Effects of Subatmospheric Pressure and Dissolved Oxygen Content on Lesions in Ex Vivo Bovine Livers Induced by High Intensity Focused Ultrasound

Abstract

This study was aim at investigating the effects of subatmospheric pressure and dissolved oxygen content(DOC) on cavitation in tissue. This experiment put ex vivo bovine liver tissues which were degassed for 60 minutes into three different DOC degassed water, 1.0 mg/L, 1.5 mg/L and 2.0 mg/L, respectively. 1 MHz US with Isp equal to 11700 W/cm2 was used to exposure the degassed bovine livers under two ambient hydrostatic pressure(Pstat), atmospheric pressure(Pstat=1 bar) and subatmospheric pressure(Pstat=0.1 bar), with exposure time of 2 s, exposure depth of 2 cm. The hyperecho in focus before and after HIFU exposure were monitored by B mode ultrasound. The acoustic cavitaion signal was detected by passive cavitation detector (PCD) during the process of exposure. The results showed that the broadband noise under atmospheric pressure were all higher than that under subatmospheric pressure when keep DOC the same. Under atmospheric pressure, evident signals of broadband noise were appeared during HIFU exposure under three DOC condition, meanwhile the hyperecho was found in focus after exposing. Moreover, the intensity of broadband noise signal increased with the increase of DOC. Under subatmospheric pressure, cavitation just occurred under DOC of 2.0 mg/L, and only under DOC of 1.0 mg/L did not found hyperehco in focus. Results also demonstrated that lesions induced by HIFU increased with DOC under two Pstat, but the volume of lesions under atmospheric pressure were all larger than that under subatmospheric pressure when keep DOC the same. 1. The volume of lesion decrease with the decrease of DOC when keep Pstat constant. 2. Subatmospheric pressure would suppress cavitation in biological tissue during HIFU exposure. 3. The homogeneity of lesions in tissue was changed by cavitation.