Lisette van Dam

Chapter 13 192 In this thesis, we described studies that aimed to overcome diagnostic challenges in venous thromboembolism (VTE) using novel imaging techniques. Chapter 1 provides a general introduction of the diagnosis of pulmonary embolism (PE) and deep vein thrombosis (DVT) at different anatomic locations and an overview of the presented studies. The diagnostic management of suspected VTE can be complex, especially in certain settings such as in suspected recurrent VTE. An adequate diagnosis in this patientgroup is of great importance because most patients diagnosed with a recurrence are treated with lifelong anticoagulant treatment. In suspected recurrent PE, the YEARS algorithm incorporating 3 clinical items and a D-dimer test with a pre-test probability dependent threshold, followed by computed tomography pulmonary angiography (CTPA) is the current favored diagnostic strategy. Although persistent thrombi can be present after a previous PE, these are hardly relevant in the diagnostic management of suspected recurrent PE. In most patients the PE will completely resolve over time and when persistent thrombi in the pulmonary artery are present these are often of limited size. The diagnostic management in suspected recurrent DVT proves more of a challenge. First, the safety of the commonly used Wells score in combination with a D-dimer test in this setting has not been proven beyond doubt. Second, up to 50% of patients with a previous DVT have persistent thrombi after one year, despite adequate anticoagulant treatment. The differentiation between acute recurrent DVT and chronic residual thrombosis with compression ultrasonography (CUS) is difficult and sometimes impossible. As a result, CUS is not able to provide a definite diagnosis in 30% of patients with suspected recurrent ipsilateral DVT. Magnetic Resonance Non-Contrast Thrombus Imaging (MR-NCTI) is a magnetic resonance imaging (MRI) technique that can directly visualize the metabolism of a fresh thrombus by imaging methemoglobin, which is formed in a fresh blood clot by the oxidation of hemoglobin. This technique can thus be used to differentiate acute from chronic thrombosis and to accurately visualize notorious difficult to image VTE. Magnetic Resonance Direct Thrombus Imaging (MRDTI) is a MR-NCTI sequence that has been shown to accurately diagnosis a first DVT and to differentiate acute from chronic DVT in the legs. Before MRDTI could be implemented in the diagnostic management of suspected recurrent ipsilateral DVT in clinical practice an outcome study needed to be performed. In Chapter 2 , we described the Theia study in which the safety of MRDTI to exclude acute recurrent ipsilateral DVT was assessed. We showed that the 3-month