Blood Flow In Left Ventricle Research Articles

Deep learning based automated left ventricle segmentation and flow quantification in 4D flow cardiac MRI

Background4D flow MRI enables assessment of cardiac function and intra-cardiac blood flow dynamics from a single acquisition. However, due to the poor contrast between the chambers and surrounding tissue, quantitative analysis relies on the segmentation derived from a registered cine MRI acquisition. This requires an additional acquisition and is prone to imperfect spatial and temporal inter-scan alignment. Therefore, in this work we developed and evaluated deep learning-based methods to segment the left ventricle (LV) from 4D flow MRI directly. MethodsWe compared five deep learning-based approaches with different network structures, data pre-processing and feature fusion methods. For the data pre-processing, the 4D flow MRI data was reformatted into a stack of short-axis view slices. Two feature fusion approaches were proposed to integrate the features from magnitude and velocity images. The networks were trained and evaluated on an in-house dataset of 101 subjects with 67,567 2D images and 3030 3D volumes. The performance was evaluated using various metrics including Dice, average surface distance (ASD), end-diastolic volume (EDV), end-systolic volume (ESV), LV ejection fraction (LVEF), LV blood flow kinetic energy (KE) and LV flow components. The Monte Carlo dropout method was used to assess the confidence and to describe the uncertainty area in the segmentation results. ResultsAmong the five models, the model combining 2D U-Net with late fusion method operating on short-axis reformatted 4D flow volumes achieved the best results with Dice of 84.52% and ASD of 3.14 mm. The best averaged absolute and relative error between manual and automated segmentation for EDV, ESV, LVEF and KE was 19.93 ml (10.39%), 17.38 ml (22.22%), 7.37% (13.93%) and 0.07 mJ (5.61%), respectively. Flow component results derived from automated segmentation showed high correlation and small average error compared to results derived from manual segmentation. ConclusionsDeep learning-based methods can achieve accurate automated LV segmentation and subsequent quantification of volumetric and hemodynamic LV parameters from 4D flow MRI without requiring an additional cine MRI acquisition.

Kinetic energy as a factor in assessing the work of the heart in patients with aortic stenosis

Goal. To analyze the evolution of the myocardial contraction force through the assessment of kinetic energy in patients with aortic stenosis based on intraventricular blood flowsMaterial and methods. According to the selection criteria, 21 healthy volunteers (age 34 ± 3) and 105 patients with aortic stenosis (age 62 ± 4) were examined before and after surgery for 7–10 days. Transthoracic echocardiography was performed on a Vivid E9 device in 2, 3 and 4 chamber positions with registration of intraventricular blood flows, calculation of the rate of change in volume and kinetic energy depending on the left ventricular EDV, pressure gradient (ΔP) on the aortic valve with an assessment of the displacement of the left ventricular endocardium contour, based on technologies for tracking speckles of ultrasonic images in the MultiVox program.Results. Our goal was to quantify kinetic energy (KE) during the entire cardiac cycle of the left ventricle (LV) using echocardiography. One of the main strengths identified in these studies is the high reproducibility of the assessment of LV blood flow and hemodynamics the average coefficient of variability 7 ± 2% for assessing LV function. Studies have shown increased diagnostic reliability without spending additional time. In systole, the KE before the LV operation was higher than normal values (0.62–0.78 J) after the operation, the KE approached the norm, averaging 0.55 J.Conclusion. Changes in intraventricular blood flow in patients with pressure overload of the heart demonstrate higher systolic energy compared to the control group. Different time values of energy in systole and diastole, observed in patients before surgery, represent an objective approach to assessing the work of the heart. The energy analysis reflects earlier signs of mechanical myocardial disorders, compared with the ejection fraction and, possibly, predict the development of cardiac remodeling. Adequate correction of the defect normalizes the work of the heart already in the early postoperative period.

Intraventricular Flow Patterns in Patients Treated with Left Ventricular Assist Devices.

