Carotid Artery Protocols and Standards

Protocols and Standards in Carotid Imaging

We're gonna talk about protocols
and standards in the carotid.
And I am probably the biggest standard
protocol person that you will ever meet.
It makes it so much easier for the sonographers
and the physicians when all the exams are performed the same
way when the annotation is the same way,
and it makes it a lot easier
because there's a lot less typing.
And we have standard protocols
for almost all of our examinations,
and I think that's very, very important.
We're gonna talk about the protocols
and the first thing you need to do is
to optimize your gray scale imaging,
because if you don't see it on gray scale,
then
because that's always your first line exam,
you always compare what you see on gray scale imaging
to color and spectral doppler.
So you need to choose to correct transducer.
It's a trade off between penetration and image resolution.
And I personally have a transducer that I hate,
and it's used in almost every carotid artery examination.
And that's because one of my colleagues likes it.
And occasionally he wins the battle
because you can get a lot better penetration with
that nine megahertz.
I personally prefer to use a 12 megahertz for a carotid
because I can see gray scale,
I can see plaques so much better.
But the stenographers end up taking the path of least,
least resistance, which is usually to use the nine.
If they look at a patient, say,
that's a big patient,
I'm just gonna use the nine, I'm not gonna have to fool
with the transducer changing.
But then you need to optimize your color
and spectral doppler, and you always need
to angle correct always.
And that goes without saying.
Then never use an angle greater than 60 degrees
because you're not gonna get a
anything
that's meaningful in terms of a PTO velocity.

Gray Scale Imaging Protocol

So in terms of the imaging protocol for the gray scale,
you should do proximal
and distal common carotid artery,
both in the lung and the trans.
And when you take those images, the mid common carotid,
common carotid artery will come for free.
And then you need to evaluate those with color
and spectral doppler in the longitudinal plane.
And by the way, this reminds me there is a
protocol, S-R-U-A-I-U-M
and a CR have gotten together on
carotid artery protocols.
And they are on the websites of those respective
places and of those respective societies.
So you need to look proximal and distal.
And then the distal CCA peaks his dog velocity, measure
that two centimeters from the bifurcation.
Why two centimeters? Why not one? Why not three?
Well, it's standardized
because there have been a few studies that show
that depending on where you measure in the CCA,
you're gonna get a different
PTO velocity number even in the same patient.
So we're all trying to standardize what we do
so we can compare apples and apples.
So you assess the plaque in the carotid bulb by gray scale,
and that's in the long and the trans.
And then we also take a color
and spectral doppler in the longitudinal plane.
And that's a little bit of an odd waveform.
I don't usually pay attention to that, but sometimes I do.
If there's significant stenosis in the bulb
and it doesn't extend too much into the ICA.
So sometimes that will help you most of the time that
that piece, the color
and spectral doppler in the bulb is not all that useful.
But then we look at the bifurcation
and assess the amount of plaque.
Because you're on the gray scale.
You're trying to say, okay, how much plaque is there?
Am I gonna believe what I get in the color
and spectral doppler?
How much extra? How much extra playing
around am I gonna need to do with the spectral
and color doppler given the amount of plaque?
And does it all make sense?

ICA Protocol

So in the ICA
proximal I-C-A-C-C-A in the long
and the trans on the gray scale, and then color
and spectral doppler in the longitudinal plane,
and in the IICA with color
and spectral doppler, we look at the proximal mid
and distal peak systolic velocity
and end diastolic velocity.
And this will be in your, this is in your handouts.
So in that CD gray
scale, same thing.

ECA Protocol

But we only really look at the proximal ECA, both long
and trans in the gray scale.
And then colorant spectral doppler in the
longitudinal plane.
And really, you really only care about P dog velocity.

