State Key Laboratory of Ultrasound Engineering in Medicine Co-Founded by Chongqing and the Ministry of Science and Technology, College of Biomedical Engineering, Chongqing Key Laboratory of Biomedical Engineering, Chongqing Medical University, Chongqing 400016, PR China.
National Engineering Research Center of Ultrasound Medicine, Chongqing 401121, PR China.
Ultrason Sonochem. 2017 May;36:36-41. doi: 10.1016/j.ultsonch.2016.11.001. Epub 2016 Nov 9.
It is well-known that acoustic cavitation associated with the high intensity focused ultrasound (HIFU) treatment often would change the morphology and size of lesions in its treatment. In most studies reported in literature, high ambient hydrostatic pressure was used to suppress the cavitation completely. Investigation of the effects by varying the ambient hydrostatic pressure (P) is still lacking. In this paper, the effects of HIFU on lesions in ex vivo bovine liver specimens under various P are systematically investigated. A 1MHz HIFU transducer, with an aperture diameter of 70mm and a focal length of 55mm, was used to generate two groups US exposure of different acoustic intensities and exposure time (6095W/cm×8s and 9752W/cm×5s), while keeping the same acoustic energies per unit area (48760J/cm). The peak acoustic negative pressures (p) of the two groups were p=9.58MPa and p=10.82MPa, respectively, with the difference p=p-p=1.24MPa. A passive cavitation detection (PCD) was used to monitor the ultrasonic cavitation signal during exposure of the two groups. The US exposures were done under the following ambient hydrostatic pressures, P: atmospheric pressure, 0.5MPa, 1.0MPa, 1.5MPa, 2.0MPa, 2.5MPa and3.0MPa, respectively. The result of PCD showed that there was a statistically significant increase above background noise level in broadband emissions at dose of 9752W/cm×5s, but not at dose of 6095W/cm×8s under atmospheric pressure; i.e., the acoustic cavitation took place for p but not for p when under atmospheric pressure. The results also showed that there was no statistically difference of the morphology and size of lesions for 6095W/cm×8s exposure under the aforementioned different ambient hydrostatic pressures. But the lesions generated at 9752W/cm×5s exposure under P=atmospheric pressure, 0.5MPa, 1.0MPa (all of them are less than p), were larger than those under 1.5MPa, 2.0MPa, 2.5MPa and 3.0MPa (all of them are over than p) which were consistence with 6095W/cm×8s group. It was concluded that when P>p, the acoustic cavitation was suppressed and prompted that there was no need to elevate P higher than p to suppress the acoustic cavitation in tissue, just need P higher than p.
众所周知，与高强度聚焦超声（HIFU）治疗相关的声空化通常会改变病变的形态和大小。在文献中报道的大多数研究中，使用高环境静水压力完全抑制空化。然而，关于通过改变环境静水压力（P）来进行的影响的研究仍然缺乏。在本文中，我们系统地研究了在不同 P 下 HIFU 对离体牛肝标本中的病变的影响。使用孔径为 70mm 和焦距为 55mm 的 1MHz HIFU 换能器，产生两组不同声强和暴露时间的 US 暴露（6095W/cm×8s 和 9752W/cm×5s），同时保持相同的单位面积声能（48760J/cm）。两组的峰值声负压力（p）分别为 p=9.58MPa 和 p=10.82MPa，差值为 p=p-p=1.24MPa。使用被动空化检测（PCD）在两组的 US 暴露期间监测超声空化信号。US 暴露分别在以下环境静水压力下进行，P：大气压力、0.5MPa、1.0MPa、1.5MPa、2.0MPa、2.5MPa 和 3.0MPa。PCD 的结果表明，在大气压力下，在剂量为 9752W/cm×5s 时，宽带发射的背景噪声水平以上有统计学意义的增加，但在剂量为 6095W/cm×8s 时则没有；即，在大气压力下，当 p 时发生声空化，但当 p 时则不发生。结果还表明，在上述不同环境静水压力下，6095W/cm×8s 暴露下的病变形态和大小没有统计学差异。但是，在 P=大气压力、0.5MPa、1.0MPa（均小于 p）下产生的 9752W/cm×5s 暴露的病变大于在 1.5MPa、2.0MPa、2.5MPa 和 3.0MPa（均大于 p）下产生的病变，这与 6095W/cm×8s 组一致。结论是，当 P>p 时，声空化受到抑制，并表明不需要将 P 升高到高于 p 以抑制组织中的声空化，只需要 P 高于 p 即可。
