Institut Langevin, ESPCI ParisTech, CNRS UMR 7587, INSERM U979, Université Denis Diderot, Paris VII, 10 Rue Vauquelin, 75005 Paris, France.
Phys Med Biol. 2011 Nov 21;56(22):7001-15. doi: 10.1088/0031-9155/56/22/001. Epub 2011 Oct 21.
Gas nuclei exist naturally in living bodies. Their activation initiates cavitation activity, and is possible using short ultrasonic excitations of high amplitude. However, little is known about the nuclei population in vivo, and therefore about the rarefaction pressure required to form bubbles in tissue. A novel method dedicated to in vivo investigations was used here that combines passive and active cavitation detection with a multi-element linear ultrasound probe (4-7 MHz). Experiments were performed in vivo on the brain of trepanated sheep. Bubble nucleation was induced using a focused single-element transducer (central frequency 660 kHz, f-number = 1) driven by a high power (up to 5 kW) electric burst of two cycles. Successive passive recording and ultrafast active imaging were shown to allow detection of a single nucleation event in brain tissue in vivo. Experiments carried out on eight sheep allowed statistical studies of the bubble nucleation process. The nucleation probability was evaluated as a function of the peak negative pressure. No nucleation event could be detected with a peak negative pressure weaker than -12.7 MPa, i.e. one order of magnitude higher than the recommendations based on the mechanical index. Below this threshold, bubble nucleation in vivo in brain tissues is a random phenomenon.
气体核在活体中自然存在。它们的激活会引发空化活动，可以通过高幅度的短超声激振来实现。然而，人们对活体中的核群体知之甚少，因此也不知道在组织中形成气泡所需的稀疏压力。这里使用了一种专门用于体内研究的新方法，该方法将被动和主动空化检测与多阵元线性超声探头（4-7 MHz）结合使用。实验在开颅的绵羊大脑中进行。使用聚焦单阵元换能器（中心频率 660 kHz，f 数= 1）驱动高功率（高达 5 kW）电脉冲爆震来诱导气泡成核，电脉冲爆震由两个周期组成。实验结果表明，连续的被动记录和超快主动成像可用于检测活体脑组织中的单个成核事件。对八只绵羊进行的实验允许对气泡成核过程进行统计学研究。将成核概率评估为峰值负压的函数。在峰值负压低于-12.7 MPa 时，无法检测到成核事件，这比基于机械指数的建议高一个数量级。低于此阈值，活体脑组织中的气泡成核是一种随机现象。
