As the population increases and aging intensifies, cognitive disorders represented by Alzheimer's disease (AD) not only pose a severe threat to public health but also bring significant social and economic burdens. Previously, treatment options for Alzheimer's disease were very limited, mainly providing symptomatic relief with few available medications. Lecanemab, an FDA-approved clinical treatment drug in 2023, targets the core pathology of AD-abnormal amyloid-beta (Aβ) aggregation in the brain-and has been validated through both biomarker and clinical scale assessments. The optimal dosage and safety-efficacy profile of lecanemab for treating early AD have been observed in phase 2 and phase 3 clinical trials. However, the use of lecanemab may lead to certain adverse effects, including infusion-related reactions, amyloid-related imaging abnormalities (ARIA), such as microhemorrhages or hemosiderin deposits (ARIA-H), and ARIA-E. This study aims to establish a prospective follow-up cohort of patients treated with lecanemab to observe changes in cranial imaging characteristics and clinical symptoms, assess the cognitive improvement effects of lecanemab in early AD patients (stages 3-4), and monitor the risk factors for adverse event occurrence.