Assessing the performance of ultrafast vector flow imaging in the neonatal heart via multiphysics modeling and In vitro experiments

Ultrafast vector flow imaging would benefit newborn patients with congenital heart disorders, but still requires thorough validation before translation to clinical practice. This paper investigates 2-D speckle tracking (ST) of intraventricular blood flow in neonates when transmitting diverging waves at ultrafast frame rate. Computational and in vitro studies enabled us to quantify the performance and identify artifacts related to the flow and the imaging sequence. First, synthetic ultrasound images of a neonate's left ventricular flow pattern were obtained with the ultrasound simulator Field II by propagating point scatterers according to 3-D intraventricular flow fields obtained with computational fluid dynamics (CFD). Noncompounded diverging waves (opening angle of 60 degrees) were transmitted at a pulse repetition frequency of 9 kHz. ST of the B-mode data provided 2-D flow estimates at 180 Hz, which were compared with the CFD flow field. We demonstrated that the diastolic inflow jet showed a strong bias in the lateral velocity estimates at the edges of the jet, as confirmed by additional in vitro tests on a jet flow phantom. Furthermore, ST performance was highly dependent on the cardiac phase with low flows (< 5 cm/s), high spatial flow gradients, and out-of-plane flow as deteriorating factors. Despite the observed artifacts, a good overall performance of 2-D ST was obtained with a median magnitude underestimation and angular deviation of, respectively, 28% and 13.5 degrees during systole and 16% and 10.5 degrees during diastole

Patient-specific CFD simulation of intraventricular haemodynamics based on 3D ultrasound imaging

Background: The goal of this paper is to present a computational fluid dynamic (CFD) model with moving boundaries to study the intraventricular flows in a patient-specific framework. Starting from the segmentation of real-time transesophageal echocardiographic images, a CFD model including the complete left ventricle and the moving 3D mitral valve was realized. Their motion, known as a function of time from the segmented ultrasound images, was imposed as a boundary condition in an Arbitrary Lagrangian-Eulerian framework. Results: The model allowed for a realistic description of the displacement of the structures of interest and for an effective analysis of the intraventricular flows throughout the cardiac cycle. The model provides detailed intraventricular flow features, and highlights the importance of the 3D valve apparatus for the vortex dynamics and apical flow. Conclusions: The proposed method could describe the haemodynamics of the left ventricle during the cardiac cycle. The methodology might therefore be of particular importance in patient treatment planning to assess the impact of mitral valve treatment on intraventricular flow dynamics

Three-dimensional structure of the flow inside the left ventricle of the human heart

The laboratory models of the human heart left ventricle developed in the last decades gave a valuable contribution to the comprehension of the role of the fluid dynamics in the cardiac function and to support the interpretation of the data obtained in vivo. Nevertheless, some questions are still open and new ones stem from the continuous improvements in the diagnostic imaging techniques. Many of these unresolved issues are related to the three-dimensional structure of the left-ventricular flow during the cardiac cycle. In this paper we investigated in detail this aspect using a laboratory model. The ventricle was simulated by a flexible sack varying its volume in time according to a physiologically shaped law. Velocities measured during several cycles on series of parallel planes, taken from two orthogonal points of view, were combined together in order to reconstruct the phase averaged, three-dimensional velocity field. During the diastole, three main steps are recognized in the evolution of the vortical structures: i) straight propagation in the direction of the long axis of a vortex-ring originated from the mitral orifice; ii) asymmetric development of the vortex-ring on an inclined plane; iii) single vortex formation. The analysis of three-dimensional data gives the experimental evidence of the reorganization of the flow in a single vortex persisting until the end of the diastole. This flow pattern seems to optimize the cardiac function since it directs velocity towards the aortic valve just before the systole and minimizes the fraction of blood residing within the ventricle for more cycles

Left Ventricular Fluid Mechanics: the long way from theoretical models to clinical applications

\u2014The flow inside the left ventricle is characterized by the formation of vortices that smoothly accompany blood from the mitral inlet to the aortic outlet. Computational fluid dynamics permitted to shed some light on the fundamental processes involved with vortex motion. More recently, patient-specific numerical simulations are becoming an increasingly feasible tool that can be integrated with the developing imaging technologies. The existing computational methods are reviewed in the perspective of their potential role as a novel aid for advanced clinical analysis. The current results obtained by simulation methods either alone or in combination with medical imaging are summarized. Open problems are highlighted and perspective clinical applications are discussed

Three-dimensional echocardiography for the assessment of congenital and acquired heart disease

