Validation of Finite Element Image Registration-based Cardiac Strain Estimation from Magnetic Resonance Images

International audienceAccurate assessment of regional and global function of the heart is an important readout for the diagnosis and routine evaluation of cardiac patients. Indeed, recent clinical and experimental studies suggest that compared to global metrics, regional measures of function could allow for more accurate diagnosis and early intervention for many cardiac diseases. Although global strain measures derived from tagged magnetic resonance (MR) imaging have been shown to be reproducible for the majority of image registration techniques, the measurement of regional heterogeneity of strain is less robust. Moreover, radial strain is underestimated with the current techniques even globally. Finite element (FE)-based techniques offer a mechanistic approach for the regularization of the ill-posed registration problem. This paper presents the validation of a recently proposed FE-based image registration method with mechanical regularization named equilibrated warping. For this purpose, synthetic 3D-tagged MR images are generated from a reference biomechanical model of the left ventricle (LV). The performance of the registration algorithm is consequently tested on the images with different signal-to-noise ratios (SNRs), revealing the robustness of the method

Computational Modeling of Myocardial Infarction

Recent developments in computer technology and mathematical modeling have lead to a remarkable improvement in the computational modeling of the cardiovascular system. The virtual heart models have huge potential to understand the electrophysiological and mechanical response of the heart in the healthy and pathological cases. The simulation of physidogical behavior of the heart depends on the usage of physiologically sound constitutive models besides the incorporation of the efficient, robust, and stable numerical algorithms. In this contribution, the conservation of linear momentum and excitation equation in the Eulerian setting arc solved monolithically through an entirely finite-element based implicit algorithm. The incorporation of the novel generalized Hill model enables us to combine the advantageous features of the active stress and active-strain models. The evolution of the left ventricular pressure is incorporated by a Windkessel-like model. The proposed model is then used to investigate the effect of the myocardial infarction on the pressure-volume curves. (C) 2014 The Authors. Published by Elsevier B.V

Computational modeling of coupled cardiac electromechanics incorporating cardiac dysfunctions

Computational models have huge potential to improve our understanding of the coupled biological, electrical, and mechanical underpinning mechanisms of cardiac function and diseases. This contribution is concerned with the computational modeling of different cardiac dysfunctions related to the excitation-contraction coupling in the heart. To this end, the coupled problem of cardiac electromechanics is formulated through the conservation of linear momentum equation and the excitation equation formulated in the Eulerian setting and solved monolithically through an entirely finite element-based implicit algorithm. To model the electromechanical coupling, we use the recently proposed, novel generalized Hill model that is based on the multiplicative decomposition of the deformation gradient into the active and passive parts and on the additive split of the free energy function. This framework enables us to combine the advantageous features of the active-stress and the active-strain models suggested in literature. The proposed coupled approach is further supplemented by the Windkesel-based model to account for the pressure evolution within the ventricular chambers during the cardiac cycle. This allows us to generate the pressure-volume curves as a diagnostic tool to detect possible cardiac dysfunctions and to assess the efficiency of the heart function. The proposed model is employed to investigate different pathological cases that include infarction, eccentric hypertrophy, and concentric hypertrophy. The effects of these distinct cardiac dysfunctions on the pressure-volume curves and on the overall excitation-contraction of the heart are computationally examined and compared to the clinical observations reported in literature. (C) 2014 Elsevier Masson SAS. All rights reserved

Equilibrated Warping: Finite Element Image Registration with Equilibrium Gap Regularization

International audienceImage processing, in particular motion tracking, is playing an important role in biomedical engineering and in other domains such as materials and mechanical engineering. However, despite important progress made in the past decades, robustness, efficiency and precision of the existing methods must still be improved to translate them into medical and engineering applications [1]. Equilibrated Warping is a novel image registration approach, based on the finite element method and the equilibrium gap regularization [2]. The finite element method is used to formulate the image registration problem, i.e., to find the displacement field that best match the source and target images, allowing to ensure some regularity to the solution. However, because of image limited resolution and noise, this problem is ill-posed, and require regularization. The equilibrium gap regularization essentially penalizes any deviation from the solution of a hyperelastic body in equilibrium with arbitrary loads prescribed at the boundary [3]. It thus represents a regularization with strong mechanical basis. In the presentation, we will first describe the consistent linearization and discretization of the regularized image correlation problem. On simple synthetic images examples, we will show that the equilibrated warping method is effective and robust: regularization strength and image noise have minimal impact on motion tracking, especially when compared to strain-based regularization methods such as hyperelastic warping, or methods based on incompressibility constraint. We will also show results of the equilibrated warping method applied to in vivo tagged (3D CSPAMM, see Figure) and untagged (CINE) cardiac magnetic resonance images of a healthy volunteer: the method allows to extract main deformation features of the left ventricle, including radial thickening, circumferential and longitudinal shortening, as well as ventricular twist. It is also able to extract finer features of deformation, such as (i) larger radial strains in the free wall compared to the septum (because of the right ventricular pressure, this is only seen in untagged images); (ii) longitudinal variations of the radial-circumferential shear strain from apex to base. Finally, we will show that equilibrated warping compares very well with other image registration methods on a public cardiac motion tracking challenge data [1]

Quantification of Left Ventricular Strain by Joint Analysis of 3D Tagging and Cine MR Images

International audienc

Validation of cardiac strain estimation from 3D-tagged magnetic resonance images using finite element image correlation

International audienc

Quantification of Left Ventricular Strain by Joint Analysis of 3D Tagging and Cine MR Images

International audienc

Left Ventricular Torsion Obtained Using Equilibrated Warping in Patients with Repaired Tetralogy of Fallot

International audiencePurpose:Patients after surgical repair of Tetralogy of Fallot (rTOF) may suffer a decrease in left ventricular (LV) function. The aim of our study is to evaluate a novel method of assessing LV torsion in patients with rTOF, as an early indicator of systolic LV dysfunction. Methods:Motion tracking based on image registration regularized by the equilibrium gap principle, known as equilibrated warping, was employed to assess LV torsion. Seventy-six cases of rTOF and ten normal controls were included. The group of controls was assessed for reproducibility using both equilibrated warping and standard clinical tissue tracking software (CVI42, version 5.10.1, Calgary, Canada). Patients were dichotomized into two groups: normal vs. loss of torsion.Results:Torsion by equilibrated warping was successfully obtained in 68 of 76 (89%) patients and 9 of 10 (90%) controls. For equilibrated warping, the intra- and inter-observer coefficients of variation were 0.095 and 0.117, respectively; compared to 0.260 and 0.831 for tissue tracking by standard clinical software. The intra- and inter-observer intraclass correlation coefficients for equilibrated warping were 0.862 and 0.831, respectively; compared to 0.992 and 0.648 for tissue tracking. Loss of torsion was noted in 32 of the 68 (47%) patients with rTOF. There was no difference in LV or RV volumes or ejection fraction between these groups.Conclusion:The assessment of LV torsion by equilibrated warping is feasible and shows good reliability. Loss of torsion is common in patients with rTOF and its robust assessment might contribute into uncovering heart failure in an earlier stage