Basic Carotid Interpretation

Introduction to Basic Carotid Interpretation

We are going to talk about basic carotid interpretation, and we're going to talk about everything that there is to know.

Really, you could probably stop after this and you'll know everything that there is to know about carotid ultrasound.

But of course there are some fine details.

But this gives you the theory so that you can apply the hemodynamics that we're gonna talk about to any situation that you should be able to see.

We're gonna talk about theory, we're gonna talk about what to think about in every segment.

We're gonna talk about diagnostic possibilities, pearls and pitfalls.

Normal Aortic Arch and Carotid Anatomy

This is just to remind you of the normal aortic arch, and you have the brachiocephalic artery here, and the left carotid, common carotid comes off of the aorta.

There are variations, of course, left subclavian comes off with the vertebral artery.

This is a normal carotid artery cartoon.

And we're gonna talk about plumbing in this talk.

Flow Reversal in the Carotid Bulb

This is a power Doppler image, and it reminds me of something that Dr. Pollock's already mentioned, that there is flow reversal in the bulb.

So here's the common carotid artery and the flow.

Once it hits this, you get the bifurcation, and once it hits the bulb, it's a bigger area.

And that blood is gonna fill up that entire bulb.

And some of it's gonna reverse, and that's what is the black area here.

Very difficult. Before we had color and we'd put spectral doppler in and say, what the heck is going on?

This flow seems to be reversed. Is that abnormal or not?

The addition of color was a major improvement in our ability to evaluate what's going on.

Plumbing and Hemodynamics Overview

It's all plumbing, and I am looking at this from an engineering point of view.

What goes in, comes out.

I think the plumbers among us would say, yeah, this is all just easy.

When you think about it, the brain wants blood flow at all times, that's really probably a good thing.

So that is low resistance flow through systole and through diastole.

And consequently, this is what that's gonna look like.

You're gonna have a very sharp upstroke, and then you're gonna have a lot of diastolic flow because your brain wants you to keep thinking even when the heart is relaxing.

Brain vs. Face: Low vs. High Resistance Flow

The face, however, doesn't care those muscles in the face, even when you're speaking, can still keep going without much flow.

So this is a very high resistance pathway.

And this is what the flow looks like.

Again, a sharp upstroke, but very little diastolic flow.

Does that make sense? The common carotid is a combination of a low peak cysto velocity flow or a low resistance flow, and a high resistance flow.

If you have no, or a low degree of stenosis, you're gonna have high resistance in the ECA low resistance in the ICA.

And what are you gonna see in the common for the waveform?

A combination, right? It's gonna be low.

Focal Stenosis and Spectral Broadening

All right, when you get a focal stenosis, then we've got flow coming in.

There's a narrowing.

So the blood, in order to get the same amount of blood through, it has to speed up in that valley and in that tight little area.

And then afterwards, once it speeds up, then again there's some dilatation.

And the blood fills that whole lumen.

And now you've got disturbed flow, you've got a wider range of velocities, and there's we look at that as spectral broadening.

Before you could have drawn my spectral waveforms with a pencil, and now you draw them with a big magic marker that's got a thick tip.

And that's really what that looks like.

And you know that all the velocities are not in a laminar flow.

There's multiple different velocities traveling in that pipe.

High Degree of Stenosis

All right, now we have a high degree of stenosis in the ICA and we may have some turbulent and we may have some increased diastolic flow.

I'm gonna talk about that in just a second.

But first I'm gonna show you my absolute favorite slide of all time, honestly.

And it's flow hemodynamics.

This peaks this dog. Here's peaks this dog velocity on this axis, and here's the diameter stenosis on this axis.

And you can see peaks this dog velocity hums along, doesn't change really at all until about 50 to 60% stenosis.

And then all of a sudden, the peaks dog velocity goes up.

Because if you think about a tunnel or an area of narrowing, in order to get the same amount of blood flow through, you've got to speed that blood flow up.

It's just like if you see a rapids, when I go to a park, that's what I end up doing is taking pictures and of narrowings and rapids, because it's the same thing only in nature.

This has peak diastolic velocity.

And we'll see this again, it doesn't rise up quite so much until 60, 70%, but then it's over a hundred peaks centimeters per second at about 70, 75.

So once we end up with quite a significant amount of stenosis, the diastolic velocity goes up as well.

And this is another way to look at it.

This is ed blue data, and if you look at the systolic velocity ratio, that ratio also goes up around 50 to 60%.

Given the fact that I've shown you just now multiple different ways to look at this, you can conclude that there is no one way, no one number that you can use to evaluate this plumbing.

And that is something you can take home to the bank.

But we are so we have to look, use peak systolic velocity.

We have to use systolic velocity ratio, and we also have to use diastolic at some point as well.

