Impact of plaque haemorrhage and its age on structural stresses in atherosclerotic plaques of patients with carotid artery disease: an MR imaging-based finite element simulation study.

Plaque haemorrhage (PH) in atherosclerotic plaques is associated with recurrent thromboembolic ischaemic events. The healing process predominantly involves the repair of the plaque rupture site and the replacement of fresh PH with chronic PH, which is either reabsorbed or replaced by fibrous tissue. The extent to which the presence of PH, and its type i.e. fresh or chronic, affects plaque stability remains unexplored. Finite element analysis (FEA)-based biomechanical stress simulations can provide quantification of the percentage contribution of PH and its types to the biomechanical stresses of plaques, thereby providing information about its role in plaque stability. Fifty-two patients with atherosclerotic carotid disease underwent high resolution magnetic resonance (MR) imaging of their carotid arteries in a 1.5 Tesla MR system. Twenty-three patients had MR-identifiable PH and were selected. Only those images of these patients were used for simulations, which had evidence of PH. Manual segmentation of plaque components, such as lipid pool, fibrous tissue, calcium and PH, was done using carotid MR images. Plaque components and vessel wall were modelled as isotropic, incompressible hyperelastic materials with non-linear properties undergoing deformation under patient-specific blood pressure loading. Two dimensional structure-only FEA was used for quantification of maximum critical stress (M-CStress) of plaques. The median M-CStress of symptomatic patients with fresh PH was 159 kPa (IQR: 114-253). Because PH usually occurs within the lipid pool, when the simulation was repeated with lipid pool replacing fresh PH to simulate the pre-rupture plaque state, M-CStress was reduced by 26% [118 kPa (IQR: 79-189) (P=0.001)]. When fresh PH was replaced with chronic PH it resulted in a 30% reduction in the M-CStress [118 kP (IQR: 79-189), (P=0.001)]. PH affects stresses within atheroma to various degrees depending on its type, thereby influencing plaque stability to a different extent, with fresh PH significantly increasing the biomechanical stresses. Plaque component-dependent stress analysis has the potential of identifying the critical nature of various plaque components.