[Automatic and semiautomatic contour finding of the left ventricle in the 2 dimensional echocardiogram. In vitro studies in formalin-fixed swine hearts].

In order to test semiautomatic and automatic contour finding procedures in 2-dimensional echocardiograms we determined endocardial borders in 42 short-axis slices of post-mortem animal hearts after interactive image enhancement such as scaling, normalisation and linearisation of grey levels semiautomatically and automatically by a complex contour finding algorithm. The areas calculated on the basis of these semiautomatic and automatic procedures were compared with "true" anatomic areas derived from planimetry. The complex computer algorithm is based on the detection and analysis of grey level gradients. The algorithm first creates a raw contour which still contains intra- and extracavitary artefacts as well as interrupted endocardial strings. Using a statistical iterative classification procedure and a least-square polynomial approximation the endocardial strings were structured, completed and smoothed and the artefacts eliminated. We were able to determine endocardial contours by semiautomatic methods in 33 (79%) and by automatic procedures in 30 (73%) of the echocardiograms. The correlation between semiautomatic and "true" contours was r = 0.97; y = 1.01x-0.46; standard error of the estimate (SEE) 0.51 cm2, between automatic and "true" contours r = 0.98; y = 0.99x - 0.31; SEE 0.43 cm2; the correlation parameters between the anatomic "true" areas and the areas calculated on the basis of manually derived borders were r = 0.98; y = 0.97x - 0.05; SEE 0.45 cm2. From our studies we conclude that left ventricular endocardium in short axis slices of postmortem animal hearts could reliably and reproducibly be detected by semiautomatic as well as by automatic procedures using a contour finding algorithm.