Inflammation, Microcalcification, Peripheral arterial disease, Positron emission tomography, Aged, Asymptomatic Diseases, Carotid Arteries, Carotid Artery Diseases, Chi-Square Distribution, Female, Fluorodeoxyglucose F18, Humans, Male, Plaque, Atherosclerotic, Positron Emission Tomography Computed Tomography, Predictive Value of Tests, Prognosis, Radiopharmaceuticals