drgregory said:
if you dont mind me picking your brains, what is the clinical effectiveness of this procedure...
a friend of mine whom i work very closely with often sends for these, however an internal med physician who i work with claims it is utterly worthless. from my perspective (as an eye doctor), i'll often times have the following scenario:
diabetic, hypertensive patient with markedly asymmetric diabetic retinopathy. i call primary care physician and say "please check for carotid artery disease per findings noted on retinal examination blah blah blah". how many PCPs are sending them on for duplex vs just MRA?
Despite the fact that there is good correlation between non-invasive studies (e.g., Carotid US, MRA, CTA) with the gold standard (i.e., carotid catheter angiography), they are not perfect. The question often comes down to whether the patient is symptomatic and what is the percentage of carotid narrowing and residul lumen size. Carotid US tries to estimate the degree of narrowing by using various flow and velocity indices. MRA visualizes flow directly but can over- or under-estimate the degree of narrowing (usually overestimate), but things have become much more accurate these days. CTA is quite accurate except where you have dense plaque which makes accurate determination of residual lumen difficult. So all have their own limitations. US is very operator dependent, and the reference ranges varies between the different labs, even in the same hospital. Just a few months ago when the cardiologists started doing carotid stents, they decreased their reference range for calling something severe on US by 20cm/s so they could funnel more people for treatment. In our hospital, there are four US labs, in radiology, neurology, vascular surgery, and cardiology. The first two have similar criteria, cardiology has very low thresholds for calling something severely narrowed, and vascular surgery is in between.
Bottom line, see what the US lab you send to does, and if their results are in anyway tied to self-referring patients for treatment. Avoid ones who want to stent or CEA anyone coming through the door. US is a good screening tool for lower neck and bifurcation disease, but only of moderate utility in diagnosing disease in the origin of the vessels from the aortic arch and more distally in the neck or skull base, since it can't directly visualize those areas.
Given the above problems with US use, I have seen more and more people refer patients directly for MRA or CTA. The advantage of MRA and CTA is that you get the whole system from aortic arch to the intracranial vessels.
I am not advocating any one the other for general use, but specific patients made need one or the other, or may even need two of the three to come to an accurate diagnosis.
