Table 1 - uploaded by Kerry Hourigan
Content may be subject to copyright.
Source publication
A novel Stereo PIV technique, with improvements over other techniques, is presented. The key feature of the new technique
is the direct measurement of calibration data at each point in space on the measurement grid, so that no interpolation is
necessary. This is achieved through the use of a contiguous target which can be analysed using standard PI...
Context in source publication
Similar publications
Taking self-propelled anti-aircraft gun as the research object, this paper presents a joint simulation method of shooting dynamics and servo control during the course of self-propelled anti-aircraft gun. Aiming at the matching between structural parameters and servo control parameters of self-propelled anti-aircraft gun, an evaluation and optimizat...
The velocity, coupling term in the flow and transport problems, is important in the accurate numerical simulation or in the posteriori error analysis for adaptive mesh refinement. We consider Enhanced Velocity Mixed Finite Element Method for the incompressible Darcy flow. In this paper, our aim to study the improvement of velocity at interface to a...
This paper presents a normalization-based approach to the mobility analysis of spatial compliant multi-beam modules to address the dimensional-inhomogeneity issue of motion/load. Firstly, two spatial non-tilted and tilted multi-beam modules, composed of uniform beams with symmetrical cross sections and same length, are proposed. Using a normalizati...
Citations
... The XV technology was originally developed in the mid-2000s from innovations in the fields of experimental fluid mechanics, image processing, x-ray physics [73][74][75][76] and in vivo x-ray imaging, 77,78 designed specifically for imaging of ventilation, 79-83 airway surfaces, [84][85][86] mucociliary transport [87][88][89] and blood flow. 90,91 Significant technical advancements that led to the derivation of XV technology were: (1) the ability to measure motion in three spatial dimensions using X-rays acquired at a single projection angle 92 ; (2) the ability to reconstruct, using multiple x-ray projections, a three-dimensional (3D) motion field without the need to reconstruct a 3D image of the structure 93,94 and (3) the ability to accurately and reliably calculate regional ventilation data from a 3D motion field. ...
In recent years, pulmonary imaging has seen enormous progress, with the introduction, validation and implementation of new hardware and software. There is a general trend from mere visual evaluation of radiological images to quantification of abnormalities and biomarkers, and assessment of 'non visual' markers that contribute to establishing diagnosis or prognosis. Important catalysts to these developments in thoracic imaging include new indications (like computed tomography [CT] lung cancer screening) and the COVID-19 pandemic. This review focuses on developments in CT, radiomics, artificial intelligence (AI) and x-ray velocimetry for imaging of the lungs. Recent developments in CT include the potential for ultra-low-dose CT imaging for lung nodules, and the advent of a new generation of CT systems based on photon-counting detector technology. Radiomics has demonstrated potential towards predictive and prognostic tasks particularly in lung cancer, previously not achievable by visual inspection by radiologists, exploiting high dimensional patterns (mostly texture related) on medical imaging data. Deep learning technology has revolutionized the field of AI and as a result, performance of AI algorithms is approaching human performance for an increasing number of specific tasks. X-ray velocimetry integrates x-ray (fluoroscopic) imaging with unique image processing to produce quantitative four dimensional measurement of lung tissue motion, and accurate calculations of lung ventilation.
... Here, the term "post-correction" refers to the correction of the misalignment error after obtaining the 3C-2D measurements, which were calibrated using the misaligned calibration target. The target-free calibration method proposed by Fouras et al. (2007), Fouras et al. (2008) suggests the elimination of the calibration target and the use of a third paraxial camera instead to compute the mapping functions of the two stereo cameras from their particle images cross-correlated with the simultaneously recorded particle images of the paraxial camera. While this method seems attractive when the placement of a calibration grid in the measurement region is not feasible, it requires an additional camera which adds to the cost and complexity of the experimental setup. ...
