A method of repairing an article includes removing an undesirable section of the article, attaching a repair section to the article at a location from which the undesirable section has been removed, and mechanically working the repair section to achieve a reduction in a cross-sectional area of the repair section. The sub-reflector has a sub-reflection surface in a form of a paraboloid of revolution. This can indicate the propensity of the patient to experience episodes of vein thrombosis or arterial thrombosis.