Vertebral Artery Protocol

Vertebral artery, we really don't
look at that in the gray scale.
Sometimes it's quite challenging to see.
And so we really just look at it in color
and spectral doppler in the longitudinal plane.
And then we always take an image of the table.
All of these ultrasound devices have
tables on them that will calculate the ratios automatically.
But you need to be familiar with
what your particular ultrasound equipment uses
and how it calculates its I-C-A-C-C-A ratio.
Do you all know that, how it calculates it?
I see at least one good one person that's that knows
that this is really very important.
There's a couple of options
and the manufacturers may have decided for you,
but you need to know what the answer is.
So option A,
use the highest peak systolic velocity in the ICA
and by highest peak systolic velocity in the ICA.
They will take it wherever it happens.
If it's in the distal, even though it's maybe from an artery
that's diving down and there's really not a stenosis
or the mid or the proximal, it'll take the highest.
Option B is proximal ICA peaks of salt velocity.
So you need, you need to know which one, and,
and I'll show you an example of that in a minute.

Example of a Normal Study

So this is an example of a beautiful common, I'd like
to have a common that looked like that all of us would.
Here is the distal common.
So these are typical gray scale images.
Here's the ICA, maybe a tiny little bit of plaque,
maybe a tiny bit there.
There's a little bit of plaque in the ECA here,
but we'll be able to figure out
that it's ECA from all the methods
and maneuvers that we talked about in the prior lecture.
And then we look in the transverse plane in the proximal
CCA distal CCA,
the bulb, bifurcation.
And then we start with the color
and spectral doppler you don't need,
you can do both on the same one.
You don't have to do color all the way up
and then spectral all the way up.
So this is a typical normal study for proximal CCA.
Here's the distal
C-C-A-I-C-A and
So you want the takeoff off the ICA
and here is the proximal ICA
always display the angle correction.
So you know, if that angle
that was performed is under 60, here's the mid.
And you can see this is interesting.
I can't see the color box.
See here, you can see the angle
and to see whether it's, if there is a jet, if it's parallel
to that or if it's posterior to the posterior,
if it is angled with the posterior wall,
if there's no stenosis.
But I can't see that on this image
because the box with the calculation goes over it.
So my stenographers are so wonderful, they
take another one without that table.
They show me exactly when a good job they did in terms
of measuring and the angle.
So you need to be able to see the data
that they're giving you.
And then here's the distal ICA
and again an evaluation of the actual angle.
All these need to be angle corrected.
And then this is the ECA
and P systolic velocity measurement in the ECA
and that's a normal standard carotid.
And then here's the vert. Now here's the table.
This is on a Sequoia.
And you can see that the
proximal measurement is 0.41 here,
and mid is
0.41, and then distal is 0.44.
So actually this machine took the 0.44,
which is the distal peak systolic velocity.
So you have to know what your machine is doing
'cause you're responsible for it.
So that's the normal imaging protocol.

