0
RESEARCH PAPERS

A Coupled Fluid-Structure Model of a Therapeutic Ultrasound Angioplasty Wire Waveguide

[+] Author and Article Information
Graham P. Gavin, M. S. Hashmi, Garrett B. McGuinness

School of Mechanical and Manufacturing Engineering, Dublin City University, Dublin, Ireland

Finbar Dolan

 Medtronic Vascular Ltd., Galway, Ireland

J. Med. Devices 1(4), 254-263 (Aug 31, 2007) (10 pages) doi:10.1115/1.2812424 History: Received December 07, 2006; Revised August 31, 2007

Ultrasonic longitudinal displacements, delivered to the distal tips of small diameter wire waveguides, are known to be capable of disrupting complicated atherosclerotic plaques during vascular interventions. These ultrasonic displacements can disrupt plaques not only by direct contact ablation but also by pressure waves, associated cavitation, and acoustic streaming developed in the surrounding blood and tissue cavities. The pressure waves developed within the arterial lumen appear to play a major role but are complex to predict as they are determined by the distal tip output of the wire waveguide (both displacement and frequency), the geometric features of the waveguide tip, and the effects of biological fluid interactions. This work describes a numerical linear acoustic fluid-structure model of an ultrasonic wire waveguide and the blood surrounding the distal tip. The model predicts a standing wave structure in the wire waveguide, including stresses and displacements, and requires the incorporation of a damping constant. The effects on waveguide response of including an enlarged ball tip at the distal end of the waveguide, designed to enhance cavitation and surface contact area, are investigated, in addition to the effects of the surrounding blood on the resonant response of the waveguide. The model also predicts the pressures developed in the acoustic fluid field surrounding the ultrasonic vibrating waveguide tip and can predict the combinations of displacements, frequencies, and waveguide geometries associated with cavitation, an important event in the disruption of plaque. The model has been validated against experimental displacement measurements with a purpose built 23.5 kHz nickel-titanium wire waveguide apparatus and against experimental pressure measurements from the literature.

Copyright © 2007 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

Diagram of therapeutic ultrasound wire waveguide apparatus showing ultrasonic generator, converter and horn, and flexible small diameter wire waveguide

Grahic Jump Location
Figure 2

(a) Comparison of numerical and experimental distal-tip displacements for multiple wire waveguide lengths between 188mm and 303mm. Applied proximal displacement is 32μm. Damping in the waveguide model is 4.5% (15). (b) Comparison of numerical and experimental distal-tip displacements for multiple wire waveguide lengths between 188mm and 303mm. Applied proximal displacement is 46μm. Damping in the waveguide model is 4.5% (15).

Grahic Jump Location
Figure 3

Image of wire waveguide displacement obtained by the optical microscope and image analysis software. Initial length of mark was 9.2μm and the image streak length of 63.17μm giving a displacement of approximately 54μm peak to peak.

Grahic Jump Location
Figure 4

Diagram of a uniform rod, of length l, with an input displacement motion of u=bsinωt. Adapted from Steidel (17).

Grahic Jump Location
Figure 5

Diagram relating to the pressure field developed around an oscillating sphere. Adapted from Nyborg (14).

Grahic Jump Location
Figure 6

Distal section of acoustic fluid-structure model of wire waveguide with 1.0mm spherical ball tip

Grahic Jump Location
Figure 7

(a) Comparison of numerical, experimental, and analytical displacements for a wire waveguide of length 288mm (near antiresonant), with no damping and with 4.5% damping. Applied proximal displacement is 32μm. (b) Comparison of numerical predicted stresses for a wire waveguide of length 288mm (near antiresonant), with no damping and with 4.5% damping. Applied proximal displacement is 32μm.

Grahic Jump Location
Figure 8

(a) Comparison of numerical and experimental displacements for a wire waveguide of length 273mm (near antiresonant) with 4.5% damping. Applied proximal displacement is 32μm. (b) Numerical predicted stresses for a wire waveguide of length 273mm (near antiresonant) with 4.5% damping. Applied proximal displacement is 32μm.

Grahic Jump Location
Figure 9

Predicted numerical displacements response for a wire waveguide of length 500mm and 0.35mm diameter between 22kHz and 26kHz, with no distal ball tip and ball tips of 1.0mm and 1.5mm. Input displacement is 100μm. Damping is 4.5%.

Grahic Jump Location
Figure 10

Predicted numerical displacements response for a wire waveguide of length 500mm and 0.35mm diameter between 22kHz and 26kHz, with a 1.0mm ball tip. Damping is 4.5%.

Grahic Jump Location
Figure 11

Predicted pressure field around distal section of acoustic fluid-structure model of wire waveguide with 2.46mm spherical ball tip and distal-tip displacement of 130m peak to peak at 22.5kHz. Model based on device described by Makin and Everbach (13).

Grahic Jump Location
Figure 12

(a) Experimental pressures and predicted numerical pressure field ahead of 2.46mm spherical ball tip, in the region 12–100mm, and distal-tip displacement of 130m at 22.5kHz. Model based on device described by Makin and Everbach (13). (b) Experimental pressures and predicted numerical pressure field ahead of 2.46mm spherical ball tip, in the region 0–12mm, and distal-tip displacement of 130m at 22.5kHz. Model based on device described by Makin and Everbach (13).

Grahic Jump Location
Figure 13

Predicted pressure field ahead of wire waveguide (distance 0–1.0mm) with 1.0mm and 1.5mm spherical ball tips and multiple distal-tip displacements

Grahic Jump Location
Figure 14

Predicted pressure field ahead of 1.0mm diameter wire waveguide with a flat distal tip and distal tip displacements of 27μm, 54μm, and 68μm

Grahic Jump Location
Figure 15

Images of the distal tip of a 1.0mm diameter wire waveguide vibrating at 23.5kHz and with distal-tip displacements of 35μm, 46μm, 54μm, 63μm, 76μm, and 85μm

Grahic Jump Location
Figure 16

Image of fluid motion (acoustic streaming) around the distal tip of a 1.0mm diameter wire waveguide vibrating at 23.5kHz and with distal-tip displacements of (a) below predicted cavitation threshold=35μm and (b) above predicted cavitation threshold=76μm

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In