... Disparity map 0.50 SD Target-free calibration Fouras et al. (2007Fouras et al. ( , 2008 Calibration using cross-correlation of particle images of two stereo cameras with the particle images of a third paraxial camera 0.07 SD target and the photo-detectors used in the alignment process. The target frame has been designed and manufactured at the Laboratory for Turbulence Research in Aerospace and Combustion (LTRAC). ...
... The calibration is performed using the calibration images of the aligned calibration target. The 3C displacements reconstructed from the 2C displacements measured at the image planes of the two stereo cameras show a maximum uncertainty of less than 5.9 m (0.09 pixels) which compares favourably to the uncertainty of 4.0 m (0.06 pixels) of the self-calibration method (Wieneke 2005), as well as 7.0 m (0.07 pixels) of the target-free calibration method (Fouras et al. 2007(Fouras et al. , 2008. This is achieved without any ad hoc post-correction to the SPIV measurements, which demonstrates that the new method is an effective alternative to the post-correction schemes such as self-calibration and eliminates the risk of introducing a bias error into the PIV measurements. ...
The calibration of two-component–two-dimensional (2C-2D) particle image velocimetry (PIV) and three-component–two-dimensional (3C-2D) stereoscopic PIV (SPIV) systems generally requires a calibration target to be placed within the laser sheet that is parallel to it, covering the field of view. In practice, this is very difficult to achieve. Any misalignment between the calibration target and the laser sheet results in a position or velocity error. In 3C-2D SPIV, a number of methods use the disparity between the two cameras to estimate this misalignment. These techniques adjust the calibration or the 3C displacement field to reduce the error due to misalignment, but in doing so, they can introduce an unintended bias error in the measured 3C displacements. This paper introduces a novel method to ensure accurate parallel alignment of the laser sheet with the calibration target so that the error due to misalignment is minimized, if not completely avoided. The proposed method has been validated using two approaches: (i) by imaging the laser sheet and measuring the sheet rotation angle and (ii) using 3C-2D SPIV measurements of microparticles inside a block, which are illuminated using an aligned parallel laser sheet, while the block is translated by known displacements. This experiment demonstrates that the uncertainty in the 3C displacement is less than 5.9μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$5.9\,\mu$$\end{document}m (0.09 pixels), illustrating the usefulness of the new proposed alignment method for PIV calibration.
Graphic abstract
... A target free calibration method proposed by Fouras et al. [4] and further detailed in Fouras et al. [5] suggests the elimination of the calibration target and use of a third paraxial camera instead to compute mapping functions of each of the two stereo cameras from their particles images cross-correlated with the particle images of the paraxial camera, all recorded at the same time. While this method seems attractive when placement of a calibration grid in the measurement region is not feasible, it, however, needs an additional camera of the same spatial resolution as the other two and hence adds to the cost of the experimental setup. ...
Several calibration techniques have been proposed in the literature for the calibration of two-component two-dimensional (2C-2D) particle image velocimetry (PIV) and three-component two-dimensional (3C-2D) stereoscopic PIV (SPIV) systems. These techniques generally involve the use of a calibration target that is assumed to be at the exact centre of the laser sheet within the field of view (FOV), which in practice is very difficult to achieve. In 3C-2D SPIV, several methods offer different correction schemes based on the computation of a disparity map, which are aimed at correcting errors produced due to this misalignment. These techniques adjust the calibration of individual cameras to reduce the disparity error, but in doing so can create unintended errors in the measurement position and/or the velocity measurements, such as introducing a bias in the measured three-component (3-C) displacements. This paper introduces a novel method to ensure accurate alignment of the laser sheet with the calibration target so that the uncertainty in displacement measurements is less than or equal to the uncertainty inherent to the PIV and hence, no correction scheme is required. The proposed method has been validated with a simple experiment in which true displacements are given to a particle container (illuminated by an aligned laser sheet) and the measured 3C displacements are compared with the given true displacements. An uncertainty of less than 7.6 micrometres (equivalent to 0.114 pixels) in the measured 3C displacements demonstrates the effectiveness of the new alignment method and eliminates the need for any ad hoc post-correction scheme.
