Centerline Model Research Articles

Development of the pulmonary vasculature in the gray short-tailed opossum (Monodelphis domestica)-3D reconstruction by microcomputed tomography.

In the marsupial gray short-tailed opossum (Monodelphis domestica), the majority of lung development, including the maturation of pulmonary vasculature, takes place in ventilated functioning state during the postnatal period. The current study uses X-ray computed tomography (μCT) to three-dimensionally reconstruct the vascular trees of the pulmonary artery and pulmonary vein in 15 animals from neonate to postnatal day 57. The final 3D reconstructions of the pulmonary artery and pulmonary vein in the neonate and at 21, 35, and 57 dpn were transformed into a centerline model of the vascular trees. Based on the reconstructions, the generation of end-branching vessels, the median and maximum generation, and the number of vessels were calculated for the lungs. The pulmonary vasculature follows the lung anatomy with six pulmonary lobes indicated by the bronchial tree. The pulmonary arteries follow the bronchial tree closely, in contrast to the pulmonary veins, which run between the pulmonary segments. At birth the pulmonary vasculature has a simple branching pattern with a few vessel generations. Compared with the bronchial tree, the pulmonary vasculature appears to be more developed and extends to the large terminal air spaces. The pulmonary vasculature shows a marked gain in volume and a progressive increase in vascular complexity and density. The gray short-tailed opossum resembles the assumed mammalian ancestor and is suitable to inform on the evolution of the mammalian lung. Vascular genesis in the marsupial bears resemblance to developmental patterns described in eutherians. Lung development in general seems to be highly conservative within mammalian evolution.

The Chevron Effect: Reserve Strength of Existing Chevron Frames

Recently an analysis model has been developed to address the large shear forces (the so-called “chevron effect”) that can develop in the connection regions of chevron-braced frames. These shear forces (and the corresponding moments) are the result of the application of the brace forces at the beam flange, eccentric to the beam centerline. Prior to the presentation of these methods, such forces were not generally considered in design, without apparent incident. Sabelli and Saxey presented an alternative model that determines substantially higher resistance in these connections. Both models resolve the shear and moment within the connection region such that forces outside that region are consistent with those determined using a centerline model. Greater resistance can be determined if the flexural strength of braces and the beam outside the connection region are used to resist a portion of the chevron moment. This paper presents a complete plastic-mechanism strength of the chevron frame with yielding of the beam web due to the local shear forces. This complete plastic mechanism strength can confirm the adequacy of existing designs that did not consider the chevron effect.

Short-Term Lateral Behavior Reasoning for Target Vehicles Considering Driver Preview Characteristic

A timely understanding of target vehicles (TVs) lateral behavior is essential for the decision-making and control of host vehicle. Existing physical model-based methods such as motion-based method and multiple centerline-based method are generally constructed based on TV pose and longitudinal velocity, and tend to ignore TV preview driving characteristic and other useful information such as lateral velocity and yaw rate. To address these issues, a driver preview and multiple centerline model-based probabilistic behavior recognition architecture is proposed for timely and accurate TV lateral behavior prediction. Firstly, a driver preview model is used to describe vehicle preview driving characteristic, and TV preview lateral offset and preview lateral velocity are calculated with TV states and road reference information. Then, the preview lateral offset and preview lateral velocity are combined with multiple centerline model for TV lateral behavior reasoning based on the interacting multiple model-based probabilistic behavior recognition algorithm. With this method, TV preview driving characteristic and lateral motion states are combined for precise TV lateral behavior description. Furthermore, to predict short-term lateral behavior, a preview lateral velocity-dependent transition probability matrix model constructed with Gaussian cumulative distribution function is proposed. Simulation and experimental results show that the proposed method considering vehicle preview driving characteristic predicts TV lateral behavior earlier than the conventional method.

