Optimizing the method to calculate right ventricular ejection fraction from first-pass data acquired with a multicrystal camera.

BACKGROUND: The advantage of radionuclide angiographic techniques used to measure right ventricular ejection fraction (RVEF) is geometry independence, but the weakness is right atrial (RA) overlap. To minimize the effect of RA counts on right ventricular time activity curve (TAC), two regions of interest (ROI), one drawn for the end-diastolic image and one for the end-systolic image, are used for the calculation of RVEF from equilibrium gated blood pool scans (GBPS) and from gated first-pass studies with an Anger camera. A multicrystal camera offers both temporal separation of the bolus to the right side of the heart and good count statistics; therefore first-pass studies performed on a multicrystal camera theoretically should yield the most accurate measurements of RVEF, but few studies have been performed to validate RVEF against a reliable gold standard. METHODS AND
RESULTS: To develop and validate an accurate method to measure RVEF from multicrystal first-pass data, 25 patients underwent sequential cine-MRI, first-pass radionuclide angiography, and gated equilibrium imaging. Five additional healthy volunteers underwent cine-MRI alone. Right and left ventricular volumes were measured from serial short axis cine-MRI views according to Simpson's rule. Three methods were used to calculate RVEF from first-pass data: a single ROI method, a dual ROI method, and a method in which a single ROI is applied to RA subtracted first-pass dynamic data. Five additional healthy volunteers underwent cine-MRI alone. When right ventricular stroke volume was plotted versus left ventricular stroke volume for the 5 volunteers and the 15 patients without valvular regurgitation, the regression line was not significantly different from the line of identity, supporting the accuracy of cine-MRI to measure RVEF. The RVEF by cine-MRI ranged from 34% to 59%; first-pass RVEF with a single ROI from 26% to 48%; first-pass RVEF with two ROIs from 31% to 59%; first-pass RVEF with RA subtracted single ROI from 29% to 60%; and RVEF from GBPS with multiple ROIs from 28% to 55%. The regressions for all three of the first-pass methods versus cine-MRI were significant (p < 0.01) as was the regression for the equilibrium GBPS versus cine-MRI but the correlation was weaker. The regressions for the 2-ROI method and for the RA subtracted single ROI method were not significantly different from the line of identity, whereas the regressions for both the single ROI method and for equilibrium GBPS were significantly different from the line of identity (p < 0.01).
CONCLUSIONS: Cine-MRI can be used to validate radionuclide algorithms. Of the four radionuclide methods for measuring RVEF that were assessed, the first-pass 2-ROI method and the first-pass RA subtracted single ROI are the most accurate, the first-pass single ROI method underestimates RVEF, and the RVEF values measured from GBPS are less accurate.