The success of left ventricular assist device (LVAD) therapy is hampered by complications such as thrombosis and bleeding. Understanding blood flow interactions between the heart and the LVAD might help optimize treatment and decrease complication rates. We hypothesized that LVADs modify shear stresses and blood transit in the left ventricle (LV) by changing flow patterns and that these changes can be characterized using 2D echo color Doppler velocimetry (echo-CDV). We used echo-CDV and custom postprocessing methods to map blood flow inside the LV in patients with ongoing LVAD support (Heartmate II, N = 7). We compared it to healthy controls (N = 20) and patients with dilated cardiomyopathy (DCM, N = 20). We also analyzed intraventricular flow changes during LVAD ramp tests (baseline ± 400 rpm). LVAD support reversed the increase in blood stasis associated with DCM, but it did not reduce intraventricular shear exposure. Within the narrow range studied, the ventricular flow was mostly insensitive to changes in pump speed. Patients with significant aortic insufficiency showed abnormalities in blood stasis and shear indices. Overall, this study suggests that noninvasive flow imaging could potentially be used in combination with standard clinical methods for adjusting LVAD settings to optimize flow transport and minimize stasis on an individual basis.

Assessment of human left ventricle flow using statistical shape modelling and computational fluid dynamics

Blood flow patterns in the human left ventricle (LV) have shown relation to cardiac health. However, most studies in the literature are limited to a few patients and results are hard to generalize. This study aims to provide a new framework to generate more generalized insights into LV blood flow as a function of changes in anatomy and wall motion. In this framework, we studied the four-dimensional blood flow in LV via computational fluid dynamics (CFD) in conjunction with a statistical shape model (SSM), built from segmented LV shapes of 150 subjects. We validated results in an in-vitro dynamic phantom via time-resolved optical particle image velocimetry (PIV) measurements. This combination of CFD and the SSM may be useful for systematically assessing blood flow patterns in the LV as a function of varying anatomy and has the potential to provide valuable data for diagnosis of LV functionality.

Three-dimensional diastolic blood flow in the left ventricle

Three-dimensional blood flow in a human left ventricle is studied via a computational analysis with magnetic resonance imaging of the cardiac motion. Formation, growth and decay of vortices during the myocardial dilation are analyzed with flow patterns on various diametric planes. They are dominated by momentum transfer during flow acceleration and deceleration through the mitral orifice. The posterior and anterior vortices form an asymmetric annular vortex at the mitral orifice, providing a smooth transition for the rapid inflow to the ventricle. The development of core vortex accommodates momentum for deceleration and for acceleration at end diastolic atrial contraction. The rate of energy dissipation and that of work done by viscous stresses are small; they are approximately balanced with each other. The kinetic energy flux and the rate of work done by pressure delivered to blood from ventricular dilation is well balanced by the total energy influx at the mitral orifice and the rate change of kinetic energy in the ventricle.

ULTRAFAST IMAGING FOR INTRA-VENTRICULAR VORTEX ASSESSMENT: ADVANTAGES, FEASIBILITY AND PRELIMINARY RESULTS

Within a normal left ventricle (LV), diastolic filling is characterized by the formation of an asymmetric swirling motion adjacent to the mitral valve. This vortex optimizes LV blood flow ejection during systole. Assessment of such vortices can be performed using colour Doppler but the interrogation of the entire LV over time using conventional imaging can only be performed at a low frame rate (FR) (20 frames/s). Ultrafast imaging is an emerging ultrasound modality allowing the operator to scan the entire ventricle at a much higher FR, about 4x that obtained by conventional imaging. The goal of this pilot study was to test the feasibility of the technology and describe normal patterns of vortex within the LV.