Scenarios with Occluded Vessels

Occluded External Carotid Artery

If we have an occluded external carotid artery, and we have the ICA, that's low resistance flow, what kind of waveform do we have When we are looking in the CCA, which is the first place we look, never look at the ECA or ICA, we always look at the CCA first low resistance flow, right?

That's what we're gonna see.

In the CCA, we always look there because we're gonna be able to say, we're gonna start being able to figure out what's going on downstream by what we're seeing upstream.

All right? Who cares? You know, ECA?

Well, the point is, is that you need to make sure that it's not an occluded ICA.

And I remember the first time that I was moonlighting and was the radiologist who had to make that determination?

Was it the ICA or was it the ECA?

And this particular patient had an occluded ICA on one side and then a high stenosis on the other.

And if he was, if he had a high PTO f he turned out to be ICA that was nearly occluded on the side, then he was probably gonna end up in the hospital.

And if it was an ECA, we wouldn't really care.

Well, the ICA doesn't have branches and it doesn't have a temporal tap.

And we'll talk about temporal tap in a minute.

Occluded Internal Carotid Artery and Externalization

If we have an occluded ICA, the ECA has high resistance flow, the ICA is occluded.

So what are we gonna get? What kind of waveform are we gonna get in the CCA high resistance flow?

And that's what's called externalization of the CCA.

We'll commonly see that.

If this ICA has been occluded for a long time, you may get enough collateral flow into the ECA that then it has a more low resistance waveform.

But in the acute setting, you're gonna see this high resistance flow with an occluded ICA.

And again, we're gonna talk about trickle of flow in a minute.

Trickle Flow in Stenosis

This is exactly what Dr. P*****k showed.

You know, we all think of the trickle of flow just like this, that that stenosis that extends from the bulb into the ICA is just terrible all the way to the skull base, and it's really not true.

We think about that because of the contrast that we give on angio is in the it is heavier than the blood, and it just pools in the dependent portion of the vessel, which is the posterior.

And it looks like there's a string, but it is important to exclude patency.

And the reason for that is because you can do an endarterectomy and a patent ICA, but you can't do it on an occluded one.

Here's what it could look like, and this is what it usually looks like that you have just a lot of plaque around the bulb and really not a huge amount more distally.

Remember that.

Occluded Common Carotid Artery

Now what if you have an occluded CCA and an ICA and ECA no flow, right?

That's easy. And we see that at least once every year or two, surprising how these people can still be alive.

But you know, we see that we've seen icas that are occluded on both sides, and the people are still sitting up talking to us.

Well, occasionally we'll see this.

And usually the sonographers that are training are the people that get these.

It's rather unfortunate.

And they come in very confused.

Either that or totally elated because they figured it out, and you'll have an occluded CCA.

But the ECA is keeping the ICA open. How does that happen?

The ECA reverses the flow reverses in the ECA from collaterals.

And you end up going in the ECA, which is retrograde, and then up the ICA.

It's very confusing, but once you figure out, it's a really cool.

Approach to Carotid Ultrasound Examination

Let's talk a little bit more about what to think in each segment.

I've already alluded to the fact that you really need to start with the common.

You can't just go to where the money is because if you go to where the money is, which may be the ICA or ECA, you could be confused.

So I always, when I approach an ultrasound, especially a carotid, I always look at it the same way.

The first thing you have to do is assess the common crowded artery waveform.

If it is 0.2 meters per second, it's gonna be abnormal.

Normal is 0.6 to 1.0.

So first you have to say, is this a normal peak systolic velocity?

And again, that waveform is a combination of the IC and ECA and it also must have diastolic flow.

So you've already learned a lot about the patient.

If it's normal, now this peak systolic velocity is quite low.

And if it's abnormally low, then you need to check if it's a bilateral process, because we do have two.

So if it's bilateral, what do we think? Cardiac, right?

So then we're in a different ballpark then when we're thinking about cardiac, could have low cardiac output, could have aortic stenosis.

And hopefully one of my colleagues will show an example of bi various flow because that does not belong in a basic talk.

But there are some clues that we can use to look for stenosis.

Unilateral Low Peak Systolic Velocity

If there's an unilateral low PTO velocity in the common carotid artery, you need to assess the waveform.

First of all, if it's a low resistance flow, maybe there's a proximal stenosis, remember we can't see down to the arch because the overlying lung.

So, but that occasionally happens, and that's kind of a gray area that we just don't often see, and we don't often think about that.

We always think that it's in the bulb and it's not.

It could be proximal.

If it's a high resistance flow pattern, there's probably gonna be a distal stenosis.

And it is typically in the ICA, but sometimes it may be very distal ICA that we can't even see.

And if there is high resistance flow, typically you've got externalization of the common.

Example: Patient with High Resistance Flow and Stenosis

This is a patient peaks dog velocity is 0.16 meters per second.

Normal