Fully automatic segmentation of left ventricular myocardium in real-time three-dimensional echocardiography

摘要

Purpose: We report a deformable model (DM)-based fully automatic segmentation of the left ventricular (LV) myocardium (endocardium + epicardium) in real-time three-dimensional (3D) echocardiography. Methods: Initialization of the DM is performed through automated mutual information-based registration of the image to be segmented with a 3D template (image + corresponding endo-epicardial wiremesh). The initialized endocardial and epicardial wiremesh templates are then simultaneously refined iteratively under the joint influence of mesh-derived internal forces, image-derived external (gradient vector flow-based) forces, and endo-epicardium mesh-interaction forces. Incorporation of adaptive mesh-interaction forces into the DM refinement, a novelty of the current work, ensures appropriate relative endo-epicardial orientation during simultaneous refinement. Repeating for the entire cardiac sequence provides the segmented myocardium for all phases. Preliminary comparison is presented between automatic and expert-defined myocardial segmentation for five subjects imaged in clinical settings using a Philips SONOS 7500 scanner. Results: Root mean square (rms) radial distance error between the algorithm-determined and expert-traced endocardial and epicardial contours in six predetermined planar views was 3.86 ± 0.72 mm and 4.0 ± 0.63 mm in end-diastole, 3.9 ± 0.51 mm and 4.04 ± 0.65 mm in systole, respectively. Mean absolute error between average myocardial thickness calculated using automatic and expert-defined contours was 1.64 ± 0.56 mm (apical), 1.3 ± 0.58 mm (mid) and 1.46 ± 0.45 mm (basal). The absolute difference in ejection fraction calculated using our algorithm and by the expert using the TomTec software was 7.2 ± 0.84 %. Conclusion: We demonstrate successful segmentation of LV myocardium, which allows clinically important LV structure and function (e.g. wall thickness, LV volume and ejection fraction) to be tracked over the entire cardiac cycle.