Diagnosis of Thoracic Aortic Aneurysms Incidental x-ray finding Confirmation by CT angiography (CTA), magnetic resonance angiography (MRA), or transesophageal echocardiography (TEE) Thoracic aortic aneurysms are usually first suspected when a chest x-ray incidentally shows a widened mediastinum or enlargement of the aortic knob.