Size Measurement of Tissue Debris Particles Generated from Pulsed Ultrasound Cavitational Therapy – Histotripsy

Xu, Zhen; Fan, Zhenzhen; Hall, Timothy L.; Winterroth, Frank; Fowlkes, J. Brian; Cain, Charles A.

doi:10.1016/j.ultrasmedbio.2008.09.002

« Previous Next »Ultrasound in Medicine and Biology
Volume 35, Issue 2 , Pages 245-255, February 2009

Size Measurement of Tissue Debris Particles Generated from Pulsed Ultrasound Cavitational Therapy – Histotripsy

Zhen Xu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
- Address correspondence to: Zhen Xu, 2200 Bonisteel Boulevard, 1107 Carl A. Gerstacker Building, Ann Arbor, MI 48109-2099, USA
Zhenzhen Fan
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
Timothy L. Hall
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
Frank Winterroth
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
J. Brian Fowlkes
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
- Department of Radiology, University of Michigan, Ann Arbor, MI, USA
Charles A. Cain
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
- Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, USA

Received 10 April 2008; received in revised form 13 June 2008; accepted 1 September 2008. published online 25 November 2008.

Abstract

Extensive mechanical tissue fractionation can be achieved using successive high intensity ultrasound pulses (“histotripsy”). Histotripsy has many potential medical applications where noninvasive tissue removal is desired (e.g., tumor ablation). There is a concern that debris generated by histotripsy-induced tissue fractionation might be an embolization hazard. The aim of this study is to measure the size distribution of these tissue debris particles. Histotripsy pulses were produced by a 513-element 1 MHz array transducer, an 18-element 750 kHz array transducer and a 788 kHz single element transducer. Peak negative pressures of 11 to 25 MPa, pulse durations of 3 to 50 cycles, pulse repetition frequencies of 100 Hz to 2 kHz were used. Tissue debris particles created by histotripsy were collected and measured with a particle sizing system. In the resulting samples, debris <6 μm in diameter constituted >99% of the total number of tissue particles. The largest particle generated by one of the parameter sets tested was 54 μm in diameter, which is smaller than the clinic filter size (100 μm) used to prevent embolization. The largest particles generated using other parameter sets were larger than 60 μm but the value could not be specified using our current setup. Exposures with shorter pulses produced lower percentages of large tissue debris (>30 μm) in comparison to longer pulses. These results suggest that the tissue debris particle size distribution is adjustable by altering acoustic parameters if necessary. (E-mail: zhenx@umich.edu)

Key Words: Histotripsy, Therapeutic ultrasound, Cavitation, Pulsed ultrasound, Tissue fractionation, Embolization