title: High speed imaging of bubble clouds generated in pulsed ultrasound cavitational therapy--histotripsy.
abstract: Our recent studies have demonstrated that mechanical fractionation of tissue structure with sharply demarcated boundaries can be achieved using short (< 20 micros), high intensity ultrasound pulses delivered at low duty cycles. We have called this technique histotripsy. Histotripsy has potential clinical applications where noninvasive tissue fractionation and/or tissue removal are desired. The primary mechanism of histotripsy is thought to be acoustic cavitation, which is supported by a temporally changing acoustic backscatter observed during the histotripsy process. In this paper, a fast-gated digital camera was used to image the hypothesized cavitating bubble cloud generated by histotripsy pulses. The bubble cloud was produced at a tissue-water interface and inside an optically transparent gelatin phantom which mimics bulk tissue. The imaging shows the following: (1) Initiation of a temporally changing acoustic backscatter was due to the formation of a bubble cloud; (2) The pressure threshold to generate a bubble cloud was lower at a tissue-fluid interface than inside bulk tissue; and (3) at higher pulse pressure, the bubble cloud lasted longer and grew larger. The results add further support to the hypothesis that the histotripsy process is due to a cavitating bubble cloud and may provide insight into the sharp boundaries of histotripsy lesions.
authors.affiliation: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, USA. zhenx@umich.edu
authors.forename: Zhen
authors.initials: Z
authors.lastname: Xu
authors.forename: Mekhala
authors.initials: M
authors.lastname: Raghavan
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Hall
authors.forename: Ching-Wei
authors.initials: CW
authors.lastname: Chang
authors.forename: Mary-Ann
authors.initials: MA
authors.lastname: Mycek
authors.forename: J Brian
authors.initials: JB
authors.lastname: Fowlkes
authors.forename: Charles A
authors.initials: CA
authors.lastname: Cain
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005740:Gases / Q000032:analysis*; D008096:Lithotripsy / Q000295:instrumentation* / Q000379:methods*; D045423:Microbubbles; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D014463:Ultrasonography / Q000295:instrumentation* / Q000379:methods*
chemical_list: D005740:Gases