Disproportionate effects of regional hypokinesis on radionuclide ejection fraction: compensation using attenuation-corrected ventricular volumes.

This study evaluates the potential effects of regional hypokinesis on measurements of global ejection fraction (EF) as determined by radionuclide angiographic techniques. Studies were performed in a two-compartment left-ventricular (LV) model that allowed stimulation of global, anterior-region, or posterior-region hypokinesis in a torso chamber with heart-to-background activity similar to that in clinical studies. Radionuclide techniques accurately measured changes in EF during global hypokinesis but progressively underestimated true EF during increasing anterior-region hypokinesis, and progressively overestimated true EF during increasing posterior hypokinesis. When EF (y-axis) was plotted against true EF (x-axis) for a 240-ml model, from linear regression equations, the slopes and intercepts were significantly different for anterior and posterior hypokinesis. The disproportionate effects of regional hypokinesis increased with LV size. Accurate EF was computed during regional hypokinesis by determining absolute LV volumes from count rates corrected for attenuation, depth, background activity and blood-pool activity. Thus, the disproportionate effects of regional hypokinesis on EF were corrected by considering differential count attenuation.