Two dimensional echographic imaging of the left ventricle: comparison of mechanical and phased array systems in vitro.
To determine the reliability of two dimensional echographic images of the left ventricle with different two dimensional echographic instruments, two dimensional echographic images of the left ventricle were compared in vitro using two phased array and two mechanical systems to image 22 short axis slices of the three postmortem human hearts (one with infarction, one with left ventricular aneurysm, one with mitral regurgitation). Total left ventricular area and left ventricular cavity area were determined with planimetry and myocardial area was derived by subtraction. Comparison of total, myocardial and cavity areas with calibrated photographs of each slice showed excellent correlations for each echographic system (r = 0.93 to 0.97 for total area; 0.90 to 0.94 for cavity area; 0.89 to 0.95 for myocardial area). For total left ventricular area, the ratio of echographic to photographic image size was close to unity (0.95 to 1.08) for one mechanical and two phased array systems, but significantly lower for mechanical system 2 (0.71, p less than 0.001). For myocardial area the echographic/photographic ratio was also close to unity (0.96 to 1.15) for two phase array systems and mechanical system 1 but significantly lower for mechanical system 2 (0.77, p less than 0.005). In contrast, all systems underestimated left ventricular cavity area with lower, more variable echographic/photographic ratios (0.48 to 0.78), with mechanical system 2 again giving significantly lower values (p less than 0.02) than the other systems. Underestimation of left ventricular cavity area appears to result from inaccurate endocardial display. We conclude that accurate left ventricular image quantitation is possible with either phased array or mechanical systems if each variable studied is calibrated against an independent reference standard and echographic results are corrected by the resultant regression equation.