Thermodynamics and structural stability of tissues for bio-imaging analysis – The case of intracranial aneurysm rupture risk assessment

Abstract Based on thermodynamic principles, structure stability analysis like stress response and fracture formation is well established for inorganic but not for organic bio-materials. In this study, three equations were established to assess intracranial aneurysm (IA) rupture risk based on patient's IA and internal carotid artery (ICA) angiography images, by incorporating tissue thermodynamics. Our objectives are: (1) establish foundations to help understand the physics behind the observed morphological changes prior to IA rupture, and (2) provide first-principles equations to aide in rupture risk assessment. Subsequently, we validated the new equations using available experimental and numerical simulation results, and revealed new IA rupture physics. In particular, our models correlated well with most of the available experiment and computer fluid dynamics simulation data. Among the three common structure failure modes, the axial stress and the bending moment loading are the control mechanism. The rupture risk reaches its peak when (1) the aneurysm inclination angle (ω) is close to 63.4°, (2) IA diameter ICA diameter ≈ 1.6 , and (3) IA length IA diameter ≫ 1 . This study provides strong physical foundations and sound understanding to aid in rupture risk assessment. It presents insights on detailed thermodynamics that govern the previously observed IA rupture behaviors, reported from both experiments and numerical simulations. By integrating angiography images with first-principles tissue thermodynamics, we (1) advance the IA research, which is currently dominated by experimental and imaging-data-statistic approaches, and (2) introduce Calphad research into a new exciting research field - bio-imaging analysis.