Design Issues for Therapeutic Ultrasound Angioplasty Waveguides

Therapeutic ultrasound angioplasty is a new minimally invasive cardiovascular procedure for disrupting atherosclerotic lesions. Mechanical energy is transmitted in the form of ultrasound waves via long, flexible wire waveguides navigated to the lesion site through the vascular system. The underpinning principle of this technology is that plaque may be disrupted through a combination of direct contact ablation, pressure waves, cavitation and acoustic streaming, which all depend on the amplitude and frequency of displacements at the distal tip of the wire waveguide. This study identifies a number of key design issues for clinical devices of this type, and describes testing procedures to measure selected performance characteristics. A commercially available generator (100 W) and acoustic horn are used in combination with Nickel-Titanium (NiTi) wire waveguides. A laser sensor system was constructed to measure the frequency and amplitude output at the distal tip of the wire waveguide, and this was compared to amplitude estimations obtained using an optical microscope. Power was observed to affect both output amplitude and frequency. A finite element model has been previously developed to simulate the transmission of ultrasound waves in short wire waveguides. In this study, this methodology has been extended to the design of long, tapered wires for realistic clinical applications. Trials were conducted using these wire waveguides, demonstrating the ablation of model calcified materials accessed via long wire waveguides