The numerical analysis of non-Newtonian blood flow in human patient-specific left ventricle

Recently, various non-invasive tools such as the magnetic resonance image (MRI), ultrasound imaging (USI), computed tomography (CT), and the computational fluid dynamics (CFD) have been widely utilized to enhance our current understanding of the physiological parameters that affect the initiation and the progression of the cardiovascular diseases (CVDs) associated with heart failure (HF). In particular, the hemodynamics of left ventricle (LV) has attracted the attention of the researchers due to its significant role in the heart functionality. In this study, CFD owing its capability of predicting detailed flow field was adopted to model the blood flow in images-based patient-specific LV over cardiac cycle. In most published studies, the blood is modeled as Newtonian that is not entirely accurate as the blood viscosity varies with the shear rate in non-linear manner. In this paper, we studied the effect of Newtonian assumption on the degree of accuracy of intraventricular hemodynamics. In doing so, various non-Newtonian models and Newtonian model are used in the analysis of the intraventricular flow and the viscosity of the blood. Initially, we used the cardiac MRI images to reconstruct the time-resolved geometry of the patient-specific LV. After the unstructured mesh generation, the simulations were conducted in the CFD commercial solver FLUENT to analyze the intraventricular hemodynamic parameters. The findings indicate that the Newtonian assumption cannot adequately simulate the flow dynamic within the LV over the cardiac cycle, which can be attributed to the pulsatile and recirculation nature of the flow and the low blood shear rate.

Inverse Problem for Color Doppler Ultrasound-Assisted Intracardiac Blood Flow Imaging.

For the assessment of the left ventricle (LV), echocardiography has been widely used to visualize and quantify geometrical variations of LV. However, echocardiographic image itself is not sufficient to describe a swirling pattern which is a characteristic blood flow pattern inside LV without any treatment on the image. We propose a mathematical framework based on an inverse problem for three-dimensional (3D) LV blood flow reconstruction. The reconstruction model combines the incompressible Navier-Stokes equations with one-direction velocity component of the synthetic flow data (or color Doppler data) from the forward simulation (or measurement). Moreover, time-varying LV boundaries are extracted from the intensity data to determine boundary conditions of the reconstruction model. Forward simulations of intracardiac blood flow are performed using a fluid-structure interaction model in order to obtain synthetic flow data. The proposed model significantly reduces the local and global errors of the reconstructed flow fields. We demonstrate the feasibility and potential usefulness of the proposed reconstruction model in predicting dynamic swirling patterns inside the LV over a cardiac cycle.

Continuous Apex to Left Ventricle Blood Flow Pattern in Hypertrophic Cardiomyopathy with Apical Aneurysm and Midventricular Obstruction

A 42-year-old female presented with chest pain, noted to have systolic and diastolic murmurs on physical examination and left ventricular hypertrophy on the electrocardiogram. Echocardiography with contrast enhancement revealed hypertrophic cardiomyopathy (HCM) with apical aneurysm and mid left ventricular cavity obstruction. Doppler interrogation showed continuous systolic and diastolic flow from the apex to left ventricle (LV) with a transient deceleration giving rise to a notched pattern. Myocardial ischemia of the apex was demonstrated on adenosine nuclear scintigraphy without epicardial coronary obstruction on angiography. This case demonstrates a novel Doppler pattern with continuous apex to LV flow in HCM in the setting of apical ischemia that may account for the formation of the aneurysm.

Weighted Least-Squares Finite Element Method for Cardiac Blood Flow Simulation with Echocardiographic Data

As both fluid flow measurement techniques and computer simulation methods continue to improve, there is a growing need for numerical simulation approaches that can assimilate experimental data into the simulation in a flexible and mathematically consistent manner. The problem of interest here is the simulation of blood flow in the left ventricle with the assimilation of experimental data provided by ultrasound imaging of microbubbles in the blood. The weighted least-squares finite element method is used because it allows data to be assimilated in a very flexible manner so that accurate measurements are more closely matched with the numerical solution than less accurate data. This approach is applied to two different test problems: a flexible flap that is displaced by a jet of fluid and blood flow in the porcine left ventricle. By adjusting how closely the simulation matches the experimental data, one can observe potential inaccuracies in the model because the simulation without experimental data differs significantly from the simulation with the data. Additionally, the assimilation of experimental data can help the simulation capture certain small effects that are present in the experiment, but not modeled directly in the simulation.

