Accuracy of gated equilibrium radioventriculography in measuring left ventricular function in dogs

To assess the precision of gated equilibrium radioventriculography in measuring changes in left ventricular stroke volume (LVSV), we studied five dogs each with a chronically implanted electromagnetic flowmeter on the ascending aorta. Per cent changes in left ventricular stroke counts (LVSC) were compared to those in LVSV following acute changes induced by positive end respiratory pressure. We have compared LVSCs calculated in five different ways: (1) Manual outlining of LV region of interest (LVROI), either single fixed enddiastolic (ED) ROI or ED and endsystolic (ES) ROIs with the aid of functional images (first harmonic of Fourier analysis); (2-5) automatic outlining of LV ROI (the algorithm generated 30 profiles on which the maximum of second derivative delineated the LV edges) was performed either on ED image or both ED and ES images. For these four methods a crescent-shaped ROI for background correction was manually drawn at the border of the LV ROI. The fifth method used an automatically drawn single fixed LVED ROI with interpolative background substraction (IBS) between LV and RV edges. LVSC changes, calculated with the IBS method correlated better with LVSV changes than the other four methods. Thus assessment of small LVSC changes is highly processing-dependent.