Assessment of aortic blood flow patterns using 4D-flow MRI
Can blood flow patterns from 4D-flow MRI be used to predict aortic wall degradation?
Imperial College London
Duration of Study in the UK
3 years, 0 months, 1 days
Summary of Research
Enlargement of the ‘ascending aorta’, which is made up of the valve and large artery exiting the heart, is becoming increasingly common, partly due to an ageing population. This can require major surgery, either planned or emergency, to replace the ascending aorta. One of the difficulties in patients with aortic root ‘aneurysms’ (where the aortic root is enlarged and at risk of bursting or tearing) is that they often feel no symptoms, making diagnosis very difficult.
This state-of-the-art research study aims to help assess whether a modern imaging test (called 4D flow MRI), can be used to predict if patients have a weak ascending aorta. We hope to do this by performing 4D-flow MRI scans on a group of 60 patients (Group 1) who are due to undergo surgery to replace their ascending aorta. At the time of the operation, their removed aortic tissue will be tested for its strength (with a test called biaxial mechanical testing) and composition (with a test called metabolomics, which looks at small lipids). Only tissue that is not required for medical tests and is due to be discarded will be obtained. By correlating these tests, we will be able to assess whether findings from the scan can predict aortic tissue at risk of bursting or tearing. We will also recruit 10 healthy volunteers (Group 2), who will act as a comparison group.
Summary of Results
adopted a multimodal approach to characterising TAA in a cohort of patients focusing on four key areas of research: i) computational pathology; ii) targeted genetic sequencing; iii) mechanical characterisation of TAA tissue; and iv) aortic flow dynamics. Through this work, we have demonstrated three key findings. Firstly, medial degeneration occurs in hotspots of disease, affecting the outer curve more so, and microstructural features are directly related to in-vivo measures of mean arterial pressure and pulse wave velocity, as well as a potential link to underlying genomic variances. Secondly, the TAA wall is stiffer in the circumferential direction with a lower peeling force compared to longitudinally orientated aortic wall. Thirdly, wall shear stress (WSS) as deciphered from dynamic imaging, was higher on the outer curve of the aorta, and strongly associated with areas of reduced aortic tissue peeling force and aortic wall degeneration. Most importantly, TAA material properties were unrelated to aneurysm diameter.
These findings support the hypothesis of flow mediated degeneration in TAA pathology and set the stage for more translational work to further link aortic flow measurements with disease severity.
HSC REC B
Date of REC Opinion
15 Aug 2017