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': 'Investigation of choice for screening of proximal internal carotid aery stenosis is : \nSelect and explain. \nA. Doppler flow USG, B. CT substraction angiography, C. MRI, D. Angiography (DSA)', 'role': 'user'}, {'content': "Answer: A \nExplanation: Answer is A (Doppler flow USG): 'Stenosis at the origin of the internal carotid Aery can be identified and quantified reliably by ultrasonography that combines B mode ultrasound image with a Doppler ultrasound assessment of flow velocity.'", 'role': 'assistant'}]