Narrow Results

Examinations of the left ventricle (LV), which is the systemic ventricle and as such of paramount importance for the function of the heart, are commonly employed in cardiology. Numerous models have been developed that allow for LV parametric representation. Thanks to that, the left ventricle is better suited for all types of modeling endeavors and the correctness of the results may be relatively easily verified.

The authors present a new method for an automatic detection and evaluation of the left ventricle, which is seen as an echocardiographic image in the four-chamber projection. The method is based on computerized image analysis, and in particular, on mathematical morphology.^{4,6,8,9,11,12} Investigations and the preliminary verification of the method have been carried out on complete cycles registered on video in the course of examinations. It is the complete cycles only that allow us to follow the dynamics of cardiac function.

As a result of long-term collaboration with cardiologists, an algorithm has been developed that allows for an automatic LV detection. A precise delineation of its borders allows for an objective description of changes in geometric parameters in the course of the entire cycle and for a quantitative analysis of the left ventricular function.

High-level noise and low contrast characteristics in medical images continue to present major bottlenecks in their segmentation despite increased imaging modalities. This paper presents a semi-automatic algorithm that utilizes the noise for enhancing the contrast of low contrast input magnetic resonance images followed by a new graph cut method to reconstruct the surface of left ventricle. The main contribution in this work is a new formulation for preventing the conventional cellular automata method to leak into surrounding regions of similar intensity. Instead of segmenting each slice of a subject sequence individually, we empirically select a few slices, segment them, and reconstruct the left ventricular surface. During the course of surface reconstruction, we use level sets to segment the rest of the slices automatically. We have throughly evaluated the method on both York and MICCAI Grand Challenge workshop databases. The average Dice coefficient (in %) is found to be 92.4 ± 1.3 (value indicates the mean and standard deviation) whereas false positive ratio, false negative ratio, and specificity are found to be 0.019, 7.62 × 10^-3, and 0.75, respectively. Average Hausdorff distance between segmented contour and ground truth is determined to be 2.94 mm. The encouraging quantitative and qualitative results reflect the potential of the proposed method.

The geometry of canine ventricle with purkinje system provides the data basis for the simulation and analysis of the mechanisms of ventricular pathophysiology. The acquisition of the geometry of the purkinje system, however, is very challenging, and traditional construction approaches are mainly based on modeling using fractal geometry. In this paper, we propose a novel locally linear embedding (LLE)-based method to construct 3D anatomical purkinje system of the canine left ventricle (LV). First, we collect the 2D purkinje system data in a canine ventricle and extract the endocardial surface of the canine left ventricle from 3D canine ventricle. Then, LLE is used to map the 3D geometry of the endocardial surface to a 2D subspace, and the 2D purkinje system data is further embedded into this 2D subspace. Finally, LLE is adopted to map both the 3D geometry of the endocardial surface and the 2D purkinje system data back to the 3D space. An experiment is designed to verify the effectiveness of the LLE-based construction method. The proposed method approaches is promising in restoring realistic purkinje system of the left canine ventricle.

In this paper, stress and strain equations are developed for the left ventricle mainly to find the influence of the ventricle’s shape on wall stresses. Here, the ventricle is assumed to be a thick-walled truncated conical shell and large elastic deformation theory is applied. Our model is compared to corresponding results approximating the left ventricle as a spherical shell. Clinically relevant parameters such as the myocardial stiffness constant, the stretch ratios and the stresses and strains have been computed using available canine data. The conical model leads to more realistic results than the spherical model and enables one to evaluate stresses and strains from base to apex instead of only at the equatorial region as in a cylindrical model.

In this paper, we estimate the stresses and strains from the equatorial region down to the apex of the heart by modeling the passive left ventricle as a frustrum of a thick hollow cone. Large deformation theory has been employed in this analysis. Furthermore, the effects of residual stresses and the anisotropy due to muscle fiber orientation have been included. It is observed that circumferential stress, which is the most important physiologically, decreases considerably at the endocardium and is more evenly distributed through the wall when residual stresses are taken into account. The stresses also decrease as we go from the equatorial region to the apex. Because heart muscles physically have residual stresses, the consequent lower stress gradient through the wall enhances the diastolic function of the left ventricle.