A virtual reality based surgical skills training simulator for catheter ablation with real-time and robust interaction

BackgroundAtrial fibrillation (AF) is the most common sustained cardiac arrhythmia that can cause severe heart problems. Catheter ablation is one of the most ideal procedures for the treatment of AF. Physicians qualified to perform this procedure need to be highly skilled in manipulating the relevant surgical devices. This study proposes an interactive surgical simulator with high fidelity to facilitate efficient training and low-cost medical education. MethodsWe used a shared centerline model to simulate the interaction between multiple surgical devices. An improved adaptive deviation-feedback approach is proposed to accelerate the convergence of each iteration. The periodical beating of the human heart was also simulated in real time using the position-based dynamics (PBD) framework to achieve higher fidelity. We then present a novel method for handling the interaction between the devices and the beating heart mesh model. Experiments were conducted in a homemade simulator prototype to evaluate the robustness, performance, and flexibility of the proposed method. Preliminary evaluation of the simulator was performed by medical students, residents, and surgeons. ResultsThe interaction between surgical devices, static vascular meshes, and beating heart mesh was stably simulated in a frame rate suitable for interaction. ConclusionOur simulator is capable of simulating the procedure of catheter ablation with high fidelity and provides immersive visual experiences and haptic feedback.

Multiscale Feature‐feature Interactions Control Patterns of Hyporheic Exchange in a Simulated Headwater Mountain Stream

AbstractRecent predictions of hyporheic exchange at the basin‐scale assume individual features control exchange independently of each other, which has been demonstrated in relatively uniform, low‐gradient rivers. However, this assumption may not hold in steep catchments where both the type and size of individual features may vary over short distances, leading to irregular patterns of feature dominance on hyporheic exchange flows. Also, steep longitudinal gradients support substantial downvalley flows in the subsurface, which may create feedbacks between adjacent features. In this study, we test the extent to which features interact with one another and whether they can be aggregated to make reach‐scale predictions in a headwater mountain stream. Using systematic manipulations of a 2‐D stream centerline model and spectral analyses, we test for the presence of both feature‐feature and multiscale interactions. Our results show that changing the height of individual step‐pool features can alter hyporheic flow fields in neighboring, and sometimes distant, features. Spectral analyses revealed two scales of streambed topography—a local scale of single features and an intermediate scale that spanned multiple local‐scale features. All features produced hyporheic exchange, but turnover of deeper hyporheic water only occurred at a few key locations where local‐ and intermediate‐scale features amplified each other. Further, shallow bedrock increases the ratio of local‐ and intermediate‐scale flowpaths to regional‐scale flowpaths. Conceptual models portraying hyporheic exchange as a series of nested flowpaths should include the interactions among streambed topographic features in mountain streams. These results have implications for upscaling, field experiments, and stream restoration in steep catchments.

A Bifurcated Vascular Channel Construction Method based on Diploic Vein Characteristics

In skull bone tissue engineering, cells do not easily survive and proliferate in the scaffold because of the lack of nutrient transport channels. To address these problems, a vascular design and fabrication method based on human skull diploic vein characteristics was proposed. The skull sample was scanned by micro-CT, and the 3D model was constructed by Avizo. By analyzing the characteristics of the diploic vein, the vascular centerline model, path model, taper model and bifurcation model were proposed. Two vascular network examples were constructed by iteration of the bifurcation unit. The mold method of constructing vascular scaffolds embedded within the bionic channels was proposed. The scaffold material is PDMS, and the surface was coated with collagen. The Human Umbilical Vein Endothelial Cells (HUVECs) were planted into the lumen of the channels for 7 days in vitro and found to be able to proliferate. The cells cultured for three days were fluorescently stained, and it was found that the cells were well attached to the surfaces of the lumen. This vascular design and fabrication process can lay a foundation for vascularization in bone tissue engineering.

An adaptive deviation-feedback approach for simulating multiple devices interaction in virtual interventional radiology

Endovascular intervention is widely used in the treatment of cardiovascular and cerebrovascular diseases. This procedure requires physicians to be highly skilled at manipulating surgical devices such as catheters and guidewires. Virtual reality-based interventional simulators for surgical skills training have many advantages over traditional training methods. Simulation of the behavior of interventional devices is a very challenging task when developing such a simulator. In this paper, we proposed a shared centerline model incorporated with weighted material properties to represent the interventional devices. To efficiently and stably simulate the interactive behavior of these devices, we proposed an adaptive deviation-feedback approach to accelerate the convergence of the iterations. Additionally we proposed a track based control strategy to predict the behavior of the devices based on their past track to further decrease the amount of computation needed for the achievement of new equilibrium. The performance of our approach is experimentally validated via two endovascular interventional applications.

