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Dear Steve,
1) When obtaining traces, do you try to reduce the Doppler angle to make it <60 and closer to 0? Or do you try to keep it as close to 60 deg when taking all traces from CCA-ICA to make it consistent?
I find that velocities can be variable when multiple sonos perform a scan on a single patient over a short period of time and I understand that plaque doesn’t resolve by itself. One time my senior and I try to get 280cm/s (previous scan) for a prox ICA but we can only get 220cm/s.
2) Do you take off color box when using pulse wave to obtain a reading?
3) Do you set the color scale between 30-40 cm/s or do you keep it as is for consistency between scans? I read this article: Sonographic Examination of the Carotid Arteries (2005) by Hamid and they recommend to set this range of velocity at the color bar at the top left of the screen.
Again I just want to stress on the consistency issue with velocities obtained here.
4) What do you do when you see a tortuous ICA? Do you just obtain a reading at prox and dist ICA excluding the tortuous part and hope theres no stenosis there? I can only check the tortuous part by B-mode and filling of the vessel to make sure there’s no narrowing but I don’t take traces there.
Best regards,
Linh -
Hi Linh,
Good questions.
The first question is an age old debate and people have different views as to stay at 60 degrees or alternatively anything less than 60 is good. Personally I use the lowest angle correction I can as this gives the least mathematical error for every degree of angle correction error you are using. So I am happy to use really low angle correction angles if the topography of the neck allows but I never go above 60 degrees. There’s one more point I would make here and that is the amount of BEAM STEERING that you are using as modern machines allow a lot of beam steering and if you use excessive amounts the signal to noise ratio deteriorates. So my perfect solution now that we have two competing decisions to make is to use only a low to moderate amount of beam steering and keep my angle correction as low as I can never exceeding 60 degrees. Win – Win I think!
Yes, I see the same thing in my clinical practice where I can not achieve the same high velocity as a previous scan. With modern Statins plaque can resolve slightly over time so this is not impossible, however usually when I review the previous examination I see that there is some technical error like inaccurate angle correction or failure to place the sample gate in the jet stream of the stenosis etc and this accounts for the error. We all try our best but perfection is rare.
Point 2: I do not take the colour box off as I use it until the last second to perfectly place my sample gate and set my angle correction. But then I use the update button so the colour function freezes when it takes the pulse wave data. That way I do not compromise the pulse wave quality. In other words I do not like using a Triplex function. Triplex is rubbish my view as all 3 functions are severely degraded. I would only use it in rare circumstances such as chasing a pulse wave waveform on a paediatric case where the child is non compliant and moving or the same situation with a non compliant adult. If the situation is fairly controlled (like it is most of the time) I see no place for triplex imaging.
Point 3: I do not agree this is good at all. I change my colour scale all the time as remember colour displays average Doppler shift data and is not angle corrected so as a vessel changes direction relative to the beam or if we steer more or less we need a different scale to match the new environment. For me it is simple, I reduce my colour scale until I get a tiny bit of aliasing during peak systole and scan at that level. The toy touch of aliasing alerts me to the area of maximum Doppler shift (not necessarily highest velocity) and if more aliasing occurs I increase my scale slightly, if it disappears I reduce it slightly. It gives me a really fast and eye catching way to help me to place my angle corrected pulse Doppler sample volume which is what provides me with the REAL data I am after. At the end of the day colour Doppler is simply a navigation tool, overview assessment tool and a sample volume placement aid. Pulse wave is the real data provider.
Point 4: Tortuosity provides challenges. Firstly see if the colour Doppler fills the lumen nicely and you may need to steer more or less and even in the reverse direction to assess the whole vessel. This will give you an idea of the presence or absence of a harm-dynamically significant stenosis. Then as before get busy with the pulse Doppler. The tortuosity does not bother me. Place a small sample gate in the lumen where the colour Doppler set as I described prior shows the highest velocity. If you are working on a bend in a vessel the colour Aliasing you are looking for will not be in the centre of the lumen but on the outside of the bend slightly and this is where I place the sample gate. Angle correct as best you can and this may be tricky. If you magnify the B-mode and colour image significantly this will help considerably. I don’t think it is good enough to sample before and after the tortuous part, I would always try and sample at least once within it as well and work hard on my sample volume placement and angle correction accuracy.
In tortuous vessels it is common for me to use a “reverse steering” technique where I steer the beam proximally as opposed to the distal steering we generally use in the ICA.
Steve
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Dear Steve,
Thank you so much for your detailed response. Carotid is really challenging when it is not a straightforward NAD scan.
1) I do think that beam steering is overused, especially with machines like the Philips Affiniti 70 where people rave about how wide of a range the beam steering has. What I have always learnt from angle correcting Portal vein, MCA, UA, etc. is that you always try to get Doppler angle to 0 deg, not as close to 60 deg, so I am very confused when people say to keep it 60 deg for Carotid.
Also, I did not know there are ways to reduce plaque size like Statins.2) I have not used Triplex but now I know why not to use them. Do you use I-scan (or Q-scan?) (on Canon machines) to let the machine optimise your Pulse wave reading? I often have to adjust the scale manually to have a nice spectral trace graph.
3) More questions on colour: apart from colour scale, do you ever adjust colour frequency to increase sensitivity to light up the vessel? Or do you use Power Doppler to delineate the subtle hypoechoic plaques?
