This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': 'The most important sign of significance of renal artery stenosis on an angiogram is – \nSelect and explain. \nA. A percentage diameter stenosis > 70%, B. Presence of collaterals, C. A systolic pressure gradient > 20 mm Hg across the lesion, D. Post–stenotic dilatation of the renal artery', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The presence of arterial collaterals indicates that renal artery stenosis is hemodynamically significant. The diameter of stenotic segment may also give an indication of hemodynamic significance, but is only reliable if the stenosis is either very severe or minimal .', 'role': 'assistant'}]