Investigation into the Mechanisms of Tissue Atomization by High-Intensity Focused Ultrasound

Abstract

Ultrasonic atomization, or the emission of a fog of droplets, was recently proposed to explain tissue fractionation in boiling histotripsy. However, even though liquid atomization has been studied extensively, the mechanisms of tissue atomization remain unclear. In this paper, high-speed photography and overpressure were used to evaluate the role of bubbles in tissue atomization. As the static pressure increased, the degree of fractionation decreased, and the ex vivo tissue became thermally denatured. The effect of surface wetness on atomization was also evaluated in vivo and in tissue-mimicking gels where surface wetness was found to enhance atomization by forming surface instabilities that augment cavitation. In addition, experimental results indicated that wetting collagenous tissues, such as the liver capsule, allowed atomization to breach such barriers. These results highlight the importance of bubbles and surface instabilities in atomization and could be used to enhance boiling histotripsy for transition to clinical use.

Pulmonary Capillary Hemorrhage Induced by Acoustic Radiation Force Impulse Shear Wave Elastography in Ventilated Rats

“…Further research is needed to clarify PCH mechanisms. High intensity focused ultrasound directed upward at a liquid surface can produce fountains and atomization, phenomena that can be responsible for tissue fragmentation and might be involved in PCH [15–17,23]. We have found that present push pulses (limited to DUS MI<1.9) can produce fountains and atomization at a water or blood air interface [38].…”

“…Note that the application of PEEP was a test for the importance of very small pressures on the gas side of the pulmonary blood-air barrier, which oppose the small ultrasonic radiation surface pressure, and not a test for the cavitation mechanism of bioeffects. Ultrasonic cavitation does not appear to be responsible for DUS-PCH [13], and tests of the role of cavitation in bioeffects, for example in lung [22] or focused ultrasound atomization [23], require much higher static pressures > 1MPa (>10,000 cm H 2 O).…”

Histotripsy: the first noninvasive, non-ionizing, non-thermal ablation technique based on ultrasound

“…The other parameters used in boiling histotripsy are summarized in Table 1 . Tissue atomization has been proposed to be one of the mechanisms by which boiling histotripsy causes tissue damage [ 93 , 94 ]. At the tissue surface, boiling bubbles result in jetting against the tissue surface and fountain projectiles [ 91 , 95 ].…”

Diagnostic Ultrasound Safety Review for Point‐of‐Care Ultrasound Practitioners

“…Acoustic radiation force, generated as US energy is absorbed, or acoustic radiation pressure, generated when US reflects from a surface, can cause perturbation of tissue . The physical perturbations can be biologically substantial for high‐intensity focused US but are small for diagnostic US, with a minimal expectation of harm. Radiation forces can lead to fluid flow, which can be evident in a US image and useful for distinguishing cysts from tumors .…”