A reliable and inexpensive method was developed for the realization of flexible ventricle prototypes to be used in a pulse duplicator test circuit for cardiac valve testing, with particular emphasis on the valves in the mitral position. The peculiarity of our ventricular models is their ability to preserve a physiologic-like shape during the entire cardiac cycle. Moreover, the models take into account the function of papillary muscles, thus allowing a realistic evaluation of the whole inlet valve complex (mitral valve, chordae tendineae and papillary muscles). Ventricular sacs were designed by structural analyses, driven by a set of criteria identifying the similarity to natural ventricular conformational changes. The computationally optimized ventricle shapes were used to manufacture the mould for prototypes to be subjected to experimental validation trials. The difference between simulation-predicted and experimentally measured behaviors did not exceed 6.5%, which confirmed reliability of the developed method.

This study characterizes left ventricular function in terms of passive and active elastances (E_p & E_a) and shape factor index. Both the active elastance and shape factor indices can be employed as contractility indices. The work also demonstrates how E_p and E_a can explain LV pressure dynamics in terms of LV volume dynamics.

This study extracted hemodynamic information from echocardiogram to complement the left ventricle ejection fraction and the stroke volume for cardiac evaluation and diagnosis. The dynamic characteristics of irregular wall motions can be analyzed by kinetic energy fluxes transferred from the left ventricle to the blood flow. A set of cardiac indices is developed for quantification and classification of echocardiogram for clinical application. The pumping characteristics can be further quantified through the work done by pressure and viscous stresses of the ventricle.

Left ventricular (LV) contraction is the basis of LV systolic function, impairment of which underlies heart failure pathophysiology. Its accurate quantification in the form of LV contractility indices is imperative for diagnostic and follow-up assessment of LV systolic function in heart failure.

Herein, we analyze LV contractile performance by focusing on LV contractility indices at different physiological organizational levels: from sarcomere dynamics to LV myocardial properties (such as elastic modulus and elastance), and from LV wall contractile stress development to the generation of intra-LV blood flow velocities and pressure distributions. Further, we present the development analyses of these indices and their medical applications. Using improved development of invasive and noninvasive techniques for measuring ventricular pressure, geometry, and volume, we show how these indices have become more amenable for clinical usage to obtain better patient assessment.

The purpose of this paper is to present a comprehensive coverage of LV contraction physiology, indices to qualify LV contraction, formulation, and medical applications of some major intrinsic LV contractility indices, so as to provide the basis of functional assessment of normal versus diseased hearts.

The aim of the study is to evaluate cardiac regional function of young athletes with false tendons (FT) in the left ventricle (LV). The focus was on mechanical asynchrony in LV wall. Forty-seven young athletes (mean age 20.2 ± 2.9 years) with connective tissue dysplasia syndrome underwent transthoracic echocardiography. To formalize FT topology, the 3D-model of LV geometry was reconstructed based on three short-axis sections and one long-axis section of LV. On average, 4.0 ± 1.0 FT with different localization and orientation in LV were determined. Cardiac function was estimated in 12 regions at LV long-axis section in the course of complete heart cycle. RMS variations of the regional systolic function duration (dT) and the variation coefficient of regional ejection fraction (Cv r-EF) for 12 regions served as measures of the mechanical asynchrony. Wide variety of asynchrony parameters was obtained. The value of dT varied from 24.2 to 84.1 ms (40.4 ± 27.8 ms); Cv r-EF — from 8.0% to 42.0% (20.83 ± 8.35%). Significant correlations between total number of FT per heart and dT (r = 0.396; P < 0.01) and between median transverse FT (connect interventricular septum and lateral LV wall) and Cv r-EF (r = 0.301; P < 0.05) were found. Detailed analyses of FT morphology with respect of LV regional function peculiarities showed that higher extent of asynchrony associates with the transverse and oblique FT mainly located at basal and/or medial portions of LV chamber.

