An experimental study of particle sedimentation using ultrasonic speckle velocimetry

Ultrasonic speckle velocimetry (USV) is a non-invasive technique that allows the measurement of fluid velocity in flow and also that of powders under sedimentation. To improve the USV method, we studied the sedimentation of polymethyl methacrylate and silica particles in water. Then, we built a sedimentation cell and characterized the diameter distribution of the particles. Subsequently, we carried out a specific study to optimize the USV procedure, the signal processing and data analysis. Space and temporal resolution and USV dynamics are also discussed with regard to the optimization conditions. We found that USV is a useful technique to measure velocities between 10−5 and 1 m s−1, using appropriate ultrasonic transducers. The space resolution is fixed by the length and the percentage of overlapping of the analyzed speckle windows and varies between 48 and 536 μm for the different studied particle families. Furthermore, we found that a 0.1 ns temporal resolution could be obtained after a zero padding signal processing. In the context of our sedimentation experiments, we showed that the velocities measured by USV are in close agreement with those measured by particle image velocimetry and theory

Ultrasonic Doppler measurement of renal artery blood flow

An extensive evaluation of the practical and theoretical limitations encountered in the use of totally implantable CW Doppler flowmeters is provided. Theoretical analyses, computer models, in-vitro and in-vivo calibration studies describe the sources and magnitudes of potential errors in the measurement of blood flow through the renal artery, as well as larger vessels in the circulatory system. The evaluation of new flowmeter/transducer systems and their use in physiological investigations is reported

Development of a Complex Flow Phantom for Diagnostic Imaging

Literature and market analysis have highlighted the lack of flow phantom technologies able to challenge innovative medical imaging devices, such as Ultrasound and Magnetic Resonance. A novel, cost-effective, compact and robust Complex Flow Phantom prototype was proposed. The design relies on the generation of stable, reproducible, predictable and controllable vortex rings. Vortex rings were chosen because bring together high stability and physiological relevance. The design was tested with multiple and independent measurement methods under challenging working conditions. Overall, it demonstrated to produce reproducible flows with variability always lower than +/- 10 %. This variability was assessed with regards to translational velocity, however, macro-flow reproducibility implies micro-flow stability. Computational Fluid Dynamics (CFD) and optical/video acquisitions were used as first methods to independently validate two early prototypes operating in air and water. CFD overall well approximate theoretical predictions but accuracy was insufficient to provide a reference standard. Overall, the early prototypes demonstrated encouraging stability and a Vortex Ring based Complex Flow Phantom prototype was manufactured. Laser PIV acquisitions were performed to establish flow reference standard values. Optical/video acquisitions were performed and results were compared with Laser PIV to assess the rigour of the methods. Results obtained by the two different measurement methods on two identically manufactured but different systems showed credible consistency. Conventional and advanced (Vector Flow Imaging) Ultrasound acquisitions were also performed on the design. An instrumentation pack was designed and is provided as tool for self-calibrating the phantom and for estimating flow reference values under different generating conditions. An MRI compatible version of the phantom was manufactured and was tested in laboratory. Design and experiments are supported by journal article and conference proceeding publications, poster and oral presentation in international conferences. The phantom is purchasable from Leeds Test Objects Ltd or can be manufactured in laboratory following the specifications provided

The use of ultrasound for detecting particles suspended in lubricant and hydraulic fluids

Imperial Users onl

Analytical and experimental comparisons between the frequency-modulated–frequency-shift measurement and the pulsed-wave–time-shift measurement Doppler systems

In previous publications, a new echo-ranging Doppler system based on transmission of repetitive coherent frequency-modulated (FM) sinusoids in two different implementations was presented. One of these implementations, the frequency-modulated-frequency-shift measurement (FM-fsm) Doppler system is, in this paper, compared with its pulsed-wave counterpart, the pulsed-wave-time-shift measurement (PW-tsm) Doppler system. When using transmitted PW and FM signals with a Gaussian envelope, the parallelism. between the two systems can be stated explicitly and comparison can be made between the main performance indices for the two Doppler systems. the performance of the FM and PW Doppler systems is evaluated by means of numerical simulation and measurements of actual flow profiles. the results indicate that the two Doppler systems have very similar levels of performance

Design and conduct of 'Xtreme Alps' : a double-blind, randomised controlled study of the effects of dietary nitrate supplementation on acclimatisation to high altitude

The study of healthy human volunteers ascending to high altitude provides a robust model of the complex physiological interplay that emulates human adaptation to hypoxaemia in clinical conditions. Nitric oxide (NO) metabolism may play an important role in both adaptation to high altitude and response to hypoxaemia during critical illness at sea level. Circulating nitrate and nitrite concentrations can be augmented by dietary supplementation and this is associated with improved exercise performance and mitochondrial efficiency. We hypothesised that the administration of a dietary substance (beetroot juice) rich in nitrate would improve oxygen efficiency during exercise at high altitude by enhancing tissue microcirculatory blood flow and oxygenation. Furthermore, nitrate supplementation would lead to measurable increases in NO bioactivity throughout the body. This methodological manuscript describes the design and conduct of the ‘Xtreme Alps’ expedition, a double-blind randomised controlled trial investigating the effects of dietary nitrate supplementation on acclimatisation to hypobaric hypoxia at high altitude in healthy human volunteers. The primary outcome measure was the change in oxygen efficiency during exercise at high altitude between participants allocated to receive nitrate supplementation and those receiving a placebo. A number of secondary measures were recorded, including exercise capacity, peripheral and microcirculatory blood flow and tissue oxygenation. Results from this study will further elucidate the role of NO in adaption to hypoxaemia and guide clinical trials in critically ill patients. Improved understanding of hypoxaemia in critical illness may provide new therapeutic avenues for interventions that will improve survival in critically ill patients

Spectral analysis of blood velocity in the human fetus

None provided

Ultrasonic blood flow detection: Doppler techniques for obstetrics

Ultrasonic Doppler techniques have been developed for the detection of uterine blood flow. The work was undertaken to provide a noninvasive method for the study of foetal haemodynamics.The operation of the continuous wave and the pulsed wave Doppler instruments and the factors which influence their performance are discussed. The different types of Doppler signal extraction techniques which can be used with the pulsed wave Doppler are described. A design for a 2.5 MHz pulsed wave Doppler instrument is presented. The results of in vivo and in vitro trials with this instrument are presented.A blood flow instrument specially designed for examining blood flow in the pregnant uterus is described. It consists of a real time ultrasonic scanner of rotating transducer design used in conjunction with the above types of Doppler instrument. In vivo evaluation of this equipment is presented.A novel type of continuous wave Doppler instrument, the intersecting zone Doppler is described. This device overcomes the problem of lack of localisation normally associated with the continuous wave device.A composite blood flow system incorporating all three Doppler techniques is described. Blood flow spectrograms from various sites within the pregnant uterus are presented