Development of an in vivo method for determining material properties of passive myocardium

Abstract

Calculation of mechanical stresses and strains in the left ventricular (LV) myocardium by the finite element (FE) method relies on adequate knowledge of the material properties of myocardial tissue. In this paper we present a model-based estimation procedure to characterize the stress-strain relationship in passive LV myocardium. A 3D FE model of the LV myocardium was used, which included morphological fiber and sheet structure and a nonlinear orthotropic constitutive law with different stiffness in the fiber, sheet and sheet-normal directions. The estimation method was based on measured wall strains. We analyzed the method's ability to estimate the material parameters by generating a set of synthetic strain data by simulating the LV inflation phase with known material parameters. In this way we were able to verify the correctness of the solution and to analyze the effects of measurement and model error on the solution accuracy and stability. A sensitivity analysis was performed to investigate the observability of the material parameters and to determine which parameters to estimate. The results showed a high degree of coupling between the parameters governing the stiffness in each direction. Thus, only one parameter in each of the three directions was estimated. For the tested magnitudes of added noise and introduced model errors, the resulting estimated stress-strain characteristics in the fiber and sheet directions converged with good accuracy to the known relationship. The sheet-normal stress-strain relationship had a higher degree of uncertainty as more noise was added and model error was introduced

Fast Parameter Inference in a Biomechanical Model of the Left Ventricle by Using Statistical Emulation

“…The inverse problem itself can be solved by using a variety of methods and many studies have demonstrated that it is possible to estimate constitutive material parameters by using in vivo measurements even with very complex constitutive relations (Guccione et al, 1991;Remme et al, 2004;Sermesant et al, 2006;Sun et al, 2009). However, because of the strong correlation between the material parameters and sparse noisy data, the formulated inverse problem is highly non-linear (Xi et al, 2011;Gao et al, 2015).…”

Influence of myocardial fiber/sheet orientations on left ventricular mechanical contraction

“…The model is equipped with two sets of fiber and sheet arrangements. In the first arrangement, a generic rulebased dataset is used where fiber/sheet angles vary linearly in the transmural direction, as seen previously in, e.g., [1,[7][8][9][10][11][12][13][14][15]. Several values for the linear change of fiber/sheet angles are examined.…”

A framework for biomechanics simulations using four-chamber cardiac models

“…Identifying the myocardial material properties is still an active ongoing research topic (Remme et al, 2004;Sommer et al, 2015). Although the myocardial tissue appears to be viscoelastic (Taber, 1995), the short cardiac cycle time scale compared to the tissue relaxation time makes it less significant to be simulated as a viscoelastic material.…”