Patients with moderate aortic stenosis are enrolled and underwent baseline evaluation including 18F-sodium fluoride PET/CT. After 1 year, all the participants underwent follow-up echocardiography. The study design is an observational trial. Primary endpoint was a change in mean pressure gradient along the aortic valve as assessed by echocardiography at 1 year. Secondary endpoints include changes in aortic valve area, and symptom occurrence.