Experimental Investigation of the Effect of Stiffness, Exposure Time and Scan Direction on the Dimension of Ultrasound Histotripsy Lesions

Histotripsy uses high-intensity focused ultrasound to create energetic bubble clouds inside tissue to liquefy a region and has the advantages of higher contrast B-mode monitoring and sharp borders. This study experimentally investigated the effects of stiffness, exposure time and scan direction on the size of histotripsy-induced lesions in agar samples. A targeted region 0.45 cm wide (lateral) and 0.6 cm deep (axial) was scanned with the step sizes of 0.075 cm and 0.3 cm, respectively. The single-element spherically focused source (1.1 MHz, 6.34 cm focal length, f/1) had the peak compressional and rarefactional pressures of approximately 102 and 17 MPa. Pulses consisted of 20-cycle sine wave tone bursts with a burst period of 3 ms and exposure time of 15, 30 or 60 s. Also, both inward and outward scan direction were tested along the beam axis. The liquefied lesions generally had a larger size than the initially targeted region with larger sizes corresponding to softer agar and longer exposure. There was not a statistically significant difference in the lesion size with scan direction.