Abstract: This study is the analysis and design of a basin structure which has the ability to form a gravitational vortex stream. Such a high velocity water vortex stream can possibly be used as an alternative energy resource. In this study we are interested in the formation of a water vortex stream by gravitation, which is a new technique used in the field of hydro power engineering. The advantage of this method for electrical generation is the capability of producing energy using low heads of 0.7 to 3 meters. It can be applied in a low head micro hydro power plant. The governing equations are the Navier-Stokes equations. The SIMPLE method was adopted to solve the discretized equation. The flow fields in the flume, under different incoming flow conditions and basin configurations, were numerically simulated using the software ANSYS Fluent. The studies investigated parameters which affect the velocity vector flow field, which include 1) Outlet diameter at the bottom center of basin 2) Gravitational vortex head and 3) Flow rate. Computational fluid dynamics is used to simulate the vector flow field. The tangential and radial velocity distribution is used to determine the suitable turbine blade for testing. A gravitational vortex power plant model is created to investigate electrical power output.

Abstract: In evaluating the cardiac function, it is important to have a comprehensive assessment of structural factors, such as the myocardial or valvular function and intracardiac flow dynamics that pass the heart. Vortex flow that form during left ventricular filling have specific geometry and anatomical location that are critical determinants of directed blood flow during ejection. The formation of abnormal vortices relates to the abnormal cardiac function. Therefore, vortex flow may offer a novel index of cardiac dysfunction. Intracardiac flow visualization using ultrasound technique has definite advantages with a higher temporal resolution and availability in real time clinical setting. Vector flow mapping based on color-Doppler and contrast echocardiography using particle image velocimetry is currently being used for visualizing the intracardiac flow. The purpose of this review is to provide readers with an update on the current method for analyzing intracardiac flow using echocardiography and its clinical applications.

Abstract: Techniques are provided to improve the performance and accuracy of landmark point detection using a Constrained Local Model. The accuracy of feature filters used by the model may be improved by supplying positive and negative sets of image data from training image regions of varying shapes and sizes to a linear support vector machine training algorithm. The size and shape of regions within which a feature filter is to be applied may be determined based on a variance in training image data for a landmark point with which the feature filter is associated. A sample image may be normalized and a confidence map generated for each landmark point by applying the feature filters as a convolution on the normalized image. A vector flow map may be pre-computed to improve the efficiency with which a mean landmark point is adjusted toward a corresponding landmark point in a sample image.

Abstract: A method for making Vector Flow Images using the transverse oscillation (TO) approach on a convex array is presented. The paper presents optimization schemes for TO fields for convex probes and evaluates their performance using Field II simulations and measurements using the SARUS experimental scanner. A 3 MHz 192 elements convex array probe (pitch 0.33 mm) is used in both simulations and measurements. An F-number of 5 is used in transmit and two 32 element wide peaks are used in receive separated by 96 elements between peaks. Parabolic velocity profiles are simulated at beam-to-flow angles from 90 to 45 degrees in steps of 15 degrees. The optimization routine changes the lateral oscillation period λx to yield the best possible estimates based on the energy ratio between positive and negative spatial frequencies in the ultrasound field. The basic equation for λx gives 1.14 mm at 40 mm, and 1.51 mm from the simulated point spread function. This results in a bias of 35% as λx directly scales the estimated velocities. Optimizing the focusing yields a λx of 1.61 mm. The energy ratio is reduced from -12.8 dB to -20.1 dB and the spectral bandwidth from 115.1 m-1 to 96.5 m-1. λx is maintained between 1.47 and 1.70 mm from 25 mm to 70 mm and is increased to 2.8 mm at a depth of 100 mm. Parabolic profiles are estimated using 16 emissions. The optimization gives a reduction in std. from 8.5% to 5.9% with a reduction in bias from 35% to 1.02% at 90 degrees (transverse flow) at a depth of 40 mm. Measurements have been made using the SARUS experimental ultrasound scanner and a BK Medical 8820e convex array transducer. Sixty-four elements was used in transmit and 2 × 32 elements in receive for creating a color flow map image of a flow rig phantom with a laminar, parabolic flow. At 75 degrees a bias of less than 1% was obtained.