G605 容積型ポンプの非対称性が内部流れに与える影響の数値シミュレーション(GS6-2 数値計算,一般セッション)

In this study, we aim to simulate blood flow in left ventricle. As a fundamental study, we make the simulation model of displacement pump whose capacity is changed in a cycle and simulate the internal flow using 2-dimentional Navier-Stokes equations and virtual flux method. We simulate three types of the pump, one is symmetric and the others are asymmetric. First, we validate mass conservation in terms of flow rate in all cases. Next, we discuss the influence of asymmetry of the models on internal flow. We find that velocity profile near the outlet and wall share stress on the outlet walls are strongly affected by the asymmetry.

Subject-specific computational simulation of left ventricular flow based on magnetic resonance imaging

A detailed investigation of left ventricle (LV) flow patterns could improve our understanding of the function of the heart and provide further insight into the mechanisms of heart failure. This study presents patient-specific modelling with magnetic resonance imaging (MRI) to investigate LV blood flow patterns in normal subjects. In the study, the prescribed LV wall movements based on the MRI measurements drove the blood flow in and out of the LV in computational fluid dynamics simulation. For the six subjects studied, the simulated LV flow swirls towards the aortic valve and is ejected into the ascending aorta with a vertical flow pattern that follows the left-hand rule. In diastole, the inflow adopts a reasonably straight route (with no significant secondary flow) towards the apex in the rapid filling phase with slight variations in the jet direction between different cases. When the jet reaches about two thirds of the distance from the inflow plane to the apex, the blood flow starts to change direction and swirls towards the apex. In the more slowly filling phase, a centrally located jet is evident with vortices located on both sides of the jet on an anterior-posterior plane that passes through the mitral and aortic valves. In the inferior-superior plane, a main vortex appears for most of the cases in which an anticlockwise vortex appears for three cases and a clockwise vortex occurs for one case. The simulated flow patterns agree well qualitatively with MRI-measured flow fields.

Different LV and RV response to α‐adrenergic stimulation in vivo

Objective: α‐adrenergic agonists (α‐Adr) exert positive cardiac inotropic effects. Recent data suggest that rat left ventricle (LV) and right ventricle (RV) respond differently to α‐Adr in vitro. The purpose of this study is to determine whether α‐Adr exerts different effects on the LV and RV in vivo.Methods: Pigs (n=8) were instrumented with micromanometers and sonomicrometry crystals in the LV and RV. Contractility was determined by preload‐adjusted regional external work, a loading condition‐independent index, and regional blood flow by microspheres. Measurements were obtained at baseline, after CaCl2 15 mg‐kg−1 bolus, and during phenylephrine (PHE) 3–6 μg‐kg−1‐min−1 IV for 60 min.Results: LV and RV contractility both increased similarly after CaCl2 (LV: 143±7% of baseline; RV: 145±10% of baseline); in contrast, PHE increased LV but decreased RV contractility (LV: 147±10% of baseline; RV: 90±19% of baseline; p<0.05 for paired difference) despite increased LV and RV pressure. LV and RV regional blood flow both increased during PHE (LV: 0.8±0.2 and RV 0.6±0.1 ml‐gm−1‐min−1 at baseline; LV: 1.5±0.2 and RV: 1.0±0.2 ml‐gm−1‐min−1 during PHE).Conclusions: The α‐Adr agent phenylephrine exerts positive inotropic effects on the LV but negative inotropic effects on the RV in vivo. This difference is not due to differences in loading conditions or regional myocardial blood flow. Supported by NHLBI.