Although conventional two-dimensional and Doppler blood-flow echocardiography are the standard imaging approaches in the assessment of heart disease they do not provide anatomic reconstructions in a form that resembles the cardiac morphology as visualized by the surgeon.The work presented in this thesis has explored the hypotheses that threedimensional echocardiography facilitates spatial recognition of intracardiac structures and therefore enhances the diagnostic confidence of echocardiography in congenital and acquired heart disease. The accuracy of three-dimensional reconstructions has been validated in vitro using two different phantoms and in vivo comparing the results with other established diagnostic techniques or surgical findings. Additionally, as the main limitation of transthoracic three-dimensional echocardiography is poor image quality in a substantial proportion of adult patients, Doppler myocardial imaging has been tested as a potentially superior method to conventional grey-scale imaging for transthoracic three-dimensional image acquisition.In vitro, using a virtual computer-generated phantom and a dynamic tissuemimicking phantom, the accuracy of both linear measurements and volume computation obtained from three-dimensional images was established. For both grey-scale and Doppler myocardial imaging, a detail of 1.0 mm dimension and two details separated from each other by a distance of 1.0 mm were the smallest structures and distances identified from a three-dimensional image. When testing the accuracy of volume measurements it appeared that both techniques marginally underestimated the true phantom volume (by approximately 1.0 ml for Doppler myocardial imaging and 4.0 ml for grey-scale imaging), but the systematic error was smaller and more constant in the case of Doppler myocardial imaging over the range of different true volumes.In vivo, the study was designed to compare the accuracy of grey-scale and Doppler myocardial imaging three-dimensional left ventricular volume measurements and cineventriculography. The differences were significantly smaller for the Doppler technique during both end-diastole and end-systole. A series of congenital heart lesions has also been studied. It has been shown that dynamic surgical reconstruction of the secundum atrial septal defect is feasible from the transthoracic approach in all patients. However, in adults, Doppler myocardial imaging proved more effective than grey-scale imaging in the accuracy of threedimensional defect reconstruction. In patients with sinus venosus atrial septal defect, transthoracic three-dimensional echocardiography was more accurate than standard echocardiography in diagnosing the defect including a detailed description of the abnormal pulmonary venous drainage. Finally, in children with atrio-ventricular septal defects, the 'unroofed' atrial reconstruction of the common valve accurately displayed dynamic valve morphology en face and the mechanism of valve reflux

Echocardiography

The book "Echocardiography - New Techniques" brings worldwide contributions from highly acclaimed clinical and imaging science investigators, and representatives from academic medical centers. Each chapter is designed and written to be accessible to those with a basic knowledge of echocardiography. Additionally, the chapters are meant to be stimulating and educational to the experts and investigators in the field of echocardiography. This book is aimed primarily at cardiology fellows on their basic echocardiography rotation, fellows in general internal medicine, radiology and emergency medicine, and experts in the arena of echocardiography. Over the last few decades, the rate of technological advancements has developed dramatically, resulting in new techniques and improved echocardiographic imaging. The authors of this book focused on presenting the most advanced techniques useful in today's research and in daily clinical practice. These advanced techniques are utilized in the detection of different cardiac pathologies in patients, in contributing to their clinical decision, as well as follow-up and outcome predictions. In addition to the advanced techniques covered, this book expounds upon several special pathologies with respect to the functions of echocardiography

An Image Based Computational Fluid Dynamics Study of Mitral Valve. A novel Approach to Assess the Mitral Valve, from Physiology to Surgical Practice

Mitral valve disease is the second most frequent valve disease requiring surgery. The aim of our study was to develop through a computational fluid dynamics a method to study the mitral valve from Pathophysiology to mitral valve regurgitation undergone surgical repair. As a first stage, we performed computational fluid dynamic (CFD) simulations in the left ventricle, left atrium and aortic root, with a resistive immersed method, a turbulence model, and with imposed systolic wall motion reconstructed from Cine-Magnetic Resonance Imaging (MRI) images, which allowed us to segment also the mitral valve. For the regurgitant scenarios we considered an increase of the heart rate and a dilation of the left ventricle. Our results highlighted that mitral varve regurgitation (MVR) gave rise to regurgitant jets through the mitral orifice impinging against the atrial walls and scratching against the mitral valve leading to high values of wall shear stresses (WSSs) with respect to the healthy case. CFD with prescribed wall motion and immersed mitral valve revealed to be an effective tool to quantitatively describe hemodynamics in case of MVR and to compare different regurgitant scenarios. Our findings highlighted in particular the presence of transition to turbulence in the atrium and allowed us to quantify some important cardiac indices such as cardiac output and WSS. After validation of the model, we performed a computational image-based study of blood dynamics in the whole left heart, both in a healthy subject and in a patient with MVR. We elaborated dynamic cine-MRI images with the aim of reconstructing the geometry and the corresponding motion of left ventricle, left atrium, mitral and aortic valves, and aortic root of the subjects. This allowed us to prescribe such motion to computational blood dynamics simulations where, for the first time, the whole left heart motion of the subject is considered, allowing us to obtain reliable subject-specific information. The final aim was to investigate and compare between the subjects the occurrence of turbulence and the risk of hemolysis and of thrombi formation. In particular, we modeled blood with the Navier-Stokes equations in the Arbitrary Lagrangian-Eulerian framework, with a Large Eddy Simulation model to describe the transition to turbulence and a resistive method to manage the valve dynamics, and we used a Finite Elements discretization implemented in an in-house code for the numerical solution. Our results highlighted that the regurgitant jet in the MVR case gave rise to a large amount of transition to turbulence in the left atrium resulting in a higher risk of formation of hemolysis. Moreover, MVR promoted a more complete washout of stagnant flows in the left atrium during the systolic phase and in the left ventricle apex during diastole. This work put the base for a new clinical approach to the mitral valve such as the analysis and the comparison of different surgical techniques of the diseased mitral valve undergone a surgical repair