The delayed-onset of inertial cavitation in tissue-mimicking agar phantom

Abstract Objective . Delayed-onset cavitation refers to inertial cavitation occurring in the middle of an applied ultrasound burst, rather than at its onset. In other words, the inertial cavitation threshold depends on the number of applied acoustic cycles. Understanding this phenomenon is important for improving the safety of biomedical ultrasound applications that utilize long ultrasound bursts, such as ultrasound stimulation. Although delayed-onset cavitation has been previously observed experimentally in agar-based tissue phantoms, its underlying mechanism has not been well understood. Approach. In this study, delayed-onset cavitation was first investigated in water and agar-based tissue phantoms. Then, a theoretical model was used to combine a viscoelastic bubble dynamics model with the rectified diffusion process to numerically demonstrate that delayed-onset cavitation is possible in agar-based tissue-mimicking phantom. Main result. Compared to cavitation in water, the increased viscoelasticity and existence of relatively large size cavitation nuclei in agar phantoms likely contribute to the delayed onset cavitation. Significance. The results underscore the need for further investigation of cycle-dependent inertial cavitation threshold criterion for biomedical ultrasound applications using long bursts in viscoelastic media.