Winners of the EFSUMB Young Investigator Award 2016

Patient-Specific Mechanical Characterization Of Abdominal Aortic Aneurysms Using 4 D Ultrasound

E.M.J. van Disseldorp^1,2, N.J. Petterson¹, M.C.M. Rutten¹, F.N. van de Vosse¹, M.R.H.M. van Sambeek², R.G.P. Lopata¹

1. Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands

2. Department of Vascular Surgery, Catharina Hospital Eindhoven, Eindhoven, the Netherlands

ABSTRACT

Introduction

Abdominal aortic aneurysms (AAA) are silent killers and the 13^th cause of death in Western society. In this study, methods for wall stress analysis (WSA) and elastography (EL) were developed using 4 D ultrasound (US) to determine patient-specific wall stresses and material properties. These techniques were introduced in the clinic and tested in a subgroup of patients in an ongoing study with 300 patients in follow-up. 

Methods 

In forty patients (AAA diameter 27 – 52 mm), 4D-US data were measured using a Philips iU22 (X6 – 1 transducer). The brachial blood pressure was measured using an arm cuff. The US data were manually segmented. The patient-specific geometry was tracked over time to estimate its displacement field using 3 D speckle tracking. Subsequently the diastolic geometry was converted into a finite element model. WSA was performed assuming a neo-Hookean material model. The model was optimized by iteratively adapting the material properties until the model output matched the 3 D displacements. For seven patients, computed tomography (CT) data were available and used to compare the US-based geometries and wall stresses.

Results 

The 4D-US based 99^th percentile wall stress ranged between 198 to 390 kPa, and the patient-specific material property (G_inc) had a median of 1.1 MPa (IQR: 0.7 – 1.4 MPa). Geometry based on US data showed good similarity indices (0.90 – 0.96) with CT, and the 25^th to 95^th percentile wall stresses were in good agreement. Small aneurysms revealed stresses similar to those in large AAAs. Furthermore, the arterial stiffness increased with respect to AAA diameter.

Conclusion 

This study shows that 4 D US-based WSA and EL of AAAs is feasible and has the potential to aid in AAA rupture risk assessment by identifying patients at risk, and to monitor patients over time by detecting changes in wall stress and material properties. Ongoing work includes a novel automatic segmentation and registration algorithm and long-term follow-up.

Emiel M.J. van Disseldorp received his M.Sc. degree in Medical Engineering from the Eindhoven University of Technology (Eindhoven, the Netherlands) in 2014. During his Masters, he was an Intern at the University of Canterbury, Christchurch, New Zealand where he worked on a mathematical model for neurovascular coupling, which resulted in one co-authored publication. During his master thesis he worked on novel ultrasound methods to perform elastographic measurements in aneurysms in the thoracic ascending aorta in collaboration with the University Hospital of Brussels, Belgium.

He soon afterwards started his PhD, entitled “Quantitative monitoring of abdominal aortic aneurysms using 3 D ultrasound” at the PULS/e group of the Eindhoven University of Technology, and the department of Vascular Surgery of the Catharina Hospital Eindhoven. In this project, a method was developed to perform wall stress analysis and mechanical characterization of abdominal aortic aneurysms using 4 D ultrasound data, which is currently validated in a large group of patients. In his relatively short career, Emiel has (co-)authored five publications and has won the young investigator award at the annual conferences of both the European Society of Biomechanics and the EFSUMB, both in 2016.