Validation of Image-Based Method for Extraction of Coronary Morphometry

An accurate analysis of the spatial distribution of blood flow in any organ must be based on detailed morphometry (diameters, lengths, vessel numbers, and branching pattern) of the organ vasculature. Despite the significance of detailed morphometric data, there is relative scarcity of data on 3D vascular anatomy. One of the major reasons is that the process of morphometric data collection is labor intensive. The objective of this study is to validate a novel segmentation algorithm for semi-automation of morphometric data extraction. The utility of the method is demonstrated in porcine coronary arteries imaged by computerized tomography (CT). The coronary arteries of five porcine hearts were injected with a contrast-enhancing polymer. The coronary arterial tree proximal to 1 mm was extracted from the 3D CT images. By determining the centerlines of the extracted vessels, the vessel radii and lengths were identified for various vessel segments. The extraction algorithm described in this paper is based on a topological analysis of a vector field generated by normal vectors of the extracted vessel wall. With this approach, special focus is placed on achieving the highest accuracy of the measured values. To validate the algorithm, the results were compared to optical measurements of the main trunk of the coronary arteries with microscopy. The agreement was found to be excellent with a root mean square deviation between computed vessel diameters and optical measurements of 0.16 mm (<10% of the mean value) and an average deviation of 0.08 mm. The utility and future applications of the proposed method to speed up morphometric measurements of vascular trees are discussed.     

Large-Scale 3-D Geometric Reconstruction of the Porcine Coronary Arterial Vasculature Based on Detailed Anatomical Data

The temporal and spatial distribution of coronary blood flow, pressure, and volume are determined by the branching pattern and three-dimensional (3-D) geometry of the coronary vasculature, and by the mechanics of heart wall and vascular tone. Consequently, a realistic simulation of coronary blood flow requires, as a first step, an accurate representation of the coronary vasculature in a 3-D model of the beating heart. In the present study, a large-scale stochastic reconstruction of the asymmetric coronary arterial trees (right coronary artery, RCA; left anterior descending, LAD; and left circumflex, LCx) of the porcine heart has been carried out to set the stage for future hemodynamic analysis. The model spans the entire coronary arterial tree down to the capillary vessels. The 3-D tree structure was reconstructed initially in rectangular slab geometry by means of global geometrical optimization using parallel simulated annealing (SA) algorithm. The SA optimization was subject to constraints prescribed by previously measured morphometric features of the coronary arterial trees. Subsequently, the reconstructed trees were mapped onto a prolate spheroid geometry of the heart. The transformed geometry was determined through least squares minimization of the related changes in both segments lengths and their angular characteristics. Vessel diameters were assigned based on a novel representation of diameter asymmetry along bifurcations. The reconstructed RCA, LAD and LCx arterial trees show qualitative resemblance to native coronary networks, and their morphological statistics are consistent with the measured data. The present model constitutes the first most extensive reconstruction of the entire coronary arterial system which will serve as a geometric foundation for future studies of flow in an anatomically accurate 3-D coronary vascular model.     

Intramyocardial Influences on Blood Flow Distributions in the Myocardial Wall

Flow velocity wave forms of coronary arterial inflow and venous outflow of myocardium are influenced by cardiac contraction and relaxation: arterial flow is exclusively diastolic; venous outflow is systolic. We first discuss the intramyocardial microvascular flow dynamics, then present some results of visualization of transmural microvessels by our needle-probe charge coupled device (CCD) microscope, along with an interpretation of the arteriolar and venular hemodynamics through a cardiac cycle. After describing a hierarchical system of coronary microvessels (small artery, arteriole, and capillary), we emphasize the importance of spatial heterogeneity of blood supply to myocardium with reference to a minimal vascular control unit (400 m). An understanding of mechanoenergetic interaction is fundamentally important to an understanding of intramyocardial coronary circulation, and the Physiome Project will provide powerful tools for understanding the integrated role of the intramyocardial microcirculation system. © 2000 Biomedical Engineering Society. PAC00: 8719Hh, 8719Ff, 8719Tt     

Microsurgical anatomy as the anatomical basis for microsurgery

The article presents the notions, contents and methods of studying microsurgical anatomy, which comprises macromicroscopic construction of an organ, biomechanic and morphometric characteristics of its structures, extraorgan macromicroscopic topography, intraorgan histotopography, macromicroscopic angio- and neuroarchitecture. The peculiarities of microsurgical anatomy of different organs and its clinical applications have been described.     

