DISTAL TIP PRESSURES & ACOUSTIC STREAMING IN VIBRATING GUIDEWIRES

INTRODUCTION
High frequency mechanical vibrations (20-50 kHz) applied to slender wires have been shown to disrupt thrombus and fibrous and calcified plaques. Advanced manufacturing techniques can achieve complex geometric features, such as tapering and distal tip geometries on wires, while still facilitating the transmission of vibrational energy (Anamagh et al.). These vibrating guidewires disrupt plaque tissue through direct contact ablation and acoustic effects such as pressure wave components, acoustic streaming and potentially, cavitation (Yao et al.).
Acoustic pressure amplitudes near the tip are directly related to the onset of cavitation and also contribute to secondary effects like streaming. Morse proposed a solution for the pressures around an oscillating sphere, as shown in Equation 1,
𝑃𝑚𝑎𝑥= 2𝜋2𝜌𝑅𝑓2𝑑(𝑅2𝑐𝑜𝑠𝜃𝑟2) (eqn. 1)
,where ρ is the fluid density, R is the radius of the oscillating tip, f is the frequency of oscillations and d is the tip displacement amplitude. The terms in brackets account for spatial distribution around the sphere.
Acoustic streaming occurs when the diverging waves from the vibrating tip are attenuated by the fluid media, resulting in a momentum transfer to the fluid. This results in a unidirectional flow field in the proximity of the tip.
MATERIALS AND METHODS
A modelling approach is proposed where initially the acoustic pressure field around an oscillating tip is solved (ANSYS Harmonic Acoustic) and the acoustic intensity is calculated. This will be verified against the solution proposed by Morse and used to determine operating parameters sufficient to cause cavitation.
It has also been proposed in the literature that the momentum applied to the fluid, that results in streaming, can be calculated as shown in Equation 2,
𝐹= 2 𝛼𝐼𝑐 (eqn. 2)
,where F is force per unit volume, I is the acoustic intensity, c is the speed of sound in the fluid and α is the sound attenuation in the fluid (at the appropriate frequency).
Using the relationship in Equation 2, the momentum term is calculated and applied to a CFD model of the tip of a guidewire (ANSYS Fluent) in a realistic bounding environment representing an arterial wall and distal blockage.
RESULTS
The predicted acoustic pressures around a vibrating distal tip are shown Figure 1. A parametric study for a range of frequencies, distal tip amplitudes and wire geometries was conducted to better understand some of the design criteria and constraints in vibrating guidewire design.
Figure 1 Pressure distribution around a vibrating guidewire tip.
DISCUSSION
Knowledge of the acoustic pressure amplitudes allow for the prediction of the onset of cavitation. Further, using the technique discussed, the acoustic streaming flow velocities can be modelled. Flow visualisation was also performed to qualitatively assess the resulting flow field.
REFERENCES
Stone (et al.), Ultrasonics, 152, 2025.
Anamagh (et al.), Int. J. Comp. Meth. in Eng. Sci. and Mech., (in print) , 2025.
Yao (et al.), Ultrasonics Sonochemistry, 121, 2025.
Morse P.M. Vibration and sound, Acoustic Society of America, 27: 311-326, 1981.
ACKNOWLEDGEMENT
This work is funded under a DTIF award managed by the Department of Enterprise, Trade and Employment and administered by Enterprise Ireland.