Magnetic Resonance Imaging for Aortic Function Evaluation in Thoracic Aortic Aneurysms

Thoracic aortic aneurysm is a common cardiovascular disease consisting of marked dilation of the aorta. Aortic aneurysms carry a high risk of life-threatening complications such as aortic dissection or rupture. Classically, maximum aortic diameter has been used as the sole descriptor of aneurysm severity and is considered the main predictor of complications. However, maximum aortic diameter measurement is often poorly reproducible and about 60% of type A and 80% of type B aortic dissections occurred in patients with an aortic diameter inferior to that recommended for the indication of elective surgical treatment. Therefore, new biomarkers for risk stratification in thoracic aortic aneurysm are needed. Cardiovascular magnetic resonance (CMR) imaging is a non-invasive imaging technique widely used for diagnosis, clinical follow-up and research in thoracic aortic aneurysms. CMR applications to thoracic aortic aneurysms are generally based on either cine CMR images, which are time-resolved images providing dynamic structural visualization, or phase-contrast images, which utilise a flow-encoding gradient to assess time-resolved velocity data. Particularly with 3D velocity encoding (4D flow MRI), phase-contrast imaging permits detailed study of haemodynamic in thoracic aortic aneurysms while cine CMR is often used to assess aortic geometry and its changes through the cardiac cycle or during follow-up. The possibilities offered by CMR for studying thoracic aortic aneurysms and a description of their applications in Bicuspid Aortic Valve (BAV) and Marfan patients are here reviewed.