Calculation of the left ventricular ejection fraction by gated radionuclide angiography without direct background correction.

The mathematical characteristics of the cardiac background were studied in 50 patients who underwent both gated radionuclide angiography and cardiac catheterization. The background-corrected ejection fraction (BCEF) was calculated in the standard manner using an operator-defined periventricular background region. The "uncorrected" ejection fraction (UEF) was calculated from the uncorrected left ventricular time-activity curve and compared to both the BCEF and the angiographic ejection fraction (AEF), UEF exhibited remarkable linear correlation with both BCEF and AEF. The empirically determined linear regression equation, AEF = 2.18 (UEF) + 0.13, allowed calculation of a radionuclide ejection fraction corresponding to angiographic methods without direct background correction. When measurement of the left ventricular ejection fraction using this linear regression method was tested prospectively in 25 catheterized patients, the radionuclide regression ejection fraction showed excellent linear correlation with AEF (r = 0.85) and minimal inter-observer variability.