A method of determining wall stress in an abdominal aortic aneurysm is disclosed. The method includes determining, from anatomical image data, respective first stress values at locations on the wall, based on the aorta having substantially uniform stiffness. The primary direction of stress those locations are determined, and the locations of calcified regions (20) are then determined. The distance to the nearest calcified region is then determined for each location not corresponding to a calcified region, and the additional stress caused by the calcified regions is then determined from values stored in a memory.