Lisette van Dam

Magnetic resonance thrombus imaging in portal vein thrombosis 6 97 INTRODUCTION Acute portal vein thrombosis (PVT) has a poor short- and long-term prognosis 1 and a higher mortality rate than the ‘usual site’ venous thromboembolism, i.e. acute pulmonary embolism and deep vein thrombosis (DVT). Therefore, timely diagnosis and anticoagulant treatment are crucial for the patients’ prognosis. 2-4 Distinguishing between a fresh thrombus, in which anticoagulant treatment is indicated, and a chronic (organized, non-resolvable) thrombus is of paramount importance for treatment decision. 5 However, currently available imaging tests are not always able to accurately differentiate acute from chronic PVT, especially when it concerns an organized non-occlusive chronic thrombus without signs of cicatrization of the affected vessel. Magnetic resonance non-contrast thrombus imaging (MR-NCTI), also referred to as Magnetic Resonance Direct Thrombus Imaging (MRDTI) in previous publications, is a non-contrast-enhanced magnetic resonance imaging (MRI) technique which allows for direct visualization of acute thrombi. 6 This technique is based on the formation of methemoglobin in a fresh thrombus which appears as high signal intensity on a T1 weighted MRI sequence by shortening the T1 relaxation time. 6 This increased signal intensity fades when the thrombus ages over a period of 3-6 months. 7 MR-NCTI has been shown to accurately differentiate acute from chronic DVT and to safely exclude acute recurrent ipsilateral DVT of the legs. 7-9 The diagnostic accuracy of MR-NCTI has not yet been evaluated for the diagnosis of PVT. Because imaging of abdominal veins differs in many ways from imaging of veins in the extremities, e.g. artefacts from ascites and intestinal movement and gas, the MR-NCTI sequences used in the extremities need to be adjusted for optimal visualization of PVT. We set out to select and optimize MR-NCTI sequences for differentiation between acute and chronic portal vein thrombosis. MATERIAL & METHODS This study is the first phase of the Rhea study (NTR 7061), a prospective diagnostic study to evaluate the diagnostic accuracy of MR-NCTI for distinguishing acute from chronic PVT. In the Rhea study our aim is to include 70 PVT patients, including 35 patients with confirmed acute PVT (partial or occlusive), i.e. acute symptoms ( < 2 weeks) characteristic for PVT, diagnosed with doppler ultrasound (Doppler US),