Investigation of intensity thresholds for ultrasound tissue erosion

Our previous studies have shown that short intense pulses delivered at certain pulse repetition frequencies (PRF) can achieve localized, clean erosion in soft tissue. In this paper, the intensity thresholds for ultrasound induced erosion and the effects of pulse intensity on erosion characterized by axial erosion rate, perforation area and volume erosion rate were investigated on in vitro porcine atrial wall tissue. Ultrasound pulses with a 3-cycle pulse duration and a 20-kHz PRF were delivered by a 788-kHz single element focused transducer. ISPPA values of 1000 to 9000 W/cm2 were tested. Results show the following: (1) the estimated intensity threshold for generating erosion was at ISPPA of 3220 W/cm2; (2) the axial erosion rate increased with higher intensity at ISPPA ≤ 5000 W/cm2, while decreased with higher intensity at ISPPA ≥ 5000 W/cm2; and (3) the perforation area and the volume erosion rate increased with higher intensity.