2011 Jun;37(6):958-70. doi: 10.1016/j.ultrasmedbio.2011.02.017. Epub 2011 Apr 30.
The subharmonic vibration of BR14 (Bracco Research S.A., Geneva, Switzerland) contrast agent microbubbles is investigated within the preferable frequency range for carotid ultrasound imaging (8-12 MHz). The response of the bubbles was recorded optically with an ultra-fast recording camera (Brandaris 128) at three acoustic pressures (50, 100 and 120 kPa). The vibration of the microbubbles was measured as a function of the excitation frequency and its frequency content was determined. Among 390 recordings, 40% showed subharmonic oscillations. It was observed that for smaller microbubbles (diameter < 3 μm) the frequency of the maximum subharmonic response increases for increasing pressures (shell hardening) opposite to what has been reported for larger microbubbles (3 μm < diameter < 15 μm). These findings are well predicted by the model proposed by Marmottant et al. (2005) after including the dilatational shell viscosity of the microbubbles measured by Van der Meer et al. (2007), which indicates a marked shear-thinning behavior of the phospholipid shell.
BR14（Bracco Research S.A.，瑞士日内瓦）造影微泡的次谐波振动在颈动脉超声成像的优选频率范围内（8-12MHz）进行了研究。使用超快速记录相机（Brandaris 128）在三个声压（50、100 和 120kPa）下对气泡的响应进行了光学记录。微泡的振动作为激励频率的函数进行了测量，并确定了其频率内容。在 390 次记录中，有 40%显示出次谐波振荡。观察到，对于较小的微泡（直径<3μm），随着压力（壳变硬）的增加，最大次谐波响应的频率增加，这与较大微泡（3μm<直径<15μm）的情况相反。这些发现与 Marmottant 等人提出的模型（2005 年）很好地吻合，该模型包括了 Van der Meer 等人（2007 年）测量的微泡的扩张壳粘度，这表明磷脂壳具有明显的剪切稀化行为。
