Evaluation of cardiac tissue from two-dimensional echocardiogram: analysis of gray level and its distribution

Two-dimensional echocardiograms of parasternal long-axis view were recorded and the mean echo intensity and its distribution in the interventricular septum were examined for the purpose of inferring myocardial tissue. Six healthy subjects (N), 29 with left ventricular hypertrophy (LVH), and 12 with old anteroseptal myocardial infarctions (MI) were used in the study. Settings for gain control were adjusted in the constant manner. Data were recorded on a Video tape recorder, with analog data converted to digital signals, subjected to a low-pass filtering, and then analyzed by a Computer tomography image processor. The region of interest was set within the interventricular septum, and a mean relative echo intensity and its histogram (number of pixels showing different echo intensity) was evaluated. The histogram patterns were examined and the parameter for skewness, which shows asymmetrical characteristics, and the parameter for kurtosis, which shows degree of peakedness of distribution, were calculated. Relative echo intensity was found to increase in the order MI greater than LVH greater than N. Histograms showed the majority of pixels were concentrated at the low echo intensity level in the normal group, while pixels were distributed in a relatively gentle slope around the mean value in the LVH group. Many pixels were in the high intensity levels in the MI group, although the rest were dispersed throughout various intensities including low level. The differences are thought to be related to the extent and density of fibrosis. Analysis of two-dimensional echocardiographic echo intensity and distribution may be useful in characterizing myocardial tissues.