Segmentation of the Left Ventricle

Abstract

As with all methods of cardiac imaging, from ventriculography to scintigraphy, the left ventricle can be subdivided into a series of slices or segments also for the purposes of echocardiographic examination. The resolution of the segmental approach is a function of the number of segments; thus it can range from 20% (in the 5-segment model) to 5% (in the 20-segment model). However, increasing the number of segments, and thus reducing their size, leads to an unacceptable complication of the analysis with a greater need for approximation and interpolation. A reasonable trade-off between accuracy and feasibility is represented by the 16-segment model proposed by the American Society of Echocardiography [1], recently modified to include the 17th segment, i.e., the true apex [2]. The wall segments are identified according to internal anatomical landmarks of the left ventricle, in the standard parasternal (long axis and short axis at the mitral, papillary, and apical levels), apical (5-, 4-, 3-, and 2-chamber) and subcostal (long axis and short axis) views (Fig.3). Each segment can usually be visualized in more than one echocardiographic section and from different approaches for a more reliable and complete evaluation of wall motion. As a rule, segmental wall motion can be safely assessed when the endocardial contour is clearly visualized for at least 50% of its length. The 17-segment model meets the basic requirements of any reasonable segmentation: it is simple enough to be employed in practice, it has an anatomical basis, segments can be easily identified on the basis of obvious echocardiographic landmarks, there is good correspondence with the distribution of coronary arteries, and the model has stood the test of multicenter cooperative studies [3].