Abstract: In this work, we present an automatic segmentation of the left atrium on computed tomography imaging CT. The left atrium has an important role in patients with ventricular dysfunction as a booster pump to augment ventricular volume. A method based on active contours models with gradient vector flow is proposed in this paper and applied for left atrium segmentation. At first, a contrast enhancement is applied to improve the image quality. The automated initialization method is followed by a region-growing technique for a preliminary segmentation. The result of this technique is used as initialization for a segmentation method using a Gradient Vector Flow GVF snake based approach. The initial model can hence be attracted to the borders of the left atrium following various internal and external forces including the gradient vector flow GVF.

Abstract: An ultrasound imaging system includes a vector flow imaging processor that processes ultrasound data representing structure flowing through a tubular object and generates vector flow imaging information for a region of interest of the tubular object that is indicative of the structure flowing through a tubular object based thereon and processing circuitry that determines at least one parameter for Doppler imaging based on the vector flow imaging information.

Abstract: In this paper, we propose a fast centerline extraction method to be used for gradient and direction vector flow of active contours. The gradient and direction vector flow is a recently reported active contour model capable of significantly improving the image segmentation performance especially for complex object shape, by seamlessly integrating gradient vector flow and prior directional information. Since the prior directional information is provided by manual line drawing, it can be inconvenient for inexperienced users who might have difficulty in finding the best place to draw the directional lines to achieve the best segmentation performance. This paper describes a method to overcome this problem by automatically extracting centerlines to guide the users for providing the right directional information. Experimental results on synthetic and real images demonstrate the feasibility of the proposed method.

Abstract: In this paper we propose a novel approach to the extraction of medial axis for grayscale objects. The method utilizes a computationally efficient vector field convolution to enhance the medialness feature. Local maxima of medialness are analyzed in scale space, yielding a robust medial axis for grayscale imagery. An important application of this work is the segmentation of neurons from noisy, cluttered microscopy images. Existing neuron segmentation methods depend heavily on accurate, noise-insensitive medial axis extraction. We propose the vector field convolution medialness operation as a first step in segmenting neurons. The proposed method requires no complex parameters or an initial binarization step. The efficacy of the method is demonstrated by a 60% reduction root mean squared error (2.9 pixels) as compared to an approach based on gradient vector flow.

Abstract: Conventional ultrasound flow imaging systems are limited to estimate only the axial component of blood velocity. In this work, a method to produce 2D vector Doppler maps is proposed and experimentally tested. The local displacements between consecutive high frame-rate (HFR) radio-frequency (RF) images are estimated in the frequency domain. Each image is subdivided in partially overlapped matching blocks, and the average local displacements in a block are calculated from the difference of spectral phases in consecutive frames. The method has been tested by simulations and experiments by using the ULA-OP research scanner. Preliminary in-vivo tests have been conducted and an example of the femoral vessels of a healthy volunteer is presented. The performance of the method are evaluated through the relative error bias and standard deviation, presenting values lower than 10% in standard conditions.

Abstract: This paper presents a novel energy back-projective composition model (EBPCM) for 3-D reconstruction of the coronary arteries from two mono-plane angiographic images. A major problem with the commonly used parameter deformable model is that the predefined correspondences may become non-strict matching after the curve evolution, which generally leads to large extra calculation errors. In this study, the energy field in the image is back-projected to 3-D space and decomposed into three independent components in the world coordinates centered at the iso-center of the C-arm. Then, the components from different views are composited together according to the rotation and scaling relationship of the imaging angles. The composited energy field hence is utilized as the external force to control the evolution of the vascular structure in 3-D space. As the driving force is iteratively updated according to energy in the two projection images, the non-strict matching can be effectively avoided. Also, the proposed method is very flexible, which can be composited with any energy fields such as Generalized Gradient Vector Flow (GGVF) and Potential Energy (PE) etc. Experiments demonstrate that the proposed method is very effective and robust, when using GGVF as the external force, the reconstruction RMS error can be reduced to about 0.595mm in the 3-D space.

Abstract: An ultrasound imaging system (100) includes a velocity processor (118) that processes ultrasound data representing structure flowing through a tubular object and generates vector flow imaging information indicative of the structure flowing through a tubular object based thereon. The vector flow imaging information includes an axial velocity component signal and a lateral component signal, and the axial and lateral component signals indicate a direction and a speed of the structure flowing through the tubular object. The ultrasound imaging system further includes a flow parameter processor (120) that determines at least one flow parameter based on the vector flow imaging information and generates a signal indicative thereof.

