Stephen Bird

Hi Diane,

For my ICA / CCA ratio I use the PSV in the middle of the CCA.
If you use a proximal PSV it may be influenced by altered haemodynamics generated by the vessel origin. If you use a distal CCA it may be influenced by the beginning of bulb widening.

The CCA mid section I think is the most stable and reproducible reference point.

The debate of should I use 60 degrees always OR should you use the minimum angle possible is as old as I am!

My personal view on this is I like to make everything as optimised as possible at every junction in my scanning.
Hence with steering I use the smallest amount of steering that I require after heel – toeing the transducer as the more steering you use the longer the transmission tissue path and hence the signal to noise ratio will be compromised. So no steering is best (but rarely achievable). Use no steering as your first option but in reality you will need to steer a bit, just steer the minimum amount to give you the desired result.

As for the zero to 60 degrees angle correction debate, I personally go for the lowest angle possible as in theory the lower the angle the more accurate the Doppler equation is at calculating the velocity. So I am happy to use right down to zero, but never go over 60 degrees.

When I steer the box I steer in whatever direction allows me to generate the lowest angle of incidence with the blood flow direction.

So in carotid ultrasound that mostly means you are steering towards the patients head (distally), however there are exceptions when I would steer the other way (towards the patients feet). They would include the proximal CCA, proximal vertebral and sometimes the ICA origin depending on the angle of the bifurcation. The point of steering is to get a lower angle to the vessel, again with zero being best and 90 degrees being hopeless (as you will have a zero Doppler shift). I think in the vertebral image you attached the vessel is curving and you could have steered either way successfully ( I am happy with the image that I have steered correctly).

Yes, with %diameter reduction less than 50% it is important to be more accurate than 16-49% as that range is so broad and the clinical implications are so profound, especially in a younger patient. The diagrams you have attached are correct and that method will generate a reasonable result, however there are some pitfalls. Not many plaques are symmetrical, plaques often contain calcium and shadowing, colour Doppler blooming or bleeding can overestimate the patent lumen etc.
So we have some issues! By all means put a calliper on as you suggest but remember that there are these limitations. Personally I think you can make an estimation by eyeballing the vessel and I am happy to say 10% 20% 30% 40% based on the way it looks. Run a calliper over it and see how close you are.

A proximal CCA interrogation is important as you may detect turbulence or an increased PSV from an origin stenosis. If your first look is in the middle of the CCA you will miss origin pathology.

I don’t do a subclavian PSV measurement as part of a carotid series.
I do them for thoracic outlet syndrome assessment and in this case I do it proximally, adjacent to the head of the clavicle. If I want a representative subclavian PSV I would use the same theory as I described for the CCA, That is pick a spot in the middle of the vessel.


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