18 th International Symposium on Computational Biomechanics in Ulm CBU 2013 A Finite Element Updating method for in vivo identification of elastic properties of the human aortic wall based on full field displacement measurement by 3D ultrasound speckle tracking Andreas Wittek a* , Konstantinos Karatolios b , Rainer Moosdorf b , Sebastian Vogt b , Christopher Blase a , a) Goethe University Frankfurt/M., www.praeventive-biomechanik.eu, Germany b) Philipps University Marburg, www.praeventive-biomechanik.eu, Germany *) wittek@bio.uni-frankfurt.de Introduction Computational analysis of the biomechanics of the vascular system aims at a better under- standing of its physiology and pathophysiology and eventually at diagnostic clinical use. Be- cause of the great inter-individual variances such computational models have to be patient- specific with regard to geometry, material properties and applied loads and boundary condi- tions. Yet most of the approaches presented so far are patient-specific only with regard to ge- ometry and blood pressure [1]. We present an approach to determine individual mechanical properties of the abdominal aorta by applying an inverse Finite Element Updating Method (FEU) to in vivo full field displacement data obtained by time resolved three-dimensional ul- trasound (4D-US) combined with speckle tracking [2]. Materials and Methods A discrete displacement field of up to 36 x 26 nodal points on the aortic wall was acquired with a temporal resolution of 10 - 20 Hz by use of a customized commercial real time 3D- echocardiography system including a speckle tracking algorithm (Toshiba Medical Systems, Tokyo, Japan). Spatially and temporally resolved stretch fields were calculated. Diastolic and systolic blood pressure was measured at the brachial artery. Figure 1 Systolic displacement (left) and stretch (right) fields relative to diastolic geometry. A nested iterative FEU was developed to solve two coupled inverse problems [3]: the deter- mination of the prestrains that are present in the imaged wall geometry due to physiological loading [4] and constitutive parameter identification of a nonlinear orthotropic hyperelastic strain-energy function [5]. The deviation of systolic deformation that was measured and cal- culated by FEM using guessed constitutive parameters, respectively, was quantified by an