5. Subclinical carotid atherosclerosis by carotid ultrasound apparatus Assessment indexes of subclinical atherosclerosis including carotid intima-media thickness (IMT), carotid plaque, carotid internal diameter， carotid blood flow peak velocity, diastolic peak velocity of carotid artery, average velocity, resistance index (RI) and pulsation index (PI) will be measured by Doppler ultrasound apparatus.