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
An asymptomatic old patient presents with bruit in the carotid artery. Which of the following is the investigation of choice? 
Select and explain. 
A. Doppler ultrasonography, B. Internal carotid angiography, C. Aortic arch angiography, D. Spiral CT angiography
A: Doppler ultrasonography
Answer: A: Doppler ultrasonography 
Explanation: Bruit over carotid artery suggests carotid artery stenosis.
Duplex scanning (B-mode scan and doppler ultrasonic velocimetry) is the method of choice for assessing the degree of carotid stenosis.