| Therapeutic ultrasound at high pulse-average intensity but with low duty cycle is a promising non-invasive modality for the treatment of the diseases for which present health care would perform surgery. As a surgical tool, high-intensity focused ultrasound (HIFU) possess numerous advantages including easier monitoring, precision, sharp borders, and minimal damage to the surrounding region, etc. The mechanical effect of inertial cavitation of bubble clouds that are excited and maintained by ultrasound pulses and able to fractionate tissue or liquefy a region is widely believed to be the main mechanism for this so-called histotripsy process. This inter-disciplinary research addresses the potential therapeutic applications in three types of biological tissues—agar that emulates organ tissue and envisions tumor, porcine muscle ex vivo, and biofilms that envision the infection on medical implants. Starting with the calibration procedure for our spherically-focused ultrasound source, this thesis work is mainly devoted to pursuing optimum exposure conditions in favor of treatment efficacy and efficiency. Depositing energy into a small focal region, HIFU covered a much wider one through a raster scanning pattern. So we experimentally investigated the effects of exposure time, scan step size, and burst period or pulse repetition frequency (PRF) on the lesion dimension inside agar or the cell destruction of P. aeruginosa and E. coli biofilms. Also, in our agar experiments, scan direction, agar stiffness and bending strength were used as additional study variables. This thesis work also involves the computer simulation of the temporal and spatial progression of gas void fraction since the activity of bubble clouds is directly linked with the lesion formation and/or bacteria destruction. |
