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