Quantification of cardiomyocyte contraction based on image correlation analysis

Quantification of cardiomyocyte contraction is usually obtained by measuring globally cell shortening from the displacement of cell extremities. We developed a correlation-based optical flow method, which correlates the whole-cell temporal pattern with a precise quantification of the intracellular strain wave at the sarcomeres level. A two-dimensional image correlation analysis of cardiomyocytes phase-contrast images was developed to extract local cell deformations from videomicroscopy time-lapse sequences. Test images, synthesized from known intensity displacement fields, were first used to validate the method. Intracellular strain fields were then computed from videomicroscopy time-lapse sequences of single adult and neonatal cardiomyocytes. The propagation of the sarcomeres contraction-relaxation wave during cell contraction has been successfully quantified. The time-varying patterns of intracellular displacement were obtained accurately, even when cardiomyocyte bending occurred in pace with contraction. Interestingly, the characterization of the successive 2D displacement fields show a direct quantification of the variation with time of intracellular strains anywhere in the cell. The proposed method enables a quantitative analysis of cardiomyocyte contraction without requiring wave tracking with the use of fluorescent calcium probes. Thus, our algorithmic approach provides a fast and efficient tool for analyzing the correlation between global cell dynamical behavior and mechanosensitive intracellular processes.