Ejection of blood from the left ventricle to the aorta is studied using two-dimensional Navier–Stokes equations, the work-energy equation and the magnetic resonance imaging of a normal ventricular motion. Vortex shedding in the sinuses of Valsalva is dominated by the aortic jet, flow acceleration and valve motion. Momentums produced by ventricular contraction are in concert with vortices in the ventricle for blood ejection. Shear stresses and net pressures on the aortic valve are calculated during valve opening and closing. The rate of work done by shear and the energy dissipation in the ventricle are small. The Bernoulli energy flux delivered to blood from ventricular contraction is practically balanced by energy flux at the aortic root and the rate change of kinetic energy in the ventricle.

Numerical modeling of the left ventricle dynamics plays an important role in testing different physiological scenarios and treatment techniques before the in vitro and in vivo assessments. However, utilized left ventricle model becomes vital in the simulations because validity of the results depends on the response of the numerical model to the parameter changes and additional sub-models for the applied treatment techniques. In this study, it is aimed to evaluate different numerical left ventricle models describing healthy and failing ventricle dynamics as well as the response of these models under continuous flow left ventricular assist device support. Six different numerical left ventricle models which include time varying elastance and single fiber contraction approaches are selected and applied in combination with a closed loop electric analogue of the circulation to achieve this purpose. The time varying elastace models relate ventricular pressure and volume changes in a simplistic way while the single fiber contraction models combine different scales ranging from protein to organ level. Change of the hemodynamic signals at the organ level for healthy, failing and CF-LVAD supported left ventricle models shows functionality of these models and helps to understand usability of them for different purposes.

False tendons (FT) are additional chord-like structures in left ventricle (LV) cavity considered as a phenotypic feature of the connective tissue dysplasia (CTD) syndrome. The search for a range of heart adaptability to exercise loads of young athletes with FT in LV is the aim of the proposed study. Sixty six members of student basketball and indoor soccer teams (mean age: 19.8$\pm$3.9 years) underwent treadmill stress-test and heart ultrasound transthoracic examination. Further, image processing to perform the tendons mapping within LV 3D-reconstructed model was applied. The number of FT located in different parts of LV varied from 1 to 6 units per LV. Based on the comparative and correlation analyses of data obtained, we found that the more the number of FT per LV, the less is a range of the heart adaptation to increased exercise loads. In accordance with the results of two-way multivariate analysis of variance, we concluded that the FT, located in basal and median LV zones, connecting interventricular septum and posterior-lateral parts of LV wall mainly affect the ability of the heart to adapt to exercise loads. Therefore, athletes with certain number and types of FT in the LV critically need individual prescription for exercise loads.

Recent years have seen a renewed interest in the theories of extended continuum mechanics. These allow for a finer and relatively simple modeling of physical phenomena occurring on the microscopic level. The Eringen’s micromorphic medium belongs to this class and allows accounting for the material microstructure. A subclass of this model was applied to model the mechanical behavior of cardiac tissue. With the aid of a specifically developed numerical tool, the validity of the approach is demonstrated using different myocardial infarct scenario.

Segmentation of the left ventricle in ultrasound images for viewing through different axes is a critical aspect. This paper proposes the development of novel active contour models with shape constraint to segment the left ventricle in three different axis views of the ultrasound images. The shapes observed in all the axis views of the left ventricle were not similar. According to the cardiac cycle, the valve opening in the end-diastolic phase influenced the left ventricle segmentation; hence, a shape constraint was embedded in the active contour model to keep ventricle’s shape, especially in the Apical long-axis view and Apical four-chamber view. Furthermore, for different axes views, diverse active contour models were proposed to fit each situation. The shape constraint in each function for different views exhibited a specific shape during the function iteration. In order to speed up the algorithm evolution, previous results were used for the initialization of the present active contour. We evaluated the proposed method on 57 patients with three different views: Apical long-axis view, Apical four-chamber view and Short-axis view at the papillary muscle level and obtained the Dice similarity coefficients of $0.86\pm 0.05$, $0.90\pm 0.06$ and $0.90\pm 0.06$ and the Hausdorff distance metrics of $10.11\pm 4.66$, $7.41\pm 4.46$ and $9.98\pm 6.58$, respectively. The qualitative and quantitative evaluations showed an advantage of our method in terms of segmentation accuracy.

