<prompt> String sign in angiography is suggestive of:Aerial dissectionAoa aneurysmStrokeNone of the above  <response>: Traditional angiography remains the basis of diagnosis and characterization of aerial dissection. Angiographic abnormalities include stenosis of the true lumen, or string-sign, visible intimal flaps, and the appearance of contrast in the false lumen. Four-vessel cerebral angiography should be performed when suspicion of dissection exists. Ref: Schwazs principle of surgery 9th edition, chapter 42. 