IEEE Trans Ultrason Ferroelectr Freq Control. 2014 Feb;61(2):325-40. doi: 10.1109/TUFFC.2014.6722617.
Histotripsy produces tissue fractionation through dense energetic bubble clouds generated by short, high-pressure, ultrasound pulses. When using pulses shorter than 2 cycles, the generation of these energetic bubble clouds only depends on where the peak negative pressure (P-) exceeds the intrinsic threshold of the medium (26 to 30 MPa in soft tissue with high water content). This paper investigates a strategic method for precise lesion generation in which a low-frequency pump pulse is applied to enable a sub-threshold high-frequency probe pulse to exceed the intrinsic threshold. This pump-probe method of controlling a supra-threshold volume can be called dual-beam histotripsy. A 20-element dual-frequency (500-kHz and 3-MHz elements confocally aligned) array transducer was used to generate dual-beam histotripsy pulses in red blood cell phantoms and porcine hepatic tissue specimens. The results showed that when sub-intrinsic-threshold pump (500-kHz) and probe (3-MHz) pulses were applied together, dense bubble clouds (and resulting lesions) were only generated when their peak negative pressures combined constructively to exceed the intrinsic threshold. The smallest reproducible lesion varied with the relative amplitude between the pump and probe pulses, and, with a higher proportion of the probe pulse, smaller lesions could be generated. When the propagation direction of the probe pulse relative to the pump pulse was altered, the shape of the produced lesion changed based on the region that exceeded intrinsic threshold. Because the low-frequency pump pulse is more immune to attenuation and aberrations, and the high-frequency probe pulse can provide precision in lesion formation, this dual-beam histotripsy approach would be very useful in situations in which precise lesion formation is required through a highly attenuative and aberrative medium, such as transcranial therapy. This is particularly true if a small low-attenuation acoustic window is available for the high-frequency probe transducer.
声声处理通过短而高压的超声脉冲产生密集的高能气泡云来实现组织分割。当使用短于 2 个周期的脉冲时，这些高能气泡云的产生仅取决于峰值负压（P-）超过介质固有阈值（高含水量软组织中的 26 至 30MPa）的位置。本文研究了一种精确产生病变的策略方法，即应用低频泵脉冲以使亚阈值高频探测脉冲超过固有阈值。这种控制超阈值体积的泵-探测方法可以称为双束声声处理。使用 20 单元双频（500kHz 和 3MHz 单元共焦排列）换能器在红细胞幻影和猪肝组织标本中产生双束声声处理脉冲。结果表明，当应用亚固有阈值的泵（500kHz）和探测（3MHz）脉冲时，只有当它们的峰值负压相叠加并超过固有阈值时，才会产生密集的气泡云（和由此产生的病变）。可重复产生的最小病变随泵和探测脉冲之间的相对幅度而变化，并且随着探测脉冲的比例增加，可以产生更小的病变。当探测脉冲相对于泵脉冲的传播方向改变时，产生的病变形状会根据超过固有阈值的区域而改变。由于低频泵脉冲对衰减和像差更具免疫力，而高频探测脉冲可以提供病变形成的精度，因此这种双束声声处理方法在需要通过高衰减和像差介质精确形成病变的情况下非常有用，例如经颅治疗。如果高频探测换能器有一个小的低衰减声窗，这种情况尤其如此。
