3D-ECHOCARDIOGRAPHIC LEFT-VENTRICULAR VOLUME DETERMINATION

2D-echocardiography is a safe and inexpensive method for accurate left ventricular volume quantification. However, accuracy of measurements is limited by the requirement of geometric assumptions and volume computation algorithms. Reproducibility is diminished by erroneous image plane positioning, which is due to the necessity of standardized reference images. The degree of variation can influence clinical decision making. 3D-echocardiography has overcome those problems. Volume quantitation is performed without the need of geometric assumptions, computation algorithms or reference images, The shape of a ventricle is defined by acquired data, not by calculated data. Since the recent development of sophisticated hardware- and software techniques the method can be utilized under clinical circumstances. For data acquisition tomographic planes are acquired either in a random or in a sequential order. For random acquisition the transducer is positioned at various acoustic windows at the thoracic wall and spatial orientation of the corresponding plane is localized by a spark gap device. By this way various: non-parallel cross-sectional images of the left ventricle are acquired. The spatial position of the planes is displayed by lines in a parasternal longitudinal view, each representing a ''line of intersection''. When tomographic planes are acquired in a sequential manner, mostly rotational scanning is utilized, Here, multiple apical views of the left ventricle are acquired during ECG- and respiration gated rotation of the transducer over a span of 180 degrees. After off-line reconstruction of the left ventricle volumes are calculated either by integrating geometric figures with a defined volume in the ventricle, or by building cross-sectional slices, each representing part of the ventricle with its volume calculated by the traced cross-sectional area and the operator defined height of the slice. The reconstructed left ventricle can be displayed as a wire frame diagram or in shaded surface technique. In several in-vitro and animal studies 3-dimensional volume measurements were more accurate and less variable than conventional 2-dimensional measurements. This has been confirmed recently in in-vivo studies at human distorted left ventricles. When the echocardiographic measurements are compared to cineventriculography, a lower degree of underestimation is obtained when 3D-echocardiography is utilized. This is due to the more frequent visualization of excentrically shaped left ventricular pathology and of the apex. The possibility of separate volume determination of excentrically shaped parts of the left ventricular chamber offers new methods in the quantitative assessment of aneurysmatic left ventricles. Furthermore, the degree of underestimation remains small and more constant with increasing cineventriculographic volumes, which is in contrary to 2D-echocardiography. A nearly 2-fold improved reproducibility is obtained by the method when compared to 2D-echocardiography. Image displacement is avoided by the known spatial localization or the automatic visualization of the left ventricular cross-sectional images, in which the border tracings have to be performed. Images are therefore more precisely to reproduce than the 2-dimensional reference images. 2D-echocardiographic volume quantitation is limited by the more time consuming measurement technique and minor resolution problems. Nevertheless, the results from the recent studies imply that left ventricular 3D-volumetry will become the new standard in the quantitative assessment of myocardial function.