Remodeling of the Bifurcation Asymmetry of Right Coronary Ventricular Branches in Hypertrophy

To document the remodeling of the asymmetric branching pattern of the coronary right ventricular branches (RVBs) in right ventricular hypertrophy (RVH), we computed an asymmetry ratio, S, for the diameters and lengths of all vessels, defined as the ratio of the daughter diameters and lengths, respectively. We have previously induced RVH in pigs by pulmonary stenosis for five weeks. At autopsy, silicone elastomer casts of the right coronary arteries were made and the morphometric data on the branching pattern and vascular geometry of the RVB were collected. Data on smaller vessels were obtained from histological specimens while data on larger vessels were obtained from vascular casts. The results show that the diameter asymmetry ratio was significantly decreased in RVH hearts. The asymmetry ratios of diameters and lengths were used to compute the asymmetry ratios for vascular resistance and flow of the various daughter vessels. It was found that the degree of asymmetry of the resistance and flow were decreased, which implies that the flow heterogeneity at a bifurcation is decreased in the RVH hearts. © 2000 Biomedical Engineering Society. PAC00: 8719Uv, 8719Hh     

A Model for Transport and Dispersion in the Circulatory System Based on the Vascular Fractal Tree

Materials are distributed throughout the body of mammals by fractal networks of branching tubes. Based on the scaling laws of the fractal structure, the vascular tree is reduced to an equivalent one-dimensional, tube model. A dispersion–convection partial differential equation with constant coefficients describes the heterogeneous concentration profile of an intravascular tracer in the vascular tree. A simple model for the mammalian circulatory system is built in entirely physiological terms consisting of a ring shaped, one-dimensional tube which corresponds to the arterial, venular, and pulmonary trees, successively. The model incorporates the blood flow heterogeneity of the mammalian circulatory system. Model predictions are fitted to published concentration-time data of indocyanine green injected in humans and dogs. Close agreement was found with parameter values within the expected physiological range. © 2003 Biomedical Engineering Society. PAC2003: 8710+e, 8719Hh, 8719Uv     

Development of an Image-Based Network Model of Retinal Vasculature

The paper presents an image-based network model of retinal vasculature taking account of the 3D vascular distribution of the retina. Mouse retinas were prepared using flat-mount technique and vascular images were obtained using confocal microscopy. The vascular morphometric information obtained from confocal images was used for the model development. The network model developed directly represents the vascular geometry of all the large vessels of the arteriolar and venular trees and models the capillaries using uniformly distributed meshes. The vasculatures in different layers of the retina, namely the superficial, intermediate, and deep layer, were modeled separately in the network and were linked through connecting vessels. The branching data of the vasculatures was recorded using the method of connectivity matrix of network (the graph theory). Such an approach is able to take into account the detailed vasculature of individual retinas concerned. Using the network model developed, a circulation analysis based on Poiseuille’s equation was carried out. The investigations produced predictions of spatial distribution of the pressure, flow, and wall shear stress in the entire retinal vasculature. The method developed can be used as a tool for continuous monitoring of the retinal circulation for clinical assessments as well as experimental studies.     