Standards for Carotid Stenosis

Now, let's get to the standards. This is pretty interesting.
Back in the day when I was a resident, I already spoke
of the fact that we really didn't have to measure a table.
We just looked at peak onic velocity ratios.
But we've gotten a little bit more sophisticated than that.
And this is again, to remind you that
that peaks dog velocity goes up with diameter stenosis.
And we've talked about this table.
So what degree of stenosis is important?
Well, it has been found
that crowded endarterectomy is more beneficial than medical
therapy in symptomatic patients with 70 to 99% stenosis.
And it's a little bit frustrating
because one study will use 70%, another study will use 60%,
another study will use 80%.
And yet the ultrasound versus angiography studies might have used a different cutoff.
So all of these are pretty challenging to
figure out exactly what you should use.
Well, the asymptomatic carotid atherosclerosis sclerosis
study showed stroke reduction in patients
with greater than 60%.
So again, what's the difference in PTO velocity versus
70 versus 60?
And this is also to remind you that
there are also different ways of measuring the
lumen diameter.
It's basically what's the denominator?
So here the NASA study is looking at the distal
ICA, whereas in the old days, we used
to look at the proximal CCA as some kind of evaluation
And the European crowded surgery trial looked at
the overall bulb.
So again, when you're reading the literature critically,
you have to say, what are their standards?
How are they measuring it?
And look into it very, very carefully.
Well, the Society of Radiologists
and ultrasound had a consensus conference where they had
vascular surgeons, they had cardiologists,
they had radiologists,
and they came up with this table several years ago.
And if it's normal, you,
the PTO velocity is gonna be less than 1 25.
You're not gonna see a visible stenosis.
The I-C-A-C-C-A ratio is gonna be less than two
and end diastolic velocity is gonna be less than 40.
So we use as a less than 50%, less than 125, basically
less than two for I-C-A-C-C-A ratio
and less than 40 for EDV.
And then once it gets over 1 25 up to two 30, it's
between 50 and 69%.
So the SRU conference chose to
use 70% and above as what would be significant.
And so an I-C-A-C-C-A ratio of anywhere between two
and four is what would be in this category.
And then you can see if it's greater than two 30,
we call it 70, greater than 70% to near occlusion
and greater than four for I-C-A-C-C-A ratio.
And these, and then also the end,
I stock velocity member on the last talk I told you
we would talk about this again.
And if you have end I stock velocity
of greater than a hundred, then also you need to
think about a greater than 70% stenosis.
So I'm sure in your labs it's gonna be like ours
where we really don't do a lot of angiography anymore.
In my institution we have several
accredited vascular labs
and the vascular surgeons mostly I think just go
with ultrasound and occasionally if it's disparate results, they'll do a CTA
or an MRA, but we don't have a lot of correlative data.
So for those labs that don't have a lot of correlative data,
I would recommend that you use this table.
And near occlusion, it's quite variable.
Total occlusion we've already talked about.
So which one to use if you're a new lab,
I would use the SRU criteria at least
until you've had a chance to evaluate
all your correlative data.
And if you're an existing lab, assess the accuracy.
And this is something that the I-C-A-V-L did
when back when we were accrediting with them.
And I thought that was very, very good
because if you are, if you're doing a great job,
go ahead and keep using your standards.
There's no reason to change.
But if you don't have them
or if it's hard to assess your accuracy,
then I would recommend the results
of this multidisciplinary panel.

Carotid Stent Ultrasound Protocol

We are gonna talk for a little bit because protocols and
protocols
and techniques are quick in the carotid.
We're gonna talk about the carotid stent ultrasound
technique back many years now.
Dr. Gary Rubin was one of the earliest adopters
of the carotid stent placement and came to us
and said, look, you know, do you wanna figure out what
if ultrasound is any good in looking at carotid stents?
And I said, you bet. We'd love to do that.
And so what we came up with was
that it should just be a standard carotid evaluation,
but we've added a few things.
So basically standard plus a few things you need
to look at the CCA, you need to look at the ICA, the ECA
and the vertebral artery, just like usual.
But then you also should
you also should look proximal to the stent,
which is typically now in the common carotid artery
because we're gonna be looking for ratios
and pizza stock velocities within the stent
and at places where that stent changes diameter.
So in the stent we look proximal, mid and distal,
and then distal to the stent
because that is an occasional spot
where the stent can collapse.
And so we look at all of these places.
Additionally, we also look at the ECA
because the stent crosses the ECA.
And so at each of those locations in the stint, you look
for peak STO velocity and end diastolic velocity
and look for a ratio
and angle less than 60%.
And again, we haven't really talked about it too much,
but in terms of vascular lab accreditation,
that's very, very important
because that establishes your standards
that you are the same
and have the same great standards as I-C-A-V-L
or American College of Radiology.
And it's very, very important.
And so now that was way back in 97.
So now multiple,
many other studies have been performed
and it's still kind of hard to determine
what is the exact good cutoff to call a stint
re stenotic.
And I think there's a confluence now of agreement
around 70%, that 70%, once you get
above 70% you should consider treating.
And so for that ultrasound criteria
because back in 95, 96 when we were doing this study,
we really only had a couple of stents that steno,
but there's been enough data accumulating now
that it seems like most people are thinking peaks
of stock velocity inter distal
to the stent of greater than three.
And that can be any location in the stent.

