Summary.  Background: Accurate diagnosis of acute recurrent deep vein thrombosis (DVT) is relevant to avoid improper diagnosis and unnecessary life‐long anticoagulant treatment. Compression ultrasound has high accuracy for a first episode of DVT, but is often unreliable in suspected recurrent disease. Magnetic resonance direct thrombus imaging (MR DTI) has been shown to accurately detect acute DVT. The purpose of this prospective study was to determine the MR signal change during 6 months follow‐up in patients with acute DVT. Patients/methods: This study was a prospective study of 43 consecutive patients with a first episode of acute DVT demonstrated by compression ultrasound. All patients underwent MR DTI. Follow‐up was performed with MR‐DTI and compression ultrasound at 3 and 6 months respectively. All data were coded, stored and assessed by two blinded observers. Results: MR direct thrombus imaging identified acute DVT in 41 of 43 patients (sensitivity 95%). There was no abnormal MR‐signal in controls, or in the contralateral extremity of patients with DVT (specificity 100%). In none of the 39 patients available at 6 months follow‐up was the abnormal MR‐signal at the initial acute DVT observed, whereas in 12 of these patients (30.8%) compression ultrasound was still abnormal. Conclusion: Magnetic resonance direct thrombus imaging normalizes over a period of 6 months in all patients with diagnosed DVT, while compression ultrasound remains abnormal in a third of these patients. MR‐DTI may potentially allow for accurate detection in patients with acute suspected recurrent DVT, and this should be studied prospectively.

Key Points• Diagnostic management of ipsilateral recurrent DVT of the leg is complicated because residual DVT is common and mimics acute DVT on CUS.• MRDTI is able to reproducibly distinguish acute ipsilateral recurrent DVT from 6-monthold chronic residual thrombi in the leg veins.Accurate diagnostic assessment of suspected ipsilateral recurrent deep vein thrombosis (DVT) is a major clinical challenge because differentiating between acute recurrent thrombosis and residual thrombosis is difficult with compression ultrasonography (CUS). We evaluated noninvasive magnetic resonance direct thrombus imaging (MRDTI) in a prospective study of 39 patients with symptomatic recurrent ipsilateral DVT (incompressibility of a different proximal venous segment than at the prior DVT) and 42 asymptomatic patients with at least 6-month-old chronic residual thrombi and normal D-dimer levels. All patients were subjected to MRDTI. MRDTI images were judged by 2 independent radiologists blinded for the presence of acute DVT and a third in case of disagreement. The sensitivity, specificity, and interobserver reliability of MRDTI were determined. MRDTI demonstrated acute recurrent ipsilateral DVT in 37 of 39 patients and was normal in all 42 patients without symptomatic recurrent disease for a sensitivity of 95% (95% CI, 83% to 99%) and a specificity of 100% (95% CI, 92% to 100%). Interobserver agreement was excellent (k 5 0.98). MRDTI images were adequate for interpretation in 95% of the cases. MRDTI is a sensitive and reproducible method for distinguishing acute ipsilateral recurrent DVT from 6-month-old chronic residual thrombi in the leg veins. (Blood. 2014;124(4):623-627)

SummaryDeep vein thrombosis (DVT) is a common disease that may lead to potentially fatal complications, such as pulmonary embolism. In the past decades several diagnostic tools and algorithms for DVT have been studied. Currently the combination of a clinical decision rule, D-dimer testing and compression ultrasonography has proved to be safe and effective for the diagnosis of DVT in the lower extremities. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) can be useful as additional or secondary imaging modalities. This review will discuss the elements currently used in making the clinical diagnosis of DVT. These elements include clinical decision rules and D-dimer testing, different imaging investigations and the appropriate use of these within diagnostic algorithms in patients with clinically suspected DVT. Although current knowledge of the options available to diagnose DVT of the lower extremities is well established, there are still unresolved issues, including the optimal diagnosis of recurrent DVT and distal DVT. Furthermore, the diagnosis of DVT of the upper extremities will be discussed, including the different imaging modalities and the limitations of these techniques.

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The diagnosis of recurrent ipsilateral deep vein thrombosis (DVT) is challenging, because persistent intravascular abnormalities after previous DVT often hinder a diagnosis by compression ultrasonography. Magnetic resonance direct thrombus imaging (MRDTI), a technique without intravenous contrast and with a 10-minute acquisition time, has been shown to accurately distinguish acute recurrent DVT from chronic thrombotic remains. We have evaluated the safety of MRDTI as the sole test for excluding recurrent ipsilateral DVT. The Theia Study was a prospective, international, multicenter, diagnostic management study involving patients with clinically suspected acute recurrent ipsilateral DVT. Treatment of the patients was managed according to the result of the MRDTI, performed within 24 hours of study inclusion. The primary outcome was the 3-month incidence of venous thromboembolism (VTE) after a MRDTI negative for DVT. The secondary outcome was the interobserver agreement on the MRDTI readings. An independent committee adjudicated all end points. Three hundred five patients were included. The baseline prevalence of recurrent DVT was 38%; superficial thrombophlebitis was diagnosed in 4.6%. The primary outcome occurred in 2 of 119 (1.7%; 95% confidence interval [CI], 0.20-5.9) patients with MRDTI negative for DVT and thrombophlebitis, who were not treated with any anticoagulant during follow-up; neither of these recurrences was fatal. The incidence of recurrent VTE in all patients with MRDTI negative for DVT was 1.1% (95% CI, 0.13%-3.8%). The agreement between initial local and post hoc central reading of the MRDTI images was excellent (κ statistic, 0.91). The incidence of VTE recurrence after negative MRDTI was low, and MRDTI proved to be a feasible and reproducible diagnostic test. This trial was registered at www.clinicaltrials.gov as #NCT02262052.