Venothromboembolic disease (VTE), which includes deep venous thrombosis (DVT) and pulmonary embolism (PE), is a severe health problem, effecting 1.5/1000 per year in the general population. In patients over 60 years of age, the incidence is 1/100 per year. Of the two million Americans per year who will develop VTE, one third will develop pulmonary embolism (PE). VTE is usually diagnosed by Doppler ultrasound or contrast venography when present in the extremities, VQ scan or pulmonary angiography when PE is present. However, there are many instances when the diagnosis of VTE by conventional modalities is limited. These include obesity, recent trauma or surgery, the presence of a mass, the presence of clot around central lines, and clot occurring in the abdomen and pelvis. Furthermore, the differentiation between new and old clot has evaded all diagnostic imaging modalities, and no existing modality allows for an accurate delineation of all sites of thrombus within the body. New approaches to the diagnostic imaging of VTE in complicated cases are needed. The first hypothesis of this project is that FDG PET/CT can be used to accurately diagnose the presence and extent of acute VTE, and that it will distinguish new clot from old.