Lisette van Dam

Chapter 1 8 Venous thromboembolism (VTE) encompasses pulmonary embolism (PE) and deep vein thrombosis (DVT). DVT most commonly occurs in the deep veins of the lower extremity but can also occur in the veins of upper extremity, abdomen and cerebrum. As symptoms of VTE are nonspecific, the diagnosis of VTE is based on diagnostic tests, including clinical decision rules (CDR), D-dimer tests and imaging. Although the diagnostic management of VTE has greatly advanced in recent years with the introduction of novel CDRs and high-sensitive D-dimer tests, the diagnosis may still be challenging in certain settings. The latter is mainly caused by the indirect way of thrombus visualisation by current imaging tests, such as by showing incompressibility with compression ultrasonography (CUS) or a filling defect on contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI). This thesis focuses on challenging settings for diagnosing VTE. One of these settings is suspected recurrent VTE. CUS is the current imaging test of choice in both patients with suspected first and recurrent DVT. 1 However, in suspected recurrent ipsilateral DVT the diagnosis with CUS is complicated as persistent vascular abnormalities after a previous DVT are present in up to 50% of patients after one year. 2 Magnetic Resonance Non-Contrast Thrombus Imaging (MR-NCTI) is a non-invasive MRI technique that can directly visualize thrombosis and may be of value in the diagnostic management of recurrent VTE. MR-NCTI is based on the formation methemoglobin when blood clots, resulting in shortening of the MR signal on a T1-weighted MRI sequence. Therefore, acute thrombi are visible as a ‘white’ signal, which disappears when a thrombus is formed ( Figure 1 ). 3,4 Magnetic Resonance Direct Thrombus Imaging (MRDTI), a MR-NCTI sequence, has previously been shown to accurately distinguish acute recurrent DVT from chronic thrombotic remains. 5 Its safety to exclude acute recurrent ipsilateral DVT was evaluated in the Theia study. Results of this prospective multicentre diagnostic management study are described in Chapter 2 . Since it is unknown whether the application of MRDTI in the diagnostic management of suspected recurrent ipsilateral DVT is costeffective, an analysis to compare the one-year healthcare costs between 10 diagnostic scenarios with and without MRDTI was performed. The results are described in Chapter 3 . The combination of a CDR and D-dimer test is used to exclude a first episode of DVT without performing imaging tests. The diagnostic performance of a CDR combined with a D-dimer test has not yet been sufficiently evaluated in patients with suspected recurrent DVT. 6 One of the predefined secondary outcomes of the Theia study was to assess the diagnostic accuracy of the combination of the Wells rule for DVT and a D-dimer test for suspected recurrent ipsilateral DVT ( Chapter 4 ).