[18F]FLUORIDE PET-CT

This study will evaluate the two main types of replacement tissue heart valve used in current practice, comparing outcomes from surgical aortic valve replacement (AVR) with that of the more recently introduced "key-hole" procedure called transcatheter aortic valve implantation (TAVI). Participants will be recruited at various time points ranging from 1 month to 10 years following valve replacement with either AVR or TAVI. It is thought that progressive calcium (chalk) formation is responsible for the failure of the majority of these valves. All participants will therefore have a PET-CT scan with a special type of "tracer" called 18F-fluoride in order to measure active calcium formation in the valve. They will then have annual clinical follow-up for 5 years and be invited back for a repeat CT scan at 2 years to measure change in calcium burden. This study aims to investigate, firstly, the effects of valve age and type on calcium formation as measured by PET-CT and, secondly, whether this measure of calcium formation can help to predict how long different types of valve will last. If successful, 18F-fluoride PET-CT could become a valuable tool for testing new treatments to improve valve longevity and new valve designs.