TSPO and Alzheimer disease: We will examine the effects of semaglutide compared with placebo on brain neuroinflammation as determined by the Translocator Protein 18 kDa (TSPO) PET and plasma assays of biomarkers relevant to dementia, cognition, neurodegeneration as determined by MRI, AD plasma biomarkers and physical activity variation as determined by wrist-worn actigraphy.