Computational simulations of MR elastography in idealised abdominal aortic aneurysms

Abstract

Introduction Patient specific modelling (PSM) of abdominal aortic aneurysm (AAA) aims to predict rupture risk by calculating the peak stress acting on the AAA wall using finite element analysis (FEA). It is hypothesised that magnetic resonance elastography (MRE), a non-invasive technique measuring material properties, can improve PSM by allowing integration of patient specific properties into the model. MRE measurements are, however, dependent on the geometry under investigation as well as the material properties. This preliminary study used FEA to investigate the ability of MRE to achieve reproducible measurements of the elastic properties of the thrombus in different sized idealised AAA geometries.Methods Idealised AAA geometries of diameter 50, 60 and 70 mm were created with material properties based on literature values prescribed. FEA was run with frequencies of 50, 100, and 120 Hz induced into the model. Synthetic noise was applied to the models and the ability of a 3-D Butterworth bandpass filter to remove it's influence was assessed.Results and Discussion In low prescribed shear moduli greatest accuracy was typically achieved at 50 Hz, contrasting with high prescribed shear moduli, where it was achieved at 120 Hz. Variation in measurements across the three AAAs was lowest at 120 Hz with a mean coefficient of variation across all prescribed shear moduli of 9% in contrast to 11 and 18% at 100 and 50 Hz respectively. Bandpass filtering was able to fully recover material property measurements at noise levels of 1 and 2%, but was unable to do so for high prescribed shear modulus values at levels above this.Conclusions Of the frequencies tested here, 120 Hz achieved the most reproducible measurements across the three AAA sizes, though accuracy of measurements at this frequency was compromised in low prescribed shear moduli.

Patient Specific Biomechanics Are Clinically Significant In Accurate Computer Aided Surgical Image Guidance

“…Physics Simulator Theoretical Convergence Study: Standard AR IG validation approach is to measure simulation registration error with a phantom (tissue proxy) or a theoretical model [21], [22]. Because MRE validation has been reported using theoretical models [23] we choose a theoretical validation. We simulate a cantilever beam under distributed load and check for convergence of our simulation method with an established theoretical model of the system and our mesh free model.…”