The aim of our study is to analyze and quantitate whole-body blood perfusion by total-body 13N-NH3 PET/CT(uEXPLORER), and evaluate the influence to other organs in severe AS patients and the impact of TAVR surgery.

Participants are invited to participate in a research that seeks to understand the dynamic blood perfusion in severe AS patients in human body. The investigators expect to have twenty-five participants in this study at Renji Hospital, Shanghai. Nine participants will be healthy individuals with no known vascular disease. All the participants will undergo the same procedure. If participants agree to participate in this study, researchers will first interview participants and review the past medical record in order to document the medical history. When the screening procedures confirm that participants are eligible to participate in the study, participants will receive one dose of the non-therapeutic administration of a radioactive tracer called N-13 ammonia(13NH3) , then undergo one total body 13NH3 PET/CT Scan (uEXPLORER) to determine the blood flow value of the brain, kidney and other organs. The total body 13NH3 PET/CT Scan will allow investigators to observe and analyze the real-time blood flow differences between patients with between healthy controls and decreased cardiac function.

Inclusion Criteria:

• Nine healthy volunteers with normal EF values
• Patients with decreased cardiac function, while their heart function grading above II(New York Heart Association,NYHA)
• Aged 60~90 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 60 years old
• Heart function grading below II(NYHA)
• inability to lie or to maintain posture in the scanner for one hour

Individuals aged between 60 and 90 years old with severe AS condition will be eligible for our enrollment; and participants without any history of vascular disease will be eligible.