Morphometric Studies of Human Coronary Artery Trees in Healthy and Disease

Objective According to the report from American Heart Association(AHA),cardiovascular diseases(CVDs)are the leading causes of death globally,and coronary artery disease(CAD),known as coronary atherosclerotic plaques,accounts for over 30%of cardiovascular diseases.Therefore,it is of great clinical significance to study the relationship between coronary bifurcations morphometrical feature change and coronary artery disease.Although coronary atherosclerosis has been extensively investigated,there is a lack of in-deep study on the differences in morphometric features between optimal and realistic geometry of coronary arterial trees.The purpose of the present paper is to determine the morphological changes in patients with CAD lesion compared with non-coronary artery disease(non-CAD)subjects.Methods Due to the difficulty of studying the coronary bifurcations in vivo,image-based in vitro anatomical 3D models have been widely used as a noninvasive method for morphometric measurement and clinical diagnosis of the coronary bifurcations.With the development of coronary computed tomography angiography(CTA)hardware and software technologies,the CTA imaging technique has been shown a promising application in the characterization,visualization,and identification of coronary artery disease in recent decades.The CTA images used to reconstruct three-dimensional(3D)coronary arterial trees are from Asia populations(Southern Chinese populations),including five cadavers without CAD lesion and 102 patients with CAD lesion.The best fit artery diameter was calculated as twice the average radius between the points in the centerlines and the points on the coronary arterial inner wall.The bifurcation angles between larger daughter artery and smaller daughter artery were determined by the intersection angle of their centerlines.Murray's law was introduced to assess the deviation of the realistic vascular networks from its optimal state.Results Based on the morphometric analysis of coronary artery bifurcations in non-CAD subjects and patients with CAD lesion subjects,the most important finding is that morphological feature parameters of non-CAD subjects are closer to the optimal values than those of patients with CAD lesion.Moreover,by comparing the morphometric data between the left and right coronary arteries,the right coronary artery exhibits a structure closer to the optimal one in morphological feature than the left coronary artery.In addition,coronary arterial trees with CAD lesion have higher asymmetry and larger area expansion ratio(AER)than those of the coronary arterial trees without CAD lesion.Conclusions We morphologically found that the coronary arterial trees with CAD lesion and left are more likely to deviate from the optimal structure predicted by Murray's law than those without CAD lesion and right.The degree to which coronary arterial system deviating from their optimal state may directly affect the incidence of coronary artery disease.This computer morpho-logical analysis strategy is illustrated to be effective in the distinguishing of the geometric differences between the healthy and diseased coronary arteries,and the analysis method may have a large potential in cardiovascular disease earlier diagnosis.     

Development of a model of the coronary arterial tree for the 4D XCAT phantom

A detailed three-dimensional (3D) model of the coronary artery tree with cardiac motion has great potential for applications in a wide variety of medical imaging research areas. In this work, we first developed a computer-generated 3D model of the coronary arterial tree for the heart in the extended cardiac-torso (XCAT) phantom, thereby creating a realistic computer model of the human anatomy. The coronary arterial tree model was based on two datasets: (1) a gated cardiac dual-source computed tomography (CT) angiographic dataset obtained from a normal human subject and (2) statistical morphometric data of porcine hearts. The initial proximal segments of the vasculature and the anatomical details of the boundaries of the ventricles were defined by segmenting the CT data. An iterative rule-based generation method was developed and applied to extend the coronary arterial tree beyond the initial proximal segments. The algorithm was governed by three factors: (1) statistical morphometric measurements of the connectivity, lengths and diameters of the arterial segments; (2) avoidance forces from other vessel segments and the boundaries of the myocardium, and (3) optimality principles which minimize the drag force at the bifurcations of the generated tree. Using this algorithm, the 3D computational model of the largest six orders of the coronary arterial tree was generated, which spread across the myocardium of the left and right ventricles. The 3D coronary arterial tree model was then extended to 4D to simulate different cardiac phases by deforming the original 3D model according to the motion vector map of the 4D cardiac model of the XCAT phantom at the corresponding phases. As a result, a detailed and realistic 4D model of the coronary arterial tree was developed for the XCAT phantom by imposing constraints of anatomical and physiological characteristics of the coronary vasculature. This new 4D coronary artery tree model provides a unique simulation tool that can be used in the development and evaluation of instrumentation and methods for imaging normal and pathological hearts with myocardial perfusion defects.     

A numerical identification syterm for airways in the lung

A numerical sytem for identifying airways at any level in the tracheobronchial tree has been develop which appears to be simple, logical, and accurate. The system has successfully used in the author' laboratory to expedite morphometric studyes of the conduciting airways in the tracheobronchial tree. Three simpe and direct criteria or rules have been fomulated for assignment of an airway identification number (AIN) to any specific pulmonary airway, according to this identification system. Some specific applications of this AIN system have been enumerated and several limitations that the authors have recoginzed have been described. Workers in the fields of bronchial morphometry and anatomy are invited to consider the possible theoretic and practical utility of this airway identification system.