The purpose of this study is to determine if the Valiant stent graft is safe and effective in treating patients who have a blunt thoracic aortic injury (BTAI). BTAI is when the aorta has been injured due to traumatic force to the chest area. It is commonly caused by motor vehicle accidents. In most cases it is life threatening and the standard treatment is surgery. Many times when a person has a BTAI they also have other injuries that can affect the results of the surgery.