Identification the Cause of Silent Cerebral infarctiON in Healthy Subjects (ICONS)

Inclusion Criteria: Healthy subjects * Subjects with age over 20 years * Subjects who consecutively visited a health promotion center for a health screening examination that included routine laboratory test, cardiac work-ups (12-lead electrocardiography and/or echocardiography), and brain magnetic resonance image (MRI) and MR angiography (MRA) * Subjects who showed silent brain infarction (SCI) which was defined as a focal hyperintensity lesion 3 mm or large in diameter in the fluid-attenuation inversion recovery (FLAIR) images without a history of a corresponding stroke or transient ischemic attack (TIA) * Subjects who performed agitated saline transcranial Doppler (TCD) monitoring Patients with acute stroke (both cryptogenic embolic stroke and conventional stroke mechanisms) * Patients with age over 20 year * Patients with focal neurologic deficits presented within 7 days of symptom onset * Patients with acute ischemic lesions on diffusion-weighted image (DWI) * Patients who performed agitated saline TCD monitoring Exclusion Criteria: Healthy subjects * Subjects with the presence of previous history of stroke or TIA * Subjects with the presence of dementia on history taking or mini-mental status examination * Subjects with the presence of proximal source of embolism, including atrial fibrillation or significant (≥50%) stenosis on cervicocerebral artery on MRA or carotid Duplex * Subjects who had SCI restricted within perforator territory (basal ganglia or pons) suggesting that microangiopathy rather than embolism could be the main mechanism of SCI * Subjects in whom agitated saline TCD monitoring was not performed or those who had poor temporal windows Patients with acute stroke (both cryptogenic embolic stroke and conventional stroke mechanisms) * Patients in whom agitated saline TCD monitoring was not performed or those who had poor temporal windows