Controlled ultrasound tissue erosion: the effects of tissue type, exposure parameters and the role of dynamic microbubble activity

Previous studies have shown that ultrasound can mechanically remove tissue in a highly controlled, localized manner. The dependence of the erosion process on tissue type and exposure parameters was investigated. In particular, the effects of tissue elasticity, gas saturation and pulse intensity were explored. Moreover, an enhanced and rapidly changing backscatter was highly correlated with the erosion process. A statistical method was developed to detect "initiation" and "extinction" of the highly backscattering environment. The relationship between initiation and erosion, and the effects of pulse intensity and gas saturation on time to initiation (initiation delay time) were investigated. Results show the following: (1) erosion is faster with softer tissue; (2) erosion rate does not change significantly for increasing gas saturation, but becomes more consistent with increased gas saturation; (3) erosion rate does not change significantly for increasing intensity; (4) the presence or absence of initiation of enhanced backscatter successfully predicted erosion or lack of erosion at a rate of 98.9%; (5) initiation delay time is shorter with higher intensity and higher gas saturation; and (6) once initiated by high intensity pulses, the highly backscattering environment and erosion can be sustained using a significantly lower intensity than that required to initiate the process.