<prompt> Investigation of choice for screening of proximal internal carotid aery stenosis is :Doppler flow USGCT substraction angiographyMRIAngiography DSA  <response>: 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. 