0:00

So when we look at carotid ultrasound, we are combining two things.

0:04

We're combining what the grayscale images look like and what the plaque assessment

0:08

is with Doppler velocity measurements and other criteria.

0:13

It's never based on just a single number alone. Everything has to play into this.

0:18

So when we have different plaque types, plaque can look different depending on the

0:22

type that's there. So you can have a very soft plaque that has been there for a

0:27

little bit less time. You can have a very heavily calcified plaque that's been

0:32

there for a longer period of time, or you can have mixed, you can have soft and

0:35

calcified at the same time. And this sort of helps explain the ultrasound

0:39

appearance and some of the potential limitations.

0:41

Whereas a calcified plaque is going to potentially have some significant shadowing

0:45

and limit your evaluation, the soft plaque doesn't tend to have that same degree of

0:50

limitation. So these are the standard criteria that we use.

0:54

These are called the NASCI criteria in combination with the Society of Radiologists

0:58

in Ultrasound. And these are the traditional criteria that we used for many years.

1:03

You can see that we form a lot of this based on what the peaks of solid velocities

1:08

look like, and that is our primary driver if we see plaque within the vessel.

1:13

And so if you have no plaque at all, you can call something normal.

1:17

But if you have any plaque, you're going to be calling it less than 50% stenosis,

1:21

and that's going to be based on the velocity.

1:23

And so you can see we have criteria for the 50% to 69% range of stenosis and then

1:28

greater than 70%. Greater than 70% tends to be associated with people who have

1:33

hemodynamically significant stenosis, so that's why we have these different

1:37

landmarks between the two. Now, you can see when we get to near occlusion and total

1:41

occlusion, that's when the things change a little bit.

1:43

So when you get to near occlusion, the waveforms and the velocities are really

1:48

variable because as it gets to a certain degree of narrowing, you can no longer

1:52

increase velocity to compensate for that narrowing, so it starts to become a little

1:57

bit more of a triple flow. And then when you have total occlusion, that's going to

2:01

be more clear. You're going to have undetectable flow whatsoever.

2:04

In 2023, the IAC actually recommended changing some of these criteria and updating

2:10

them, and the reasons were primarily because of the velocity thresholds that they

2:15

were using. You can see here we moved from effectively 125 to 180 centimeters per

2:20

second. This is because they were getting essentially too many false positives in

2:26

that 50% to 69% stenosis window. We can see a lot of those elevations sometimes

2:32

even in patients who have pretty normal-looking vessels.

2:34

So, important to know which criteria your laboratory uses.

2:38

We have switched over to this system, but if you are using the older system at your

2:42

institution, you'll want to be aware of that so you can use them appropriately.

2:49

So just two examples of what some of these occlusive things look like.

2:52

So in near occlusion, you can have what's called a string sign, which is a tiny

2:57

little residual channel of flow. You can see here the waveform that we get is sort

3:01

of a funky waveform. It doesn't look like what a normal waveform looks like.

3:05

You can see it's piecemeal above and below, reflecting that there's very turbulent

3:11

things within that area. You can see you have a normal amount of flow, more

3:15

proximal to this, and as we get down towards this area of narrowing, you can see

3:19

the channel narrows down a lot, and so that's a vessel that was near occlusion.

3:24

And then if you take a waveform up here, you'll see that it basically doesn't show

3:28

any flow. And so that's what we saw here, where we have no color or spectral flow.

3:33

We see nothing on the waveform. Sometimes you'll see just a little bit of noise on

3:37

the waveform that's not a true actual waveform as we look at it.

3:41

And so really the challenge is going to be distinguishing, at times, really true

3:45

occlusion from something that's just extremely slow flow.

3:49

It can be tough to pick up.