TTA Stent Graft System. Specification: Aortic stent graft system-should enable endovascular treatment of descending thoracic aorta aneurysms. The stent graft should come in various lengths and diameters. It should consist of 1. Self expanding tubular endoprosthesis composed of a polyester graft fabric and a spring scaffold made from nitinol wire. 2. Radiopaque markers are to be sewn to the fabric to radiographically visualize the edge of the graft material to provide a guide to the minimum ove