Inclusion Criteria:  Be aged 18 or over, male or non-pregnant female; Patients have a unruptured vertebrobasilar dissecting aneurysm identified on imaging (CT, MRI or DSA) Patients with wall enhancement and intramural hematomas of UVBDAs by HR-VW-MRI before treatment. Patients who is able to understand the objective of the trail, agrees and signs the written informed consent form.  Exclusion Criteria:  The aneurysm types of non-dissecting aneurysm, such as saccular aneurysms, fusiform aneurysms and traumatic aneurysms, etc.; Patients with MRI contraindications: metallic implant, contrast allergy, claustrophobia, etc.; Planned treatment of the aneurysm within 6 months; Several impaired liver or renal functions; Retreatment of recurrent aneurysm; Pregnant or lactating women; Patients with malignant diseases, such as liver disease, kidney diseases, congestive heart failure, malignant tumors, etc.; Poor compliance patients;