HISTOTRIPSY BUBBLE DYNAMICS IN ELASTIC, ANISOTROPIC TISSUE- MIMICKING PHANTOMS

anisotropic tissue such as tendon has proven resistant to mechanical fractionation by histo-tripsy, a subset of focused ultrasound that uses the creation, oscillation and collapse of cavitation bubbles to frac-tionate tissue. Our objective was to fabricate an optically transparent hydrogel that mimics tendon for evaluation of histotripsy bubble dynamics. Ex vivo bovine deep digital flexor tendons were obtained (n = 4), and varying formulations of polyacrylamide (PA), collagen and fibrin hydrogels (n = 3 each) were fabricated. Axial sound speeds were measured at 1 MHz for calculation of anisotropy. All samples were treated with a 1.5-MHz focused ultrasound transducer with 10-ms pulses repeated at 1 Hz (p+ = 127 MPa, p- = 35 MPa); treatments were monitored with passive cavitation imaging and high-speed photography. Dehydrated fibrin gels were found to be the most similar to tendon in cavitation emission energy (fibrin = 0.69 +/- 0.24, tendon = 0.64 +/- 0.19 [ pound 1010 V2]) and anisotropy (fibrin = 3.16 +/- 1.12, tendon = 19.4). Bubble cloud area in dehydrated fibrin (0.79 +/- 0.14 mm2) was significantly smaller than most other tested hydrogels. Finally, anisotropy was found to have moderately strong linear relationships with cavitation energy and bubble cloud size (r = -0.65 and -0.80, respectively). Dehydrated fibrin shows potential as a repeatable, transparent, tissue-mimicking hydrogel for evaluation of his-totripsy bubble dynamics in elastic, anisotropic tissues. (E-mail: jce29@psu.edu) (c) 2022 World Federation for Ultrasound in Medicine & Biology. All rights reserved.