Vlaisavljevich Eli, Xu Zhen, Maxwell Adam, Mancia Lauren, Zhang Xi, Lin Kuang-Wei, Duryea Alexander, Sukovich Jonathan, Hall Tim, Johnsen Eric, Cain Charles
IEEE Trans Ultrason Ferroelectr Freq Control. 2016 Aug;63(8):1064-1077. doi: 10.1109/TUFFC.2016.2565612. Epub 2016 May 10.
Histotripsy is an ultrasound ablation method that depends on the initiation of a dense cavitation bubble cloud to fractionate soft tissue. Previous work has demonstrated that a cavitation cloud can be formed by a single acoustic pulse with one high amplitude negative cycle, when the negative pressure amplitude exceeds a threshold intrinsic to the medium. The intrinsic thresholds in soft tissues and tissue phantoms that are water-based are similar to the intrinsic threshold of water over an experimentally verified frequency range of 0.3-3 MHz. Previous work studying the histotripsy intrinsic threshold has been limited to experiments performed at room temperature (~20°C). In this study, we investigate the effects of temperature on the histotripsy intrinsic threshold in water, which is essential to accurately predict the intrinsic thresholds expected over the full range of in vivo therapeutic temperatures. Based on previous work studying the histotripsy intrinsic threshold and classical nucleation theory, we hypothesize that the intrinsic threshold will decrease with increasing temperature. To test this hypothesis, the intrinsic threshold in water was investigated both experimentally and theoretically. The probability of generating cavitation bubbles was measured by applying a single pulse with one high amplitude negative cycle at 1 MHz to distilled, degassed water at temperatures ranging from 10°C-90°C. Cavitation was detected and characterized by passive cavitation detection and high-speed photography, from which the probability of cavitation was measured vs. pressure amplitude. The results indicate that the intrinsic threshold (the negative pressure at which the cavitation probability=0.5) significantly decreases with increasing temperature, showing a nearly linear decreasing trend from 29.8±0.4 MPa at 10˚C to 14.9±1.4 MPa at 90˚C. Overall, the results of this study support our hypothesis that the intrinsic threshold is highly dependent upon the temperature of the medium, which may allow for better predictions of cavitation generation at body temperature in vivo and at the elevated temperatures commonly seen in high intensity focused ultrasound (HIFU) regimes.
组织粉碎术是一种超声消融方法,它依靠密集空化泡云的产生来破碎软组织。先前的研究表明,当负压幅值超过介质固有的阈值时,单个具有一个高幅值负周期的声脉冲就能形成空化云。在0.3 - 3 MHz这个经过实验验证的频率范围内,软组织和水基组织仿体中的固有阈值与水的固有阈值相似。先前关于组织粉碎术固有阈值的研究仅限于在室温(约20°C)下进行的实验。在本研究中,我们探究了温度对水中组织粉碎术固有阈值的影响,这对于准确预测在体内治疗的整个温度范围内预期的固有阈值至关重要。基于先前对组织粉碎术固有阈值的研究和经典成核理论,我们假设固有阈值会随着温度升高而降低。为了验证这一假设,我们从实验和理论两方面研究了水中的固有阈值。通过向温度范围为10°C至90°C的蒸馏脱气水中施加一个1 MHz的具有一个高幅值负周期的单脉冲,来测量产生空化泡的概率。通过被动空化检测和高速摄影来检测和表征空化现象,据此测量空化概率与压力幅值的关系。结果表明,固有阈值(空化概率 = 0.5时的负压)随着温度升高而显著降低,呈现出从10˚C时的29.8±0.4 MPa到90˚C时的14.9±1.4 MPa的近似线性下降趋势。总体而言,本研究结果支持了我们的假设,即固有阈值高度依赖于介质的温度,这可能有助于更好地预测体内体温以及高强度聚焦超声(HIFU)治疗中常见的高温下的空化产生情况。