Other resources

Experimental and Numerical Investigation of Wire Waveguides for Therapeutic Ultrasound Angioplasty

Declan Noone (Thesis) — Tue, 13 Mar 2012 05:14:36 PDT

Therapeutic ultrasound angioplasty is an emerging minimally invasive cardiovascular procedure for disrupting atherosclerotic lesions using small diameter wire waveguides. The lesions are damaged through a combination of direct ablation, pressure waves, cavitation and acoustic streaming caused by distal-tip displacements at ultrasonic frequencies. Numerical and experimental methods are used to investigate the outputs of the wire waveguides during ultrasonic activation. A commercially available generator and acoustic horn are used in combination with Nickel-Titanium (NiTi) wire waveguides in this study. A laser sensor is used to measure the frequency and amplitude output of the distal tip of the wire waveguide, and this is compared to amplitude estimations obtained using an optical microscope. Power is observed to affect both amplitude and frequency. Clinical devices will require long, flexible waveguides with diameters small enough to access the coronary arteries. A finite element model is used to design tapered sections in long wire waveguides in order to achieve low profile distal geometry, and improve ultrasonic wave transmission. These tapered sections reduce the wire waveguide diameter in two stages, firstly from 1 to 0.35mm and then from 0.35 to 0.2, while increasing the amplitude of the ultrasonic wave by factors of 2.85 and 1.75, respectively. The numerical model also showed damping could potentially be a significant problem in long untapered wire waveguides (>1.5m). Experimental ablation trials were conducted using the tapered long wire waveguides, including assessment of the effect of various combinations of bend radii and bend angles. The waveguide was found to perform well, but increased power levels were required to transmit ultrasound through tortuous waveguide configurations.

A Test Method for Optimal Micro-screen Drum Filter Selection

Eoin Dolan et al. — Tue, 13 Mar 2012 02:44:52 PDT

In order to meet increasing demand for seafood worldwide Recirculation Aquaculture Systems (RAS) are frequently used. These systems are susceptible to contamination by waste matter including faecal material in the water. It is imperative that this material is removed from the system. The maintenance of good water quality is a pre-requisite to the success of the operation. Negligence in this area will adversely affect animal growth rates and also the economic performance of the system.

Micro-screen drum filters are a popular solution for the removal of this material (Cripps, Simon J. and Bergheim, Asbjørn., 2000). These screens are nominally rated by their screen aperture size measured in microns.

A common issue with the selection of this equipment is in relation to the many variables that influence filter performance. For simplicity, vendors have rationalised selection criteria for filters to the flow capacity at each end of the potential solids loading spectrum, without any reference to a specific culture species.

This paper outlines a technique for accurate micro-screen drum filter selection for site and species specific applications using simple equipment, allowing the identification of an optimal filtration solution, in terms of cost and filtration performance. It also evaluates the potential of cake filtration for increased filter mechanical efficiency performance,

Highlights

This paper sets out to establish;

Optimal drum filter selection
Particle size distribution of suspended solids in a RAS
Feasibility and effectiveness of cake filtration in mechanical efficiency and flow rate terms.

It is envisaged that this new methodology can be adopted by aquaculturists to address the need within the aquaculture industry for documented and optimised species specific filtration solutions.

Production of Anatomical Models from CT Scan Data

John Brennan — Thu, 24 Mar 2011 07:00:13 PDT

Rapid Prototyping (RP) technology was conceived in the mid 1980s as a method of manufacturing models, particularly to support the design of new motor vehicles. However as early as 1995 the potential to take data from medical scanners and generate models of patient anatomy to assist clinicians plan complex surgical procedures had been recognised, albeit by researchers rather than the mainstream medical industry. Over the last 15 years the production of preoperative planning models has increased dramatically and moreover, the potential to produce customised implants recognised.

Although RP technology is now established in the medical field work is still on going to develop new applications (the majority of cases still reside in craniomaxillofacial field), explore the use of different RP methods and overall improve the efficiency of the approach.

In this project the latest medical data processing software tools will be used to generate models for preoperative planning and also medical training and the results reviewed. A comprehensive literature review in the field has been conducted and publications in the medical scanning, RP, preoperative planning, biomaterials, customised medical implants and jigs are presented and discussed. Several case studies which are particularly pertinent to the trials undertaken by the author have been identified and incorporated into the report and explained in detail in order to illustrate the capability, potential and flexibility of this technology within the medical sector.

Experimental and Numerical Investigation of Therapeutic Ultrasound Angioplasty

Graham P. Gavin et al. — Fri, 13 Nov 2009 11:12:44 PST

Therapeutic ultrasound angioplasty is an emerging minimally invasive cardiovascular surgical procedure that involves the delivery of ultrasonic displacements to the distal-tip of small diameter wire waveguides. The ultrasonic distal-tip displacements affect atherosclerotic plaque and thrombus by direct contact ablation, pressure wave components and cavitation, in addition to an acoustic streaming event around the distal-tip. This study uses experimental and numerical methods to investigate ultrasonic displacements in wire waveguides and the effect the distal-tip displacements have on the surrounding fluid. An experimental therapeutic ultrasound wire waveguide apparatus is described that delivers displacements to the distal-tip of 1.0 mm and tapered 0.35 mm diameter nickel-titanium (NiTi) waveguides. The operating frequency of the apparatus has been experimentally determined to be 23.5 kHz and for the power settings tested delivers displacements of up to 85 µm peak-to-peak (p-p) to the distal-tip of 1.0 mm diameter waveguides. The apparatus has been shown to directly ablate calcified materials with a stiffer response when compared with atherosclerotic plaques and to generate cavitation and acoustic streaming. A coupled fluid-structure numerical model of the waveguide and fluid surrounding the distal-tip has been developed that predicts the waveguide displacements and stresses along the entire length of the wire waveguide. The structural results of the model have been validated against experimental measurements of the displacements of the waveguide with the inclusion of a constant damping value of 4.5%. The fluid results of the model predict the pressure amplitudes developed in the surrounding fluid and compare closely with values reported in literature. The model predicts the distal-tip displacements required to cause cavitation, a major disruptive event, and has been compared with experimental observations made with the ultrasonic wire waveguide apparatus. The waveguide numerical model will prove a valuable design tool in the further development and improvement of this emerging cardiovascular technology.