Image processing techniques for assessing contractility in isolated adult cardiac myocytes

Abstract

We describe a computational framework for the comprehensive assessment of contractile responses of enzymatically dissociated adult cardiac myocytes. The proposed methodology comprises the following stages: digital video recording of the contracting cell, edge preserving total variation-based image smoothing, segmentation of the smoothed images, contour extraction from the segmented images, shape representation by Fourier descriptors, and contractility assessment. The different stages are variants of mathematically sound and computationally robust algorithms very well established in the image processing community. The physiologic application of the methodology is evaluated by assessing overall contraction in enzymatically dissociated adult rat cardiocytes. Our results demonstrate the effectiveness of the proposed approach in characterizing the true, two-dimensional, "shortening" in the contraction process of adult cardiocytes. We compare the performance of the proposed method to that of a popular edge detection system in the literature. The proposed method not only provides a more comprehensive assessment of the myocyte contraction process but also can potentially eliminate historical concerns and sources of errors caused by myocyte rotation or translation during contraction. Furthermore, the versatility of the image processing techniques makes the method suitable for determining myocyte shortening in cells that usually bend or move during contraction. The proposed method can be utilized to evaluate changes in contractile behavior resulting from drug intervention, disease modeling, transgeneity, or other common applications to mammalian cardiocytes.

Figure 1

(a) Original image of enzymatically dissociated adult cardiocyte taken from video depicting contractile activity. Contractile activity was recorded using bright light microscopy, while the cell was in a field stimulated chamber. (b) Smoothed image of the same enzymatically dissociated adult cardiocyte during contractile activity, after applying the edge preserving TV-based image smoothing algorithm.

Figure 2

(a) Segmented image of enzymatically dissociated adult myocyte taken from video depicting contractile activity. (b) Final contour extracted from the segmented image of enzymatically dissociated adult myocyte taken from video depicting contractile activity.

Figure 3

Centroid distance function of the cell shape used in our discussion. The profile of this centroid distance function will be typical in our application.

Figure 4

(a) Two identical cell shapes in which one of them has been translated and rotated with respect to the other. (b) first 30 Fourier descriptors for both shapes for the case of translation, rotation, and starting point invariance.

Figure 5

(a) Two cell shapes in which one of them is larger than the other. (b) first 30 Fourier descriptors superimposed. We observe that their Fourier descriptors are able to capture this change in shape size making the Fourier descriptors variant to scale but invariant to translation, rotation, and starting point. The “contraction” of the shape is 8.15% as measured by the Euclidean distance of the Fourier descriptors.

Figure 6

(a) Contraction record of adult enzymatically dissociated rat myocyte under electrical stimulation, analyzed using proposed image analysis-based contractility measuring method. (b) Contraction record of adult enzymatically dissociated rat myocyte under electrical stimulation, analyzed using edge detection system.

Figure 7

Average of four contractions shown in Figure 6 for both the video-based edge detection system (dashed) and our proposed image analysis-based contractility measuring method (solid). The contractile responses were normalized to fit a desired range. Both records exhibit similar behaviors during the precontraction period, and the contraction to 90% relaxation period, whereas the records show a noticeable difference in the late relaxation period that can be attributed to the two dimensional properties of the proposed image analysis-based contractility measuring method.