4) If I ‘walk the vessel’ as I obtain the trace in tortuous part of the vessel, then by what you say, I should stop and change the beam steering after the bend then.
5) I did another scan where the patient is young and heathy, but her CCA prox and dist on both sides are high (150 at prox to 130 cm/s at dist). There is no obvious plaques at all. I obviously can’t call there is a 50% stenosis in CCA but how do you explain the high velocities in the CCA?
6) Sometimes I cannot identify the vertebral art between the transverse processes at mid neck. But as I use Colour and sweep laterally and medially, I can see a vessel diving down and the waveform is like vert art. Is this a normal variation that vert art is outside the vertebrae?
Best regards,
Linh -
Hi Linh,
I agree, they can be really easy and beautiful or really difficult!
I will answer your questions.1: Yes, I think beam steering is overused and more beam steering should only be used when I can not heel and toe the transducer to keep my angle below 60 degrees.
In the carotid system anything less than 60 degrees is OK but I think if you are using more beam steering to get a lower angle you are creating a linger tissue path for the beam and the signal to noise ratio and the sensitivity will suffer. So a balanced approach using minimal beam steering, heel and toe technique and keeping your angle less than 60 degrees is the correct approach. Like many things in life a balanced approach is best.
Yes there is some evidence the modern stations with other lifestyle changes etc can reduce plaque slightly over time.2: Personally I don’t use these functions as I like to adjust things myself, however they do work fairly well on the current machines and it is a nice short cut if you want to use it.
3: Colour frequency and also frequency in pulse wave are really great things to adjust. I commonly adjust them for all Doppler work and it makes a huge difference. Same principles apply as your b-mode image, if it is superficial (CCA on a skinny neck) use a higher frequency then drop it down for the vertebral as it is deeper.
I don’t use Power Doppler much at all to be honest. you can use it to delineates oft plaque but be careful with Power Doppler as it blooms and overwrites the plaque easily. I think there are better options to Power Doppler. Try SMI, ADF, B-Flow etc.4: Yes the beam steering should be adjusted and optimised as you work your way through a tortuous vessel.
5: Yes, young patients can have this hyper dynamic circulation and if you use the 2:1 PSV ratio as a guide you will see there is no stenosis.
6: Yes this is normal. The vertebral artery can stay outside the expected location between the transverse processes and then dive down. You see this fairly commonly . Also the vertebral artery is a great example of where less beam steering is really important and a low Doppler frequency in both colour and pulse wave is a great trick, especially on a thick bull neck.
Steve
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Dear Steve,
So for point 3) & 6), we reduce colour frequency to detect low flow from the vert art? (better sensitivity?)
Then once identify, put the pulse wave on. Reducing pulse wave frequency will have the same effect as reducing the scale/PRF? so as to utilize the spectral trace real estate to magnify the waveform shape?
I don’t know if my understanding of colour and pulse frequency adjustment is right as I have never adjusted these. So far, I only adjust gain and scale.
Linh
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No not really,
Scale / PRF are the same thing and this should be set low to see slow flowing blood and higher for faster flowing blood.
The transducer frequency is a completely different thing and you should think about it the same way you do when doing b-mode ultrasound.
Colour Doppler and Pulse wave Doppler frequencies can be adjusted on some machines and I would use the higher frequency option if I am scanning more superficial (slim patient / superficial vessel) and lower for deeper vessels (large patient / deeper vessel) . So for a carotid study the vertebral artery is always a bit deeper and if you can lower your colour and pulse wave frequency this may help. For the vertebral I would also typically lower the scale / PRF a bit as the velocities are generally lower than the ICA etc.Steve
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Absolutely it does,
It is just as important,
In pulse wave you should use the most appropriate Doppler frequency,
If you are using a higher frequency and getting better results with colour Doppler use the same trick with pulse wave and similarly if you are lowering your colour Doppler frequency to get the best result mirror this with the pulse wave.
Ultrasound is simple sometimes and the old basic principles of selecting the correct frequency hold true. In the past (early in my career) frequency was about the only parameter we could change and we lived and died by our frequency decisions. Now we can alter so many parameters we have forgotten the most basic and powerful of them all; Frequency.
Steve.
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Indeed, there’re many parameters to keep in mind: frequency in B-mode, Colour, Pulsed, gain, scale, beam steering, Dopple sample gate, angle, heel and toe, etc. It is quite overwhelming!
For grading stenosis, does your PSV has to agree with the ICA/CCA ratio when trying to categorise the extent of a stenosis? For example for a 70% stenosis, if I get >270 cm/s for PSV, do I need to get a ICA/CCA of >4 to make it consistent or vice versa?
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When you enjoy the vascular principles and haemodynamics webinar on the website it outlines all of these adjustments you can make when performing Doppler ultrasound.
Your question about PSV and ICA/CCA ratio is a good one and it can be answered with one small word ” or ”
It is only 2 letters but it gives you the answer.
I have attached a screenshot from the ASUM website standards of practice for carotid ultrasound.
This is the standard grading chart recommended in Australia.
If you have never checked ASUM out I highly recommend it
asum.com.au
There is a lot of great material available.
I have the privilege of being an honorary and have had a long association with ASUM.
The word “or” in the grading chart indicates that if either the PSV or the ICA/CCA ratio criteria are met you are in that category and both are not required.
Please see attached.
Steve
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