... SPIV utilizes two angled cameras and a single laser plane to measure threecomponent flow field velocities in a two-dimensional (2D) slice. Other techniques using three cameras have been developed to improve accuracy and improve calibration procedures [6,7]. While 3D measurement techniques, such as tomographic particle image velocimetry (PIV), have been shown to improve velocity estimates when studying fluid flows in a 3D area of interrogation, the additional equipment and computations are necessary to make these techniques less widely used for validation experiments [8]. ...
Two methods are investigated to simultaneously obtain both three-dimensional (3D) velocity field and free surface elevations (FSEs) measurements near a surface piercing foil, while limiting the equipment. The combined velocity field and FSE measurements are obtained specifically for the validation of numerical methods requiring simultaneous field data and free surface measurements for a slender body shape. Both methods use stereo particle image velocimetry (SPIV) to measure three component velocities in the flow field and both methods use an off the shelf digital camera with a laser intersection line to measure FSEs. The first method is performed using a vertical laser sheet oriented parallel to the foil chord line. Through repetition of experiments with repositioning of the laser, a statistical representation of the three-dimensional flow field and surface elevations is obtained. The second method orients the vertical laser sheet such that the foil chord line is orthogonal to the laser sheet. A single experiment is performed with this method to measure the three-dimensional three component (3D3C) flow field and free surface, assuming steady flow conditions, such that the time dimension is used to expand the flow field in 3D space. The two methods are compared using dynamic mode decomposition and found to be comparable in the primary mode. Utilizing these methods produces results that are acceptable for use in numerical methods verification, at a fraction of the capital and computing cost associated with two plane or tomographic particle image velocimetry (PIV).
... Velocity measurements in this study were performed using an in-house code [17] that has been thoroughly validated [18] and shown to measure motion accurately to 0.03px [17,19]. Red blood cells were utilised to act as the tracer particles, as has been performed by previous studies [4,11,12,20]. ...
Physical forces can influence the embryonic development of many tissues. Within the cardiovascular system shear forces resulting from blood flow are known to be one of the regulatory signals that shape the developing heart. A key challenge in investigating the role of shear forces in cardiac development is the ability to obtain shear force measurements in vivo. Utilising the zebrafish model system we have developed a methodology that allows the shear force within the developing embryonic heart to be determined. Accurate wall shear measurement requires two essential pieces of information; high-resolution velocity measurements near the heart wall and the location and orientation of the heart wall itself. We have applied high-speed brightfield imaging to capture time-lapse series of blood flow within the beating heart between 3 and 6 days post-fertilization. Cardiac-phase filtering is applied to these time-lapse images to remove the heart wall and other slow moving structures leaving only the red blood cell movement. Using particle image velocimetry to calculate the velocity of red blood cells in different regions within the heart, and using the signal-to-noise ratio of the cardiac-phase filtered images to determine the boundary of blood flow, and therefore the position of the heart wall, we have been able to generate the necessary information to measure wall shear in vivo. We describe the methodology required to measure shear in vivo and the application of this technique to the developing zebrafish heart. We identify a reduction in shear at the ventricular-bulbar valve between 3 and 6 days post-fertilization and demonstrate that the shear environment of the ventricle during systole is constantly developing towards a more uniform level.
... In this traditional form, the method provides no out-of-plane flow information. The most common solution to overcome this is stereoscopic PIV [13], [14], [15]; with two cameras, the local out-of-plane velocity may be calculated. Unfortunately, as laser sheet is the main light source, only a plane of velocity field could be measured at a time. ...
