Lisette van Dam

MRI for diagnosis of recurrent ipsilateral DVT 2 15 INTRODUCTION Despite major technical advances in recent years, critical limitations to current available diagnostic techniques for venous thromboembolism (VTE) exist in specific settings. The failure to provide an accurate diagnosis may lead to misdiagnosis and subsequent mistreatment, affecting both morbidity and mortality. 1,2 One of these settings is suspected recurrent ipsilateral deep vein thrombosis (DVT) of the leg, in which the safety of ruling out recurrent DVT by applying clinical decision scores and D-dimer testing has not been established. 2 Moreover, the diagnosis of recurrent DVT using compression ultrasonography (CUS) is complicated by residual vascular abnormalities following a first DVT episode in up to 50% of patients after one year despite adequate anticoagulant treatment. 3-5 CUS has been proposed to be diagnostic for recurrent DVT in case of a new non-compressible venous segment or a ≥ 2-4 mm increase in vein diameter of a previously non-compressible vein, in comparison with a prior CUS. 6-9 However, in clinical practice a prior CUS is often unavailable and comparisons with previous CUS examinations are subject to major interobserver variability. 10 Similarly, these residual vascular abnormalities complicate the interpretation of all other diagnostic modalities, including contrast venography. As a consequence, recurrent ipsilateral DVT cannot be ruled out in up to 30% of patients in daily practice, resulting in overtreatment. 3 Magnetic resonance direct thrombus imaging (MRDTI) is a technique with a short 10-minute acquisition time that is based on the formation of methemoglobin in a fresh thrombus which appears as a high signal when imaged on a T1 weighted MRI sequence by measurement of the shortening T1 signal. 11 This technique does not require intravenous gadolinium contrast. MRDTI can accurately diagnose a first DVT and distinguish acute recurrent DVT from chronic residual thrombotic abnormalities with a sensitivity and specificity of at least 95%. 12,13 MRDTI therefore has potential to be used as a single test to diagnose or rule out recurrent ipsilateral DVT, but a formal outcome study had not been performed previously. 14 We have conducted a prospective management study to evaluate the safety of ruling out acute recurrent ipsilateral DVT of the leg by a MRDTI negative for DVT.