Harmonic subtraction for evaluating right ventricle ejection fraction from planar equilibrium radionuclide angiography

We report an initial investigation of a subtraction-based method to estimate right ventricle ejection fraction (RVEF) from ECG-gated planar equilibrium radionuclide angiography (ERNA) data. Twenty-six consecutive patients referred for scintigraphic evaluation of cardiac function prior to chemotherapy had ECG-gated first-pass (FP) imaging and ERNA imaging performed following the same radiotracer injection. RVEF was computed from FP images (RVEF_FP) and separately from ERNA images (RVEF_ERNA). Standard methods for computing ejection fractions were used to obtain RVEF_FP values. RVEF_ERNA values were obtained using harmonic subtraction of the left ventricular contribution from a biventricular region of interest contoured on the equilibrium images acquired in the shallow right anterior oblique projection. Clinically acquired chest CT data were used to derive information regarding the relative position of the left and right ventricle and about the presence of pulmonary artery enlargement. Computation of RVEF_ERNA was successful for each of the 26 patients. Computation of RVEF_FP failed for four patients. For the 22 patients for which RVEF was computed using both methods, the average RVEF_FP was 49% and the average RVEF_ERNA was 51%, with coefficients of variation of 11 and 7.5%, respectively. Low RVEF_ERNA values were associated with pulmonary artery dilation. Estimation of RVEF_ERNA, using a harmonic subtraction-based method of computation is clinically feasible and accurate in the patient population studied. The results support further investigation in patients with frank heart failure.