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Estimation of right ventricular ejection fraction by means of 99Tcm-macroaggregates.

A method is described for assessing right ventricular ejection fraction (RVEF) by means of 99Tcm-macroaggregates (MAA). The method consists of performing, in right anterior oblique (RAO) projection, a direct ECG-gated data acquisition over 120 s, as soon as the intravenous administration of the tracer is started. The activity returning to the left heart being negligible, background is limited to the lung activity overlapping the right ventricle. The distribution of lung activity in the gated frames is, however, exactly the same as that in the lung perfusion image, it can therefore be subtracted using static lung scintigraphy acquired directly after the gated study. Considering the count density distributions in the corrected end-diastolic (ED) and end-systolic (ES) frames and the first harmonic phase and amplitude images, ED and ES RV regions of interest (ROIs) are delineated for the calculation of RVEF. It has been shown that using 5 mCi 99Tcm-MAA, the ED count obtained is similar to that usually observed during a 20 mCi 99Tcm first-pass study. Intraobserver variation is acceptable and there is a good correlation between the RVEF calculated by this method and that obtained by means of a steady-state ECG-gated 81Krm technique. As the method presents similar advantages to those offered by 81Krm while using 99Tcm, it constitutes, in our opinion, a good approach for estimating RVEF in routine clinical practice.