Three-dimensional ultrasound in themanagement of abdominal aorticaneurysm

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Abstract

Objectives: Clinical implementation of 3D ultrasound (3D-US) in vascular surgery isin its infancy. The aim of this thesis was to develop novel clinical applications for 3DUSin the diagnosis and management abdominal aortic aneurysm (AAA).Methods: Four principle clinical applications were investigated. 1) Intraoperativeimaging – The ability of 3D-US to detect and classify endoleaks was compared withdigital subtraction angiography in patients undergoing EVAR. 2) Detection andclassification of endoleaks following endovascular aneurysm repair (EVAR) – The abilityof 3D-US to accurately detect and classify endoleaks following EVAR was compared toCTA and the final multi-disciplinary team decision. 3) AAA volume measurement –measurements using magnetic and optically-tracked 3D-US were compared to CTA. 4)Biomechanical analysis – the challenges of using 3D-US to generate surface models forbiomechanical simulation was explored by development of an interactivesegmentation technique and comparison of paired CT and 3D-US datasets. Optimalresults were used in finite element analysis (FEA) and computational fluid dynamic(CFD) simulations.Results: 3D-US out-performed uniplanar angiography for the detection of endoleaksduring EVAR. This approach allowed contrast-free EVAR to be performed in patientswith poor renal function. 3D contrast-enhanced ultrasound was superior to CTA forendoleak detection and classification when compared with the final decision of themulti-disciplinary team. Optimal results for AAA volume measurements were gainedusing an optically tracked 3D-US system in EVAR surveillance. However, thereremained a significant mean difference of 13.6ml between CT and 3D-US. Completetechnical success of generating geometries for use in biomechanical analysis using 3DUSwas only 5%. When the optimal results were used, a comparable CFD analysisunder the conditions of steady, laminar and Newtonian flow was achieved. Using basicmodelling assumptions in FEA, peak von Mises and principle wall stress was found tobe at the same anatomical location on both the CT and 3D-US models but the 3D-USmodel overestimated the wall stress values by 41% and 51% respectively.Conclusions: 3D-US could be clinically implemented for intra-operative imaging andEVAR surveillance in specific cases. 3D-US volume measurement is feasible but futurework should aim to improve accuracy and inter-observer reliability. Although theresults of biomechanical analysis using the optimal results was encouraging andprovided a proof-of-principal, there are a number of technical developments requiredto make this approach feasible in a larger number of patients.

Keyword(s)

abdominal aortic aneurysm; aneuryms volume; biomechanical analysis; endoleak; endovascular aneurysm repair; three-dimensional ultrasound

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