Acoustic cavitation plays an important role in the medical treatment using high intensity focused ultrasound (HIFU), but unnecessarily strong cavitation also could deform the morphology and enlarge the size of lesions. It is known that the increase of ambient hydrostatic pressure (Pstat) can control the acoustic cavitation but the question how decrease of Pstat and dissolved oxygen concentration (DOC) influences the strength of cavitation has not been thoroughly answered.
Ex vivo bovine liver tissues were immersed in degassed water with different DOC of 1.0 mg/L, 1.5 mg/L and 2.0 mg/L. Ultrasound (US) of 1 MHz and the spatial and temporal average intensity (Isata) of 6500 W/cm2 was used to expose two groups of in vitro bovine livers for two seconds; one group was under atmospheric pressure (Pstat = 1 bar) and the other was under sub-atmospheric pressure (Pstat = 0.1 bar). Acoustic cavitation was detected by a passive cavitation detector (PCD) during the exposure process. Echo signals at the focal zone of HIFU were monitored by B-mode ultrasound imaging before and after exposure.
The results demonstrated a significant difference of broadband acoustic emissions from the cavitation bubbles, echo signals on B mode image, morphology of lesions under various condition of ambient pressure and DOC. The lesion volume in tissue was increased with the increase of ambient pressure and DOC.
Cavitation could be suppressed through sub-atmospheric pressure and low DOC level in liver tissue, which could provide a method of controlling cavitation in HIFU treatment to avoid unpredictable lesions.