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Background: Right ventricular (RV) function is an important parameter in acute pulmonary embolism (PE), both for the choice of therapy, and for the prognosis. The relationship between RV function and the extent of vascular obstruction has been studied by several investigators with contradictory results. The aim of this study was, therefore, to examine the association between the extent of perfusion loss and the RV function, and to introduce a new quantitative method for determining lung perfusion.Methods: RV function was studied in 15 patients with acute PE and with preserved systemic arterial pressure by echocardiography, including pulsed-wave Doppler tissue imaging (DTI) within 24 hours after arrival at the hospital, and compared with the extent of perfusion loss seen in lung scintigraphy, including a new expression of perfusion inhomogeneity.Results. Lung perfusion correlated with pulmonary vascular resistance (PVR, R= -0.86, P=0.03), RV-pressure (R= -0.68, P=0.03), the RV to left ventricular (LV) end-diastolic diameter ratio (RV/LV, R= -0.55, P=0.04) and the early diastolic tricuspid annular velocity (tricuspid Em, R=0.62, P=0.02). Maximal count intensity values correlated with the RV/LV ratio (R=0.76, P=0.002) and tricuspid Em (R= -0.57, P=0.03). Compared to patients with a loss of perfused lung area < 10 %, patients with a loss of perfused lung area ≥ 10 % had a lower systolic tricuspid annular velocity (tricuspid Sm, 12.2 ± 3.7 cm/s vs. 17.0 ± 4.4 cm/s, P=0.01), a lower tricuspid Em (10.1 ± 3.7 cm/s vs. 16.0 ± 4.3 cm/s, P=0.02), and a lower tricuspid annular plane systolic excursion (TAPSE, 17.3 ± 4.0 mm vs. 22.7 ± 4.8 mm, P=0.04). There was a good correlation between the new, maximum count intensity-based method, and the area-based perfusion scan (R= -0.95, P<0.01).Conclusions: The lung perfusion in this study showed a fairly good correlation with pulmonary vascular resistance, RV-pressure and the RV/LV ratio. In patients with preserved systemic arterial pressure, signs of RV dysfunction may already occur at a perfusion loss of ≥ 10 % lung scan area. The degree of inhomogeneous perfusion appears to be well reflected by the maximal count intensity observed in the lung scan.