Conditioning 3D object-based models to dense well data

Object-based stochastic simulation models are used to generate categorical variable models with a realistic representation of complicated reservoir heterogeneity. A limitation of object-based modeling is the difficulty of conditioning to dense data. One method to achieve data conditioning is to apply optimization techniques. Optimization algorithms can utilize an objective function measuring the conditioning level of each object while also considering the geological realism of the object. Here, an objective function is optimized with implicit filtering which considers constraints on object parameters. Thousands of objects conditioned to data are generated and stored in a database. A set of objects are selected with linear integer programming to generate the final realization and honor all well data, proportions and other desirable geological features.Although any parameterizable object can be considered, objects from fluvial reservoirs are used to illustrate the ability to simultaneously condition multiple types of geologic features. Channels, levees, crevasse splays and oxbow lakes are parameterized based on location, path, orientation and profile shapes. Functions mimicking natural river sinuosity are used for the centerline model. Channel stacking pattern constraints are also included to enhance the geological realism of object interactions. Spatial layout correlations between different types of objects are modeled.Three case studies demonstrate the flexibility of the proposed optimization-simulation method. These examples include multiple channels with high sinuosity, as well as fragmented channels affected by limited preservation. In all cases the proposed method reproduces input parameters for the object geometries and matches the dense well constraints. The proposed methodology expands the applicability of object-based simulation to complex and heterogeneous geological environments with dense sampling.

Research on automatic coronary artery extraction algorithm based on CTA image and model guidance

When doctors diagnose coronary artery by CTA data, they need to look at each section layer by layer, which consumes a lot of diagnostic time. Introducing artificial intelligence technology, using CTA image computer-aided technology to extract coronary artery automatically or semi-automatically, and assisting analysis of coronary artery, can improve the efficiency of doctors, quickly make diagnosis of patients. A priori model of coronary artery centerline based on image registration is studied. A single priori model is formed by fusing multiple cardiac CTA data, which increases the generalization ability of the model and provides more accurate priori position information of main branches for unknown CTA data. According to the composition of the model, it will be divided into two parts: the cardiac cavity model and the centerline model. The implementation of the model establishment, DMP centerline extraction and coronary analysis is introduced. The methods of central line tracing were discussed, and the clinical application of central line extraction was divided into 1) radius extraction 2) calcification and stenosis analysis. Coronary CTA (Computed Tomography Angiography) technology can not only obtain the image of coronary artery, but also image the wall of coronary artery, assisting doctors in the analysis of vascular calcification and stenosis. Coronary CTA technology adds a diagnostic approach to cardiovascular disease and makes it more acceptable to patients because of the use of non-interventional techniques.

Nonrigid 2D/3D Registration of Coronary Artery Models With Live Fluoroscopy for Guidance of Cardiac Interventions

A 2D/3D nonrigid registration method is proposed that brings a 3D centerline model of the coronary arteries into correspondence with bi-plane fluoroscopic angiograms. The registered model is overlaid on top of interventional angiograms to provide surgical assistance during image-guided chronic total occlusion procedures, thereby reducing the uncertainty inherent in 2D interventional images. The proposed methodology is divided into two parts: global structural alignment and local nonrigid registration. In both cases, vessel centerlines are automatically extracted from the 2D fluoroscopic images, and serve as the basis for the alignment and registration algorithms. In the first part, an energy minimization method is used to estimate a global affine transformation that aligns the centerline with the angiograms. The performance of nine general purpose optimizers has been assessed for this problem, and detailed results are presented. In the second part, a fully nonrigid registration method is proposed and used to compensate for any local shape discrepancy. This method is based on a variational framework, and uses a simultaneous matching and reconstruction process to compute a nonrigid registration. With a typical run time of less than 3 s, the algorithms are fast enough for interactive applications. Experiments on five different subjects are presented and show promising results.

