On the prediction of monocyte deposition in abdominal aortic aneurysms using computational fluid dynamics.

In abdominal aortic aneurysm disease, the aortic wall is exposed to intense biological activity involving inflammation and matrix metalloproteinase-mediated degradation of the extracellular matrix. These processes are orchestrated by monocytes and rather than affecting the aorta uniformly, damage and weaken focal areas of the wall leaving it vulnerable to rupture. This study attempts to model numerically the deposition of monocytes using large eddy simulation, discrete phase modelling and near-wall particle residence time.

Acquisition of 3-D arterial geometries and integration with computational fluid dynamics.

A system for acquisition of 3-D arterial ultrasound geometries and integration with computational fluid dynamics (CFD) is described. The 3-D ultrasound is based on freehand B-mode imaging with positional information obtained using an optical tracking system. A processing chain was established, allowing acquisition of cardiac-gated 3-D data and segmentation of arterial geometries using a manual method and a semi-automated method, 3D meshing and CFD.

A dual-phantom system for validation of velocity measurements in stenosis models under steady flow.

A dual-phantom system is developed for validation of velocity measurements in stenosis models. Pairs of phantoms with identical geometry and flow conditions are manufactured, one for ultrasound and one for particle image velocimetry (PIV). The PIV model is made from silicone rubber, and a new PIV fluid is made that matches the refractive index of 1.

Hydrodynamic glide efficiency in swimming.

The glide is a major part of starts, turns and the stroke cycle in breaststroke. Glide performance, indicated by the average velocity, can be improved by increasing the glide efficiency, that is, the ability of the body to minimise deceleration. This paper reviews the factors that affect glide efficiency.

A method to estimate wall shear rate with a clinical ultrasound scanner.

A simple technique to estimate the wall shear rate in healthy arteries using a clinical ultrasound scanner has been developed. This method uses the theory of fully developed oscillatory flow together with a spectral Doppler trace and an estimate of mean arterial diameter. A method using color flow imaging was compared with the spectral Doppler method in vascular phantoms and found to have errors that were on average 35% greater.

Characterization of an abdominal aortic velocity waveform in patients with abdominal aortic aneurysm.

Haemodynamics studies of abdominal aortic aneurysm require data on the velocity in the normal section of the aorta. Centreline velocity waveforms were measured in abdominal aortic aneurysm patients proximal to the aneurysm using spectral Doppler ultrasound. Characteristic points were automatically found on 21 of the waveforms and their parameters were used to create an archetypal centreline velocity waveform.

An arterial wall motion test phantom for the evaluation of wall motion software.

Increasing cardiovascular disease has led to new ultrasound methods of assessing artery disease such as arterial wall motion measurement. To validate arterial wall motion software, we developed a mechanically-controlled wall motion test phantom with straight upper and lower agar tissue mimicking material layers that resemble an artery cross section. The wall separation, displacements and wall velocities and accelerations can be controlled within physiologically realistic levels.

Distribution of wall shear rate throughout the arterial tree: a case study.

The generally accepted assumption that the arterial system remodels itself to maintain constant wall shear stress throughout is based on Murray's law, utilising the principle of minimum work for steady flow. However, blood flow in the human arterial system is pulsatile. In this work we outline a method allowing for estimation of wall shear rate in arteries using the flow waveforms as the input signal and estimate wall shear rates in the common carotid, brachial, and femoral arteries to determine the uniformity of distribution of wall shear rates throughout the arterial system.

Laser Doppler anemometry measurements of the shear stresses on ultrasonic contrast agent microbubbles attached to agar.

Ultrasonic contrast agents are currently being developed to target and bind to specific areas of interest such as atheromous plaque. A microbubble has been developed in-house which can be targeted to attach to specific cell-lines. To assess the feasibility of using the microbubble in vivo, the shear stresses which the bound microbubbles can withstand need to be known.