Nongeometric determination of right ventricular volumes from equilibrium blood pool scans

Abstract

It has previously been shown that left ventricular volumes can be measured accurately from radionuclide gated blood pool scintigrams by quantttating the background-corrected and volume-normalized ventricular activity at end-diastole and end-systole. To determine if this same technique can be applied to the calculation of right ventricular volumes, simultaneous measurements of right ventricular stroke volume were performed using gated scintigraphy and the thermodilution technique in 60 patients without clinical or hemodynamic evidence of right-sided regurgitation. Three techniques for the acquisition of the radionuclide studies were evaluated. The best correlation between scintigraphic and thermodilution determinations of stroke volume was obtained for studies acquired with a 25 ° rotating slant hole collimator positioned in a 10 to 15 ° left anterior oblique projection with the collimator slant directed toward the cardiac apex along the axis of the interventricular septum: Thermodilution stroke volume = 4.2 (scintigraphic stroke volume) + 10.3 ml (correlation coefficient [r] = 0.88; standard error of the estimate = 9.3 ml; probability [p] < 0.0001). This scintigraphic acquisition technique was superior to (1) a straight bore collimator positioned in a septal projection (30 to 50 ° left anterior oblique with 15 ° caudal tilt), and (2) a 25 ° slant hole collimator positioned in a similar septal projection with the collimator slant directed caudally. This method was evaluated prospectively in an additional 14 patients, and there was excellent agreement between stroke volumes obtained with thermodilution and scintigraphic methods (r = 0.96, p < 0.001). In addition, measurements of right ventricular ejection fraction by the equilibrium method agreed closely with those obtained with a gated first pass technique (r = 0.94, p < 0.001, n = 14). With use of the scintigraphic right ventricular ejection fraction and the relation between scintigraphic and thermodilution measurements of right ventricular stroke volume, right ventricular end-diastolic and end-systolic volumes can be estimated. Thus, nongeometric radionuclide techniques may be used for the quantitation of right ventricular volumes.