We describe a method for measuring three dimensional (3D) velocity fields of a fluid at high speed, by combining a correlation-based approach with in-line holography. While this method utilizes tracer particles contained within the flow, our method does not require the holographic reconstruction of 3D images. The direct flow reconstruction approach developed here allows for measurements at seeding densities in excess of the allowable levels for techniques based on image or particle reconstruction, thus making it suited for biological flow measurement, such as the flow in bioreactor. We outline the theory behind our method, which we term Holographic Correlation Velocimetry (HCV), and subsequently apply it to both synthetic and laboratory data. Moreover, because the system is based on in-line holography, it is very efficient with regard to the use of light, as it does not rely on side scattering. This efficiency could be utilized to create a very high quality system at a modest cost. Alternatively, this efficiency makes the system appropriate for high-speed flows and low exposure times, which is essential for imaging dynamic systems.
... This code has been developed over a number of years and has been rigorously validated (Fouras et al., 2009b;Nesbitt et al., 2009). The uncertainty of displacements measured using this code has been found to be as low as 0.05 pixels (Fouras et al., 2007b). Whole-field velocity measurements were carried out on the blood flow through the excised vessel after performing the above-mentioned filtering. ...
X-ray velocimetry offers a non-invasive method by which blood flow, blood velocity and wall shear stress can be measured in arteries prone to atherosclerosis. Analytical tools for measuring haemodynamics in artificial arteries have previously been developed and here the first quantification of haemodynamics using X-ray velocimetry in a living mammalian artery under physiologically relevant conditions is demonstrated. Whole blood seeded with a clinically used ultrasound contrast agent was pumped with a steady flow through live carotid arterial tissue from a rat, which was kept alive in a physiological salt solution. Pharmacological agents were then used to produce vascular relaxation. Velocity measurements were acquired with a spatial resolution of 14 µm × 14 µm and at a rate of 5000 acquisitions per second. Subtle velocity changes that occur are readily measurable, demonstrating the ability of X-ray velocimetry to sensitively and accurately measure haemodynamics ex vivo. Future applications and possible limitations of the technique are discussed, which allows for detailed living tissue investigations to be carried out for various disease models, including atherosclerosis and diabetic vasculopathy.
... To determine any motion of the animal as a whole a crosscorrelation analysis was performed using large interrogation windows that included the bone structure of the animal; this was subtracted from the motion of the lungs. The X-ray velocimetry measurements were performed using in-house software as used in [52] and as described in detail in [57] with a detailed error analysis in [58]. The cross-correlation utilised an interrogation window size of 64664 pixels and 75% window overlap. ...
Although high frequency ventilation (HFV) is an effective mode of ventilation, there is limited information available in regard to lung dynamics during HFV. To improve the knowledge of lung function during HFV we have developed a novel lung imaging and analysis technique. The technique can determine complex lung motion information in vivo with a temporal resolution capable of observing HFV dynamics. Using high-speed synchrotron based phase contrast X-ray imaging and cross-correlation analysis, this method is capable of recording data in more than 60 independent regions across a preterm rabbit lung in excess of 300 frames per second (fps). This technique is utilised to determine regional intra-breath lung mechanics of preterm rabbit pups during HFV. Whilst ventilated at fixed pressures, each animal was ventilated at frequencies of 1, 3, 5 and 10 Hz. A 50% decrease in delivered tidal volume was measured at 10 Hz compared to 1 Hz, yet at the higher frequency a 500% increase in minute activity was measured. Additionally, HFV induced greater homogeneity of lung expansion activity suggesting this ventilation strategy potentially minimizes tissue damage and improves gas mixing. The development of this technique permits greater insight and further research into lung mechanics and may have implications for the improvement of ventilation strategies used to support severe pulmonary trauma and disease.
... Hence, this method allows stereoscopic PIV measurements to be taken inside closed measurement volumes (Wieneke, 2005). Fouras et al. (2007Fouras et al. ( , 2008) developed a novel, accurate, and simple calibration-targetfree stereoscopic PIV technique utilizing three cameras. The key feature of this technique is that there is no need of a separate calibration phase but utilizes a third camera placed in paraxial (normal to the laser light sheet) position. ...