Abstract: Evaluation of right ventricular (RV) structure and function is of importance in the management of most cardiac disorders. But the segmentation of RV has always been considered challenging due to low contrast of the myocardium with surrounding and high shape variability of the RV. In this paper, we present a 2D + T active contour model for segmentation and tracking of RV endocardium on cardiac magnetic resonance (MR) images. To take into account the temporal information between adjacent frames, we propose to integrate the time-dependent constraints into the energy functional of the classical gradient vector flow (GVF). As a result, the prior motion knowledge of RV is introduced in the deformation process through the time-dependent constraints in the proposed GVF-T model. A weighting parameter is introduced to adjust the weight of the temporal information against the image data itself. The additional external edge forces retrieved from the temporal constraints may be useful for the RV segmentation, such that lead to a better segmentation performance. The effectiveness of the proposed approach is supported by experimental results on synthetic and cardiac MR images.

Abstract: Active contour models are used to extract object boundary from digital image, but there is poor convergence for the targets with deep concavities. We proposed an improved approach based on existing gradient vector flow methods. Main contributions of this paper are a new algorithm to determine the false part of active contour with higher accuracy from the global force of gradient vector flow and a new algorithm to update the external force field together with the local information of magnetostatic force. Our method has a semidynamic external force field, which is adjusted only when the false active contour exists. Thus, active contours have more chances to approximate the complex boundary, while the computational cost is limited effectively. The new algorithm is tested on irregular shapes and then on real images such as MRI and ultrasound medical data. Experimental results illustrate the efficiency of our method, and the computational complexity is also analyzed.

Abstract: Conventional color flow images are limited in velocity range and can either show the high velocities in systole or be optimized for the lower diastolic velocities. The full dynamics of the flow is, thus, hard to visualize. The dynamic range can be significantly increased by employing synthetic aperture flow imaging as demonstrated in this paper. Synthetic aperture, directional beamforming, and cross-correlation are used to produce B-mode and vector velocity images at high frame rates. The frame rate equals the effective pulse repetition frequency of each imaging mode. Emissions for making the B-mode images and velocity maps are interleaved in a 1-to-1 ratio. This provides continuous data allowing a wide range of velocities to be estimated. Two cases are considered in the flow estimation: In the first case, the angle of the flow is determined from the B-mode image. In the other case, the angle is determined by estimating the flow velocity in all directions and choosing the one with the strongest correlation. The method works for all angles, including fully axial and fully transverse flows. Field II simulations with a 192 element, 7 MHz linear array are made of laminar, transverse flow profiles. For a simulated peak velocity of 0.5 m/s, the relative bias is -6.8% and the relative standard deviation is 6.1%. The bias on the angle is 0.98 degrees with a standard deviation of 2.39 degrees when using the flow estimator to determine the angle. For a peak velocity of 0.05 m/s, the relative bias of the velocity estimation is -1.8% and the relative standard deviation 5.4%. The approach can thus estimate both high and low velocities with equal accuracy and thereby makes it possible to present vector flow images with a high dynamic range. Measurements are made using the SARUS research scanner, a linear array transducer similar to the simulated one, and a recirculating flow rig with a blood mimicking fluid and a parabolic flow profile with a peak velocity of approximately 0.3 m/s. The relative bias of the velocity estimation is 0.19% and the mean relative standard deviation 4.9%. For the direction estimation, the bias is 3.2 degrees with a standard deviation of 1.6 degrees.

Abstract: Active contour model combined with traditional edge detection can be used to extract land-sea boundary,but it is sensitive to shortcomings of boundary tracing.Based on the traditional method,edge detection and the directed force of gradient vector flow are used to generate the initial contour,then the active contour model is used to adjust the initial contour to the actual boundary precisely.According to the experiments,the new method can generate the initial contour simply and extract land-sea boundary accurately without boundary tracing.What's more,the new method can be used to simplify the extraction process with GIS(Geographic Information System)assistance.

Abstract: The recently proposed Neighborhood-extending and Noise-smoothing Gradient Vector Flow (NNGVF) provides a better segmentation to images than the GVF in terms of noise resistance, weak edges preservation. However, the NNGVF snake still has difficulties converging into long, thin boundary indentations. In this paper, we propose a novel external force for active contour models named NNGGVF which is a generalization of the NNGVF include two spatially varying weighting functions. It improves snake's ability of convergence into long, thin boundary indentations while maintaining other desirable properties of the NNGVF, such as better noise immunity and enlarged capture range. We demonstrate the advantages of the NNGGVF on synthetic and real images.

