The purpose of the study is to describe Sodium Fluoride uptake (using Positron Emission Tomography-Computed Tomography - PET-CT) following Endovascular Aneurysm Repair (EVAR) and to determine whether Sodium Fluoride PET-CT can predict the development of endoleaks.

Abdominal aortic aneurysms are a leading cause of death in the United Kingdom. Surveillance programmes and pre-emptive surgical repair are lifesaving. Traditional open surgical repair is associated with major perioperative morbidity and mortality and there has been a move towards minimally invasive Endovascular Aneurysm Repair (EVAR), which reduces these early risks. However, the cost effectiveness and long-term clinical effectiveness of EVAR is undermined by concerns of durability due to the development of endoleaks and late aneurysm rupture secondary to progression of native aortic aneurysm disease and stent graft failure. It has previously been demonstrated that 18F-Sodium Fluoride Positron Emission Tomography can predict progression of aneurysm disease and is associated with greater rates of abdominal aortic aneurysm expansion and the future risk of rupture or surgical repair.

The investigators here wish to examine whether 18F-Sodium Fluoride on Positron Emission Tomography uptake (i) is increased in patients with endoleaks or related complications, (ii) can prospectively predict the likelihood of developing endoleaks in patients undergoing EVAR, and (ii) is a feasible approach to select patients for EVAR with a reduced future risk of stent graft failure and re-intervention. The investigators believe that there is a compelling scientific rationale for this approach with major translational potential to better select subgroups of patients for EVAR and ultimately improve their outcome.

Inclusion Criteria:

• A diagnosis of AAA as defined by the European Society of Vascular Surgery guidelines on the management of aorto-iliac artery aneurysms, and having undergone endovascular repair within the recommended Instructions For Use (IFU) by the manufacturer. ['Endoleak' and 'No Endoleak groups only]
• Complication will be defined as any type of endoleak or stent graft migration ['Endoleak' group only].
• A diagnosis of AAA requiring endovascular repair OR a diagnosis of juxtarenal AAA requiring fenestrated endovascular aneurysm repair as defined by the European Society of Vascular surgery guidelines on the management of aorto-iliac artery aneurysms and planned EVAR or fenestrated EVAR surgery. ['pre-EVAR' group only]
• Minimum age: 50 years. No maximum age.
• Retain capacity for informed consent

Exclusion Criteria:

• The inability of patients to undergo PET/CT scanning
• Chronic kidney disease (eGFR ≤ 30 mL/min/1.73 m2)
• Major or untreated cancer
• Pregnancy
• Allergy or contra-indication to iodinated contrast
• Inability or unwillingness to give informed consent
• Life-expectancy of less than two years
• Known history of connective tissue disease

The study population will consist of individuals with an abdominal aortic aneurysm (AAA). The first part of the study (Study 1 - Case Control Study) will recruit patients with existing EVAR in to two groups: patients that have an endoleak or related complication (endoleak group, n = 22) and those that have remained complication-free (no endoleak group, n = 22). We will also prospectively recruit patients who are yet to receive EVAR or fenestrated EVAR (pre-EVAR group, n = 100) for the (Study 2 - Cohort Study).

There will be four patient identification centres from which patients will be recruited: NHS Lothian, NHS Lanarkshire, NHS Greater Glasgow and Clyde, and NHS Tayside.

There are no plans for individual participant data sharing.