... The key feature of this technique is that there is no need of a separate calibration phase but utilizes a third camera placed in paraxial (normal to the laser light sheet) position. This calibration-target-free technique offers the advantages of the calibration-target-based stereoscopic PIV, with even greater improvements in reconstruction accuracy and without the requirement of the practitioner to conduct a distinct calibration phase, and is greatest utility when the paraxial view has minimal distortion or when it is not convenient to place a calibration target in the measurement region (Fouras et al., 2007(Fouras et al., , 2008. ...
Many cells are considered to be susceptible to mechanical forces or “shear” in bioprocessing, leading to undesirable cell breakage or adverse metabolic effects. However, cell breakage is the aim of some processing operations, in particular high-pressure homogenisation and other cell disruption methods. In either case, the exact mechanisms of damage or disruption are obscure. One reason for this is that the mechanical properties of the cells are generally unknown, which makes investigation or prediction of the damage difficult. There are several methods for measuring the mechanical properties of single microbial cells, and these are reviewed briefly. In the context of bioprocessing research, a powerful method of characterising the mechanical properties of single cells is compression testing using micromanipulation, supplemented by mathematical modelling of the cell behaviour in compression. The method and associated modelling are described, with results mainly from studies on yeast cells. Continuing difficulties in making a priori predictions of cell breakage in processing are identified. In future, compression testing by micromanipulation might also be used in conjunction with other single cell analytical techniques to study mechanisms controlling form, growth and division of cells and their consequential mechanical behaviour. It ought to be possible to relate cell wall mechanics to cell wall composition and structure, and eventually to underlying gene expression, allowing much greater understanding and control of the cell mechanical properties.
Graphical Abstract
Typical fit of model to force-deformation data from compression of a single Saccharomyces cerevisiae cell by micromanipulation
... Hence, this method allows stereoscopic PIV measurements to be taken inside closed measurement volumes (Wieneke, 2005). Fouras et al. (2007Fouras et al. ( , 2008) developed a novel, accurate, and simple calibration-targetfree stereoscopic PIV technique utilizing three cameras. The key feature of this technique is that there is no need of a separate calibration phase but utilizes a third camera placed in paraxial (normal to the laser light sheet) position. ...
... The key feature of this technique is that there is no need of a separate calibration phase but utilizes a third camera placed in paraxial (normal to the laser light sheet) position. This calibration-target-free technique offers the advantages of the calibration-target-based stereoscopic PIV, with even greater improvements in reconstruction accuracy and without the requirement of the practitioner to conduct a distinct calibration phase, and is greatest utility when the paraxial view has minimal distortion or when it is not convenient to place a calibration target in the measurement region (Fouras et al., 2007(Fouras et al., , 2008. ...
This chapter is devoted to the methodology of particle image velocimetry (PIV) techniques and its applications to multiphase flow systems. It reviews, first, the fundamental issues of a conventional PIV with considerations of improvements of spatial resolution and accuracy; second, the state of the art in various types of PIV techniques from the viewpoint of dimensions and velocity components of the measurement, the flow passage scales, and the hardware components of the system; third, the state of the art in some issues about the measurement of multiphase flow systems using PIV techniques. The multiphase flows to which the applications of PIV techniques are discussed include liquid–liquid two fluid flows, gas–liquid two-phase flows, and particle-laden multiphase flow systems.The emphasis in this chapter is on the fruitful methodology of PIV techniques that emerge in the recent publications instead of the detailed discussions on any individual research topic of the measurement target of PIV. The purpose is to provide an overall instructive introduction and guidance to the PIV techniques and its applications particularly in the research field of multiphase flows. To this end, fruitful examples of PIV measurements of free-surface liquid flows, bubbly flows, particle-laden multiphase flows, etc., are elucidated.
