18F-GP1 binds with high affinity to the glycoprotein IIb/IIIa receptors on activated platelets. 18F-GP1 PET-CT has recently demonstrated favourable safety, pharmacokinetic, biodistribution and diagnostic performance for the in vivo identification of venous and arterial thrombemboli.

Aortic stenosis is the most common reason for valvular interventions in the developed world, with rates projected to increase as the population ages. Aortic valve replacement remains the only recognised treatment available. Bioprostheses are far more common than mechanical prostheses, particularly with increasing rates of transcatheter heart valve use.

Bioprothetic valves are less durable than mechanical valves and are subject to deterioration which may lead to clinical heart failure and the need for re-intervention. Long-term results with surgical bioprostheses are well reported, with valve deterioration rates of less than 15% at 10 years. These data, however, rely on re-operation rather than echocardiographic measures, suggesting that the true incidence of structural valve deterioration is underestimated.

Valve thrombosis is increasingly recognised as a potential contributor to leaflet degeneration and has been detected in participants undergoing both surgical aortic valve replacement and transcatheter aortic valve implantation. The role of valve thrombosis as an early trigger for calcification and subsequent valve degeneration has not been addressed. The true incidence of valve thrombosis and its impact on clinical outcomes is unknown due to the lack of a sufficiently sensitive non-invasive imaging modality to detect early subclinical thrombosis. Current observational data suggests rates of 12 to 40%, based on computed tomography findings. There is a clinical need for a more sensitive non-invasive method of detecting valve thrombosis.

Inclusion Criteria:

• ability to give informed consent
• >1 month post-surgical or transcatheter aortic valve replacement

Exclusion Criteria:

• Inability to give informed consent
• Pregnancy or breastfeeding
• Contraindications to iodinated contrast
• Contraindications to anticoagulation
• Use of anticoagulants during the post-operative period prior to screening
• Extreme claustrophobia
• Chronic kidney disease (with estimated glomerular filtration rate <30 mL/min/1.73m2)
• Metastatic malignancy
• Inability to tolerate the supine position

Patients >1 month post-bioprosthetic aortic valve replacement.