Abstract: We proposed a motion segmentation method a few months ago. The problem of it is that the contour of the object segmented from the image sequence is always unclosed. This paper presents a method of the Gradient Vector Flow (GVF) field snake to close the contour. The initial curve of the GVF snake is rectangle, so that the curve can be used in the tracking and recognition applications. However, corners of initial curve are always located out of the GVF field. In order to evolve the initial curve correctly, a hybrid field snake method is proposed to solve this problem. In the final part of this paper, we give some experiments to test our method, and the result is satisfactory.

Abstract: The microvasculature network of retina plays an important role in the study and diagnosis of retinal diseases (age-related macular degeneration and diabetic retinopathy for example). Although it is possible to noninvasively acquire high-resolution retinal images with modern retinal imaging technologies, non-uniform illumination, the low contrast of thin vessels and the background noises all make it difficult for diagnosis. In this paper, we introduce a novel retinal vessel extraction algorithm based on gradient vector flow and matched filtering to segment retinal vessels with different likelihood. Firstly, we use isotropic Gaussian kernel and adaptive histogram equalization to smooth and enhance the retinal images respectively. Secondly, a multi-scale matched filtering method is adopted to extract the retinal vessels. Then, the gradient vector flow algorithm is introduced to locate the edge of the retinal vessels. Finally, we combine the results of matched filtering method and gradient vector flow algorithm to extract the vessels at different likelihood levels. The experiments demonstrate that our algorithm is efficient and the intensities of vessel images exactly represent the likelihood of the vessels.

Abstract: We try in this work to solve the problem of automatic detection of contours of circular geologic structures of the Adrar Tikertine (feuille de Tinfelki) on radar remote sensing images. The utility of these structures is irrefutable, particularly in mineral prospecting and geological cartography. To reach this goal, we use an active contour model called Gradient Vector Flow (GVF). With the difference to traditional approaches, the Gradient Vector Flow (GVF) concept includes simultaneously two operations: detection and edge link of contour points. The last one was always considered as a very complicated task in traditional approaches and must be done separately from detection of contour points. In fact, the strong point of the GVF active contours is the definition of new external force able to attract the deformable contour to concave regions, generally not attained with traditional active contours called “snakes”.

Abstract: Flow fields produced by physically based simulations are subsets of multivariate spatiotemporal data, and have been in interest of many researchers for visualization, since the data complexity makes it difficult to extract representative views for the interpretation of fluid behavior. In this thesis, we utilize Information Theory to find entropy maps for vector flow fields, and use entropy maps to aid visualization and analysis of the flow fields. Our major contribution is to use Principal Component Analyses (PCA) to find a projection that has the maximal directional variation in polar coordinates for each sampling window in order to generate histograms according to the projected 3D vector field, producing results with fewer artifacts than the traditional methods. Entropy guided visualization of different data sets are presented to evaluate proposed method for the generation of entropy maps. High entropy regions and coherent directional components of the flow fields are visible without cluttering to reveal fluid behavior in rendered images. In addition to using data sets those are available for research purposes, we have developed a fluid simulation framework using Smoothed Particle Hydrodynamics (SPH) to produce flow fields. SPH is a widely used method for fluid simulations, and used to generate data sets that are difficult to interpret with direct visualization techniques. A moderate improvement for the performance and stability of SPH implementations is also proposed with the use of fractional derivatives, which are known to be useful for approximating particle behavior immersed in fluids.

Abstract: The cardiac flow is complex and multidirectional, and difficult to measure with conventional Doppler ultrasound (US) methods due to the one-dimensional and angle-dependent velocity estimation. The vector velocity method Transverse Oscillation (TO) has been proposed as a solution to this. TO is implemented on a conventional US scanner (Pro Focus 2202 UltraView, BK Medical) using a linear transducer (8670, BK Medical) and can provide real-time, angle-independent vector velocity estimates of the cardiac blood flow. During cardiac surgery, epicardiac US examinations using TO were performed on three patients. Antegrade central jet and retrograde flow near the vessel wall in the ascending aorta and the pulmonary artery were seen during systole, while stable vortices were seen in the aortic sinuses and complex flow patterns were seen around the valves during diastole. In the right atrium, a stable vortex was seen during the entire heart cycle. For comparison, simultaneous measurements were obtained with conventional spectral Doppler (SD) and intravenous catheter thermodilution technique (TD). Peak systolic velocities were underestimated by 18% compared to SD and cardiac output was underestimated by 16% compared to TD. This is the first time TO measurements have been obtained of cardiac flow. TO can potentially reveal new information of cardiovascular physiology and blood flow dynamics, and become a valuable tool in cardiology.