Example of a Normal Carotid Stent

So this is a an image of a normal carotid stent.
They're really pretty cool.
You can get really pretty ultrasounds with them.
And this is in the distal common,
but stint.
So the sonographers are gonna be very important in terms
of telling you where they are.
This is,
and you can imagine that
that you've got a big diameter here.
But now we're going into the ICA, so the pizza
of stock velocity, because it's just plumbing is gonna
increase, but it's not likely significant.
This is the proximal ICA or in the bulb actually here.
It's still in the proximal stent.
And then we're seeing in the transverse plane a gray scale
image of the stent and it looks great.
And then we are looking in the ICA
at the stint gray scale
and which is the mid stint
because the stent goes from the common to the ICA
and we're not getting any change any significant gradation here than in the distal
stent, but mid ICA
and then in the distal con
or distal internal post stint,
because that is another place again
where you could have a stent collapse.
So we've looked at all those places
and then also at the ECA to see if that is patent
or if there is a stenosis there.
And that's the normal protocol for a stent.
They're pretty cool. You can usually
get some pretty nice pictures.
And so for example, in this patient
there's an I-C-A-C-C, a ratio of 0.6,
so there's no stenosis here, completely normal.

Example of a Nearly Occluded Carotid Stent

This is a patient with a nearly occluded carotid stent
and we're in the proximal CCA, we're not at the stent yet.
Is there, is this normal or abnormal,
abnormal high resistance flow pattern?
Externalization of the common,
there's probably something not good with this stent.
And you can see in the proximal ICA that
it is nearly occluded.
There's prob maybe a little trickle of flow through here.
And we are looking in the longitudinal plane showing
that we can see jugular, we're in low flow settings,
but we're not seeing any flow in the
stint, which is right here.
And actually looking at the
ECA with the temporal tap.
So we know that
we knew the stint was in the ICA anyway,
but we know that we are, have correct settings
to look for flow.
So we're very, very concerned about this stint.
And maybe it's open because in the mid stint
and distally, we're seeing a little bit of a blip.
If it's open, it's not open for too long.
So that's that is probably the most extreme example
of something that is nearly occluded
but perhaps not completely occluded.

Vulnerable Plaque and Advanced Evaluations

I just wanna show you an image of some vulnerable plaque.
Dr. P*****k showed some nice images of it before.
This was from this week where really there might be a little
bit of ulceration in those patients that have both heart
and soft plaque that's very irregular.
Like this. I always suggest that these patients
that are at higher risk for TIA and stroke
and hope that the physician evaluates them,
at least for aspirin.
And this is interesting
because proximal, there's really not a PTO velocity,
elevation and distal, there's not a PTO velocity elevation,
so there's a nasty looking plaque there,
but it's not, it's not hemodynamically significant,
but it still could be causing TIA and stroke
and see the I-C-A-C-C-A ratios 1.6.
So it doesn't always have to be stenotic to cause problems.

Ultrasound Contrast for Plaque Vascularity

One last thing from the literature.
We have not done at UAB carotid artery ultrasound contrast exams for a long, long time,
but I'm hopeful that this will happen.
There are some reports now of looking at the vascularity
of plaques and this is the money slide.
These two, these are super imposition of the gray scale
and the color or of the gray scale with
contrast.
And you can see that the lumen is
doesn't go all the way up to the wall
because there is a little bit of plaque there.
And post contrast, there are a little blips of contrast.
And so this plaque is being perfused
and we're able to see it with ultrasound contrast.
And hopefully at some point this may add in our evaluation
of which plaques need to be perhaps intervened on,
or at least evaluated further in the patient.
Watch more closely. Thank you.