Evaluation of carotid artery stenosis

Patient: Had some usual symptoms (curtains for ex.)and doppler ultrasound showed 50% carotid stenosis on left side (I actually could see the narrowed area) Five additional dopplers from the same center (being followed) confirms a blockage. Had a dye angiography performed at a different center and they say my carotids look norml (the x-ray picture did appear normal) Is there an explanation for the different results? I’m assuming the angiography is the most reliable but what could the doppler be picking up if that is the case? And lastly would you suggest that I do at this point to insure normal carotids??

Doctor: Magnetic resonance angiography (MRA) or computed tomography angiography (CTA) are the gold standard procedures to assess for narrowing of the carotid arteries. These investigations can also be used with contrast for higher quality images. MRA, CTA and carotid Doppler are usually undertaken initially to evaluate carotid artery stenosis (narrowing) because they are non-invasive and traditional angiography has a small but significant risk of stroke with the procedure. Conventional angiography is rarely performed; indications include patients who cannot tolerate an MRA or if dissection or  vasculitis (inflammation of the blood vessels) is suspected. Carotid Doppler is operator dependant and the accuracy relies heavily upon the experience and expertise of the ultrasonographer. It can often overestimate the degree of narrowing (stenosis). Carotid artery stenosis may occur with increased age in addition to other cardiovascular disease. To reduce the risk of developing stenosis it is important to control risk factors including high blood pressure, diabetes, smoking and high cholesterol.