Inclusion Criteria:  Three healthy volunteers with normal EF values Four patients with moderate or mild decreased EF values, while their heart function grading above II(New York Heart Association,NYHA) Nine patients with aortic stenosis Aged 18~75 years old Written informed consents will be offered and signed by all participants  Exclusion Criteria:  History of vascular-related diseases in other organs Severe liver and kidney dysfunctions Patients who are pregnant or breast feeding People under the age of 18 years old Heart function grading below II(NYHA) inability to lie or to maintain posture in the scanner for one hour