High intensity focused ultrasound lithotripsy with cavitating microbubbles

Abstract

In the medical ultrasound field, microbubbles have recently been the subject of much interest. Controlling actively the effect of the microbubbles, a novel therapeutic method has been investigated. In this paper, our works on high intensity focused ultrasound (HIFU) lithotripsy with cavitating microbubbles are reviewed and the cavitation detection method to optimize the HIFU intensity is investigated. In the HIFU lithotripsy, collapse of the cloud cavitation is used to fragment kidney stones. Cloud cavitation is potentially the most destructive form of cavitation. When the cloud cavitation is acoustically forced into a collapse, it has the potential to concentrate a very high pressure. For the control of the cloud cavitation collapse, a novel two-frequency wave (cavitation control [C-C] waveform) is designed; a high-frequency ultrasound pulse (1-4 MHz) to create the cloud cavitation and a low-frequency trailing pulse (500 kHz) following the high-frequency pulse to force the cloud into collapse. High-speed photography showed the cavitation collapse on the stone and the shock-wave emission from the cloud. In vitro erosion tests of model and natural stones were also conducted. In the case of model stones, the erosion rate of the C-C waveform showed a distinct advantage with the combined high- and low-frequency waves over either wave alone. For the optimization of the high-frequency ultrasound intensity, the subharmonic acoustic pressure was examined. The results showed relationship between the subharmonic pressure from cavitating bubbles induced by the high-frequency ultrasound and eroded volume of the model stones. Natural stones were eroded and most of the resulting fragments were less than 1 mm in diameter. The method has the potential to provide a novel lithotripsy system with small fragments and localized cavitating bubbles on a stone.

High-frequency linear rheology of hydrogels probed by ultrasound-driven microbubble dynamics

“…For therapeutic purposes, microbubbles can be delivered to tissues, for instance by acoustic droplet vaporisation, 3,4 or bubbles can be generated directly inside tissues, for instance in high-intensity focused ultrasound and lithotripsy. [5][6][7] The behaviour of bubbles embedded in tissues has been exploited for diagnostic purposes to measure the rheological properties of the tissue, such as in tissue palpation and elastography. 8 In these methods, ultrasound with frequency far above the resonance frequency of the bubbles is applied, to avoid bubble oscillations and only cause a displacement due to acoustic radiation force.…”

Cavitation-Enhanced Mechanical Effects and Applications

“…While the use of HIFU in lithotripsy is relatively recent (Ikeda et al 2006;Yoshizawa et al 2009;Duryea et al 2011;Harper et al 2014;Maxwell et al 2015), it has some significant advantages over SWL. HIFU can be focused much more precisely than shock waves such that it can enhance the damage at the desired site while reducing collateral tissue damage.…”

“…They proposed a two-frequency combined waveform method to concentrate very high pressures on stone surfaces within the localized cavitation area, and they utilized the collapse of a cavitation cloud to fragment the stones (Yoshizawa et al 2009;Matsumoto et al 2005;Ikeda et al 2006). Figure 5.29 shows a schematic of their cavitation control lithotripsy (CCL) method.…”

Potential and problems in ultrasound-responsive drug delivery systems

“…Because ultrasound contrast agents can be used to image the blood pool, URDDS have been investigated as targeted therapy to the vasculature, including thrombolysis, 114 lithotripsy, 115 chemotherapy, 116 anti-inflammatory treatment, 117 stem cell transplantation 118,119 and gene therapy for coronary heart disease. In recent years, some researchers have started investigating URDDS as therapy targeted to the brain.…”