Abstract
Myocardial stiffness is a valuable clinical biomarker for the monitoring and stratification of heart failure (HF). Cardiac finite element models provide a biomechanical framework for the assessment of stiffness through the determination of the myocardial constitutive model parameters. The reported parameter intercorrelations in popular constitutive relations, however, obstruct the unique estimation of material parameters and limit the reliable translation of this stiffness metric to clinical practice. Focusing on the role of the cost function (CF) in parameter identifiability, we investigate the performance of a set of geometric indices (based on displacements, strains, cavity volume, wall thickness and apicobasal dimension of the ventricle) and a novel CF derived from energy conservation. Our results, with a commonly used transversely isotropic material model (proposed by Guccione et al.), demonstrate that a single geometry-based CF is unable to uniquely constrain the parameter space. The energy-based CF, conversely, isolates one of the parameters and in conjunction with one of the geometric metrics provides a unique estimation of the parameter set. This gives rise to a new methodology for estimating myocardial material parameters based on the combination of deformation and energetics analysis. The accuracy of the pipeline is demonstrated in silico, and its robustness in vivo, in a total of 8 clinical data sets (7 HF and one control). The mean identified parameters of the Guccione material law were C_1=3000pm 1700,hbox {Pa} and alpha =45pm 25 (b_f=25pm 14, b_{ft}=11pm 6, b_{t}=9pm 5) for the HF cases and C_1=1700,hbox {Pa} and alpha =15 (b_f=8, b_{ft}=4, b_{t}=3) for the healthy case.
Highlights
Left ventricular (LV) stiffness is proposed as a diagnostic indicator of cardiac function in heart failure (HF) patients (Westermann et al 2008)
Due to its formulation the energy-based cost function (CF) is independent of the C1 parameter, as is evident by the fact that its minimization contour is parallel to the C1 axis and the minimum occurs for a unique value of α
To determine the geometric CF to pair with the energy-based CF we evaluated the six proposed geometric CFs on the 8 clinical data sets
Summary
Left ventricular (LV) stiffness is proposed as a diagnostic indicator of cardiac function in heart failure (HF) patients (Westermann et al 2008). An increment in ventricular size due to myocardial hypertrophy or an increase in collagen content with fibrosis may both lead to an equivalently stiffer LV behaviour using this methodology Differentiating between these two components, anatomical and material, may improve the identification of HF aetiology in patients. The development of biophysical models (Chen et al 2016; Crozier et al 2016; Krishnamurthy et al 2013; Lee et al 2015; Nordsletten et al 2011; Plank et al 2009) for the simulation of cardiac mechanics allows the distinct representation of the geometric and material components of stiffness Using these models, the assessment of myocardial stiffness is posed as an inverse problem, where the material parameters are determined from known mechanical loads and deformations.
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