In small studies with helical CT, the ratio of the right ventricle to left ventricle short axis diameters (RV/LV) has been proposed as an accurate sign for the presence of RVD (16-19). In addition, other criteria have been proposed, including deviation of the interventricular septum and the ratio of the pulmonary artery to ascending aorta diameters. Also, the extent of PE (ie, thrombus burden in the pulmonary arteries) has been proposed as an important parameter for predicting RVD (20-21). In a recent retrospective study in 120 patients with pulmonary embolism, seven patients died of PE. Both the RV/LV ratio and the obstruction index were shown to be significant risk factors for 3-month mortality (p = 0.04 and 0.01, respectively). No such relationship was found for the ratio of the pulmonary artery to ascending aorta diameters (p= 0.66) or for the shape of the interventricular septum (p = 0.20). The positive predictive value for PE-related mortality with an RV/LV ratio greater than 1.0 was 10.1% (95% confidence interval [CI]: 2.9%, 17.4%). The negative predictive value for an uneventful outcome with an RV/LV ratio of 1.0 or less was 100% (95% CI: 94.3%, 100%). There was a 11.2-fold increased risk of dying of PE for patients with an obstruction index of 40% or higher (95% CI: 1.3, 93.6). The CT obstruction index (29% ± 17%) and the Miller index (43% ± 25%) were well correlated (r = 0.867, p < 0.0001) with an excellent concordance between investigators for both the CT index (r = 0.944, p < 0.0001) and the Miller index (r = 0.904, p < 0.0001). A CT obstruction index greater than 40% identified more than 90% of patients with right ventricular dilatation.