The Theia-study is a prospective, multicenter, single-arm management (cohort) study.

Consecutive patients with clinically suspected acute, recurrent, ipsilateral, proximal deep vein thrombosis (DVT) of the leg, who fulfil all the inclusion criteria and meet none of the exclusion criteria, are eligible for inclusion and will be managed according to the result of a magnetic resonance direct thrombus imaging (MRDTI) of the affected leg. The MRDTI is to be performed and adjudicated within 24 hours of study inclusion. The final treatment decision will be made based on this ruling of the MRDTI. In case of a positive MRDTI signal, patients will be treated with therapeutically dosed anticoagulants or modified in patients with a recurrent DVT on anticoagulant therapy. Patients with a negative MRDTI ruling will be left untreated, or treatment will be remained unadjusted if they are on anticoagulant treatment at inclusion. All patients with negative MRDTI will be subjected to a standardized compression ultrasonography (CUS) within 48 hours after initial presentation. The latter CUS serves as a reference test in case the patient returns with symptoms of ipsilateral recurrence in the future, and will not be used for management decisions at baseline. The study flowchart can be found in Appendix A.

All patients will be followed for three months for the occurrence of acute recurrent venous thrombo-embolism (VTE). In case of suspected recurrent VTE, objective testing including either computed tomography pulmonary angiography (CTPA) for PE or CUS for DVT will be performed. Additionally, in case of a proven ipsilateral recurrent DVT during follow-up, MRDTI will be repeated.

See below.

Inclusion Criteria:

1. Ability of subject to understand the character and individual consequences of this study;
2. Signed and dated informed consent of the subject available before the start of any specific study procedures;
3. Age ≥18 years;
4. Suspected acute recurrent ipsilateral DVT, as defined by a documented prior objectivated episode of DVT in the same leg as current symptoms originate from

Exclusion Criteria:

1. General contraindications for MRI: claustrophobia, pregnancy, intracranial vascular clips, any ferromagnetic implants, presence of a cardiac pacemaker or defibrillator, metallic splinters in the eye, any trauma or surgery which may have left ferromagnetic material in the body;
2. CUS-proven acute symptomatic DVT within 6 months before current presentation;
3. Onset of symptoms suggestive of acute recurrent DVT more than 10 days prior to presentation;
4. Suspected acute PE;
5. Hemodynamic instability at presentation (as a consequence of concurrent acute PE or otherwise);
6. Medical or psychological condition that would not permit completion of the study or signing of informed consent, including life expectancy less than 3 months, or unwillingness to sign informed consent;
7. Non-compliance or inability to adhere to treatment or follow-up visits.
8. Patients with suspected acute, recurrent, ipsilateral DVT on therapeutic anticoagulant treatment > 48 hours at inclusion*

Note: *From August 2015 onward, patients with suspected acute, recurrent, ipsilateral DVT on anticoagulant treatment were allowed in the study as they were found to represent a high proportion (30%) of the screened study population.