 First-generation hCTs were based on a single-detector technique and had a limited 70 sensitivity. Moreover, in two recent outcome studies, a proximal deep venous thrombosis diagnosed by lower limb compression ultrasonography was found in 15 of patients with a normal single-detector hCT. However, in management studies, the association of a normal lower limb compression ultrasonography and a normal single-detector hCT has been proved safe to rule out PE in patients with a non-high clinical probability, with a less than 2 rate of thromboembolic events during a 3-month follow-up in patients left untreated based on that combination. Hence, lower limb compression ultrasonography must be combined with a single-detector CT to safely rule out pulmonary embolism. 