Real-time emergency route generating algorithm in tunnel

As part of the digital mine system, a real time emergency route generating algorithm for a large scale metal mine is studied. The tunnel is abstracted and mathematically described by the center line model. A series of definitions are made and the center lines are regularized. In order to improve the quality of the final routes, a center line dataset preprocessing is done according to the factors including the slope threshold and the tunnel closed state information, etc. While in preprocessing, the mineshaft and shaft with the steep slope are excluded implicitly. The interface is preserved for point-like objects (e.g. blowers), directions (e.g. wind direction of blowers) and so on. The final path finding algorithm is optimized by the filter operation that the calculation is only performed at the endpoints and hub points, which can further reduce computing data amount. In our experiment, 3 368 nodes out of 22 401 nodes are selected as key nodes, therefore, the data processing amount of the algorithm is reduced to 1/7 and the routes can be found in real time. The algorithm is implemented and integrated into the final digital mine system.

Field scale characterization and modeling of contaminant release from a coal tar source zone

A coal tar contaminated site was characterized using traditional and innovative investigation methods. A careful interpretation of hydrogeological and hydrogeochemical data allowed for the conceptualization of the heterogeneous coal tar distribution in the subsurface. Past and future contaminant release from the source zone was calculated using a modeling framework consisting of a three-dimensional steady-state groundwater flow model (MODFLOW) and two hydrogeochemical models (MIN3P). Computational time of long-term simulations was reduced by simplifying the coal tar composition using 3 composite and 2 individual constituents and sequential application of a 2D centerline model (for calibration and predictions) and a 3D model (only for predictions). Predictions were carried out for a period of 1000 years. The results reveal that contaminant mass flux is governed by the geometry of zones containing residual coal tar, amount of coal tar, its composition and the physicochemical properties of the constituents. The long-term predictions made using the 2D model show that even after 1000 years, source depletion will be small with respect to phenanthrene, 89% of initial mass will be still available, and for the moderately and sparingly soluble composite constituents, 60% and 98%, respectively.

Respiratory motion of the heart: Implications for magnetic resonance coronary angiography

Magnetic resonance (MR) coronary imaging is susceptible to artifacts caused by motion of the heart. The purpose of this thesis was to study the respiratory motion of the coronary arteries and to use the results to develop strategies for improved MR imaging. The first section of the thesis describes a MR motion correction technique for objects undergoing a 3D affine transformation. The remainder of the thesis focuses on measuring the respiratory motion of the heart from free breathing x‐ray angiograms. Stereo reconstruction methods are used to generate 3D models of the arteries from biplane angiograms. A method for tracking the motion of the arteries in a sequence of biplane images is presented next. The algorithm uses 3D regularizing constraints on the length changes of the arteries and on the spatial regularity of their motion. The algorithm was validated using a deforming vascular phantom. RMS 3D distance errors were measured between centerline models tracked in the x‐ray images and gold‐standard models derived from a gated 3D MR acquisition. The mean error was for four different orientations of the x‐ray system. The motion field recovered from free breathing angiograms is a combination of the cardiac contraction and respiratory motion of the heart. A cardiac respiratory parametric model is formulated to decompose the field into independent cardiac and respiratory components. Results are presented for ten patients imaged during spontaneous tidal breathing. For all patients, the heart translated caudally (mean, and rotated in a cranio‐dorsal direction (mean, during inspiration. In eight patients, the heart also translated anteriorly (mean, and rotated in a caudo‐dextral direction (mean, . Anatomic landmarks were used to compare results across patients. Three dimensional displacements and velocities were compared, and quiescent periods in the respiratory and cardiac cycles were measured. Finally, respiratory motion was analyzed using three linear motion models that correspond to available MR motion correction techniques: translation, rigid body, and affine. Calculations indicate that a two‐to‐four‐fold increase in scan efficiency is attainable, resulting in reduced scan times while maintaining image quality.

