Physically-Constrained Diffeomorphic Demons for the Estimation of 3D Myocardium Strain from Cine-MRI

Analysing heart motion provides crucial insights on the condition of the cardiac function. Tagged-MRI and 2D-strain ultrasound enable quantitative assessment of the myocardium strain. But estimating 3D myocardium strain from cine-MRI remains attractive: cine-MRI is widely available and it yields detailed 3D+t anatomical images. This paper presents an image-based method to estimate myocardium strain from clinical short-axis cine-MRI. To recover non-apparent cardiac motions, we improve the diffeomorphic demons, a non-linear registration algorithm, by adding two physical constraints. First, myocardium nearincompressibility is ensured by constraining the deformations to be divergence free. Second, myocardium elasticity is modelled using smooth vector filters. The proposed physically-constrained demons are compared with the diffeomorphic demons and evaluated in a healthy subject against tagged MRI. The method is also tested on a patient with congenital pulmonary valve regurgitations and compared with 2D-strain measurements. In both cases, obtained results correlate well with ground truth. This method may become a useful tool for cardiac function evaluation.