When internal carotid siphon are investigated via orbital window its velocity has something to do with position of fistulae orifice, which can be estimated roughly by i he extent of blood steal phenomenon.

• 经眶窗检测颈内动脉虹吸段时；其流速受瘘口所在位置的影响；观察颅内盗血情况可粗略估计瘘口大小.