Early Identification and Diagnosis of BAD-related Stroke

Inclusion Criteria: * Age 18 to 80 years. * Diagnosis of acute ischemic stroke. * Time from symptom onset to enrollment ≤ 1 week; if the onset time is unknown, time from last known well to enrollment ≤ 1 week. * Availability of required baseline clinical and neuroimaging assessments according to the study protocol. * Written informed consent provided by the participant or legally authorized representative. Participants will be classified into the BAD-related stroke cohort if they meet all predefined BAD-related stroke diagnostic criteria, including: * A single isolated deep subcortical infarct on diffusion-weighted imaging. * The presumed culprit perforating artery is the lenticulostriate artery or the paramedian pontine artery. * For lenticulostriate artery territory infarction: a comma-shaped lesion extending from inferior to superior direction on coronal DWI or involvement of ≥3 axial DWI slices with 5-7 mm slice thickness. * For paramedian pontine artery territory infarction: a lesion extending from the deep pons to the ventral surface of the pons on axial DWI. * No ≥50% stenosis of the corresponding parent artery, confirmed by MRA, CTA, or DSA. Participants with acute ischemic stroke who do not meet BAD-related stroke criteria will be classified into the non-BAD acute ischemic stroke cohort. Exclusion Criteria: General exclusion criteria for all participants: * Intracranial hemorrhage, vascular malformation, aneurysm, brain abscess, malignant intracranial mass, or other non-ischemic intracranial lesion on baseline CT, MRI, MRA, CTA, or DSA. * Pre-stroke modified Rankin Scale score ≥2. * Life expectancy ≤6 months. * Unable to tolerate MRI examination. * Pregnancy or breastfeeding. * Participation in another clinical study within 3 months before informed consent or current participation in another clinical study that may interfere with this study. Additional criteria that preclude classification as BAD-related stroke: * Ipsilateral extracranial tandem artery stenosis ≥50%. * Definite cardioembolic source, including atrial fibrillation, myocardial infarction, clinically significant valvular heart disease, dilated cardiomyopathy, infective endocarditis, atrioventricular conduction disease, or heart rate \<50 beats/min as defined in the protocol. * Receipt of or planned acute-phase endovascular treatment after stroke onset. * Stroke due to other determined causes, such as moyamoya disease, arterial dissection, or vasculitis.