Investigators collect data and present them in a way that offers the best insight regarding the questions at hand. To facilitate understanding of certain aspects, it may occasionally be useful to rearrange primary data and formulate them as derived variables. For example, the travel distance divided by the invested time yields average velocity (as m/s). Problems may arise when interpreting ratios that fail to have a physical dimension. For example, current TV-sets have a fixed ratio for height and width, implying that we need an additional detail to define its size. Size then is determined by the diagonal, which can be calculated from the two sides using the Pythagorean theorem. Similarly, paired hemodynamic variables may be expressed as ratios. Again, a fixed ratio may refer to a variety of underlying primary data which require consideration if the ratio is unitless. In this survey, we evaluate several derived metrics commonly used in cardiovascular studies, and offer comprehensive analysis strategies.

Background: Patients with chronic aortic regurgitation (AR) usually have dilated left ventricle due to volume overload. Some of them will reduce in size after elimination of regurgitation, but others not. The present study evaluated the hypothesis that left ventricle end-diastolic diameter (LVEDD), left ventricle end-systolic diameter (LVESD) are related to left ventricle's peak stress (σ) both before and after operation.

Methods: Sixty-eight patients with chronic aortic regurgitation receiving valve replacement were included in the study. LVEDD, LVESD, and σ were determined by echocardiography and cuff sphygmomanometer measurement before and beyond 6 months after operation.

Results: The results showed that LVEDD, LVESD, and σ were decreased after the operation. In addition, σ and LVEDD had good linear correlation (for pre-operative data, σ = -3.02 + 0.286*LVEDD, R = 0.556, P < 0.001; for post-operative data, σ = -11.4 + 0.474*LVEDD, R = 0.736, P < 0.001).

Conclusion: LVEDD and σ had a linear relationship before and after valve replacement operation for AR patients. The higher slope in linear regression equation for post-operative σ–LVEDD relationship than that for pre-operative data may indicate improved myocardial contractile efficiency after the operation.

Blood flow in the left ventricle and aorta was analyzed numerically in an integrated manner. The simulation successfully demonstrated a series of flow events in the ventricle and aorta during a cardiac cycle in vivo. During diastole, an annular vortex was formed such that it surrounded the ventricular long axis. This vortex was asymmetrically large anteriorly, and the large vortex under the aortic valve contributed to the preferential redirection of blood to the ventricular outflow tract, thereby facilitating the ejection of ventricular blood into the aorta during systole. The flow of ejected blood through the open aortic valve had markedly skewed velocity profiles from the mid-systole, with increasing velocity on the posterior side in the mid-systole and toward the anterior side in later systole with swirling secondary flows, which led to the generation of helical flow in the aorta during later systole. These findings addressed the importance of the inclusion of intraventricular flow for the detailed analysis of the aortic flow.

This chapter will focus on the application of geometric models based on partial differential equation (PDE) for medical data processing. In particular, we present two possible approaches, the basic level set and the subjective surface models. We applied for left ventricular chamber segmentation and extraction of left ventricular volumes and derived functional parameters. The application of these shape independent models directly in the three-dimensional domain to data acquired when using a new real-time three-dimensional echocardiographic (RT3DE) system could potentially achieve the clinical need for correct and complete interpretation of LV morphology and pathology and for fast quantification of cardiac chamber volumes and ventricular function in various situations. The RT3DE system as well as the two models have been described in the chapter and the results obtained by applying the two models to RT3DE data are also presented.

It is now possible to simulate flow in various organs in detail, due to the rapid advances in computational technology. Our ultimate goal is to build a system that can assist clinicians in diagnosis, treatment planning, and as patients differ in terms of anatomical configuration and disease condition, a wide variety of patient data must be accumulated, not only for statistical analysis but also to improve the processing system. While the computer simulation of a phenomenon plays a key role in this success, it is still necessary to elucidate the mechanism that elicits a phenomenon inside the patient's body. This paper gives brief descriptions of heart anatomy and physiology, reviews the past in vivo, in vitro and numerical studies on the left ventricular flow and introduces the recent attempts on computational fluid modeling of the left ventricular flow and its clinical applications. The studies demonstrate that computational modeling of intraventricular flow has great potential to advance clinical diagnosis of the left ventricular function.