4D deformation field of coronary arteries from monoplane rotational X-ray angiography

We present a new method to automatically compute a (3D+t) 4D parametric deformation field of coronary arteries from one single rotational X-ray angiography acquisition. We first build 3D centerline models of the coronary arteries and then compute 4D deformations that make the 3D model fit the entire sequence, at all cardiac cycle phases. Taking advantage of the 4D deformation field knowledge, we propose a new clinical application in rotational X-ray angiography called “stabilized display”, presenting a focused and centered display of 3D points of interest. Results on patient data sets are presented.

Elliptic Fourier approximation with application to left ventricular contour analysis

A computer program for the quantitative analysis of left ventricular wall motion, in standard angiography or echography, was developed based on the center-line model. In order to resolve the uncertainties of the previous implementations, the elliptic Fourier approximation was tested on a large set of left ventricular contour pairs, in various pathological conditions. Fitting a function to the center-line (in the middle of end diastolic and end systolic contours) makes it possible to perform multiple tasks at the same time, in an analytical way without the need of arbitrary parameters, such as search windows. In doing so, the flexibility and accuracy of this method was demonstrated, more in general, for filtering, interpolation and differentiation of noisy 2D or 3D data. A comparison with standard B-spline was carried out, for both open and closed curves, with sparse or equispaced points. The resulting approximation errors were twice as high as those of the elliptic Fourier decomposition, still preserving smooth direction and curvature. Though already described, this methodology deserves more widespread application.

Comparison of models for quantitative left ventricular wall motion analysis from two-dimensional echocardiograms during acute myocardial infarction

To develop quantitative analysis of regional left ventricular wall motion in the absence of a gold standard, an objective statistical measure to compare models of wall motion is described. This measure can be derived from wall motion analysis of subgroups of patients with different patterns of wall motion. A priori knowledge of the exact localization of wall motion abnormalities is not needed. Two-dimensional echocardiograms were analyzed from 79 patients with myocardial infarction. The following 4 models were compared: Model I was based on the descent of the base toward the stable apex during systole. Models II and III measured area reduction with fixed- and floating-reference systems, respectively. Model IV was the centerline model. Classification by the electrocardiogram of the myocardial infarction as anterior (n = 37), posterior (n = 17) and inferior (n = 25) provided the a priori probability for classification of myocardial infarction. The a posteriori probability for classification of myocardial infarction was derived from the detection of wall motion abnormalities by echocardiographic analysis. The mean difference between a posteriori and a priori probability is a measure for the diagnostic value of the model, and was measured for 200 regions/patient. Use of the described measure revealed model I to be the most informative model and model III the least informative. Thus, the described statistical measure contributes to the development of regional wall motion analysis.

Center-line Velocity Models for Flanged Local Exhaust Openings

Abstract Local exhaust systems are important in controlling exposures. Recently, there has been a great deal of interest in predicting hood flow patterns in order to determine effectiveness. This article presents a generalized approach, based in potential flow theory, to develop the hood center-line air velocity models directly for flanged openings of practical geometries. These were the rectangle, the square, the circle, and the slot. Measurements of the center-line velocities for a flanged circular opening were conducted to determine the validity of the potential flow assumption. Agreement of the theoretical model with experimental data indicates that the potential flow approximation applies to flow into unobstructed exhaust hoods. The theoretical models for the circle, the rectangle, and the slot were also compared to the empirically based equations found in the Industrial Ventilation Manual. Good agreement between the empirical and theoretical models was noted in the case of circular openings and in t...

On the Dynamic Analysis of Curved and Twisted Cylinders Transporting Fluids

The longitudinal, torsional and 2-transverse equations of motion are formulated for the titled problem through application of Hamilton’s Principle. Curvature-torsion conditions under which linear oscillation in a plane can exist are identified. The finite element method with isoparametric elements is used for discretization prior to spectra analysis. Natural frequency calculations over a range of mass transport velocities and cylinder end conditions were carried out for comparison with constant and variable curvature analyses and experiment. These results support the application of the constant curvature, inextensible centerline model for curved cylinder vibration analysis.