Inclusion Criteria- Patient over 18
- Patient having a CHADS-VAsc Score ≥ 2;
- Patient hospitalized for a secondary established ischemic accident in an atrial fibrillation not anticoagulated (INR<2 and/or receiving antiplatelet (aspirin, clopidogrel)) for less than 14 days;
- Patient affiliated to a national insurance scheme or beneficiary
- Patient having given a written consent
Exclusion Criteria- Patient presenting cognitive disorders incompatible with the planned examinations (MRI / SCANNER).
- Pacemaker or implantable defibrillator, or other contraindication in the MRI (metallic eye brightness, intra cerebral clip).
- Contraindication in injected scanner.
- Current pregnancy