10-20% of patients with subarachnoid hemorrhage die before they arrive at the hospital, and about 25% die within 24 hours. About 1% of patients are diagnosed with cerebral aneurysms in imaging tests for health checkups, and many of them experience aneurysmal rupture during their lifetime, so it is not a rare disease. Wall shear stress is known to be a factor that reflects the state of blood vessels, and particularly plays an important role in the patency of the intima of blood vessels. In the meantime, computed fluid dynamics (CFD), a representative method for calculating wall shear stress, assumes a virtual rigid pipe and applies a preset value. This does not accurately reflect the physiological and dynamic state of the actual blood vessel. The investigators intend to measure the patient's wall shear stress using the SIG of the MRA-TOF technique, which reflects the physiological characteristics of individual patients, and to analyze the association with rupture of the intracranial aneurysm.

<Ruptured group>

Inclusion Criteria:

1) Patients over 18 years of age who visited our hospital for acute subarachnoid hemorrhage due to rupture of a intracranial aneurysm (2) Among patients satisfying (1), who had intracranial magnetic resonance imaging (time-of-flight (TOF) technique applied; diffusion-weighted imaging, including apparent diffusion coefficient) before subarachnoid hemorrhage occurred.

Exclusion Criteria:

1. Patients under the age of 18
2. Patients with subarachnoid hemorrhage due to causes other than rupture of intracranial aneurysm
3. Patients with poor imaging quality due to artifacts caused by patient movement during brain magnetic resonance imaging examination

<Unruptured group>

Inclusion Criteria:

1. Magnetic resonance imaging performed during the screening period (Time-of-Flight (TOF) technique is applied to intracranial vessel imaging; It also includes diffusion-weighted imaging and apparent diffusion coefficient)
2. Patients diagnosed with unruptured intracranial aneurysm in the final reading of brain MR test
3. Patients who remain without aneurysmal rupture on follow-up intracranial magnetic resonance imaging

Exclusion Criteria:

1. Patients under the age of 18
2. Patients with poor imaging quality due to artifacts caused by patient movement during brain magnetic resonance imaging examination

Patients visited health checkup program or neurology clinic (unruptured group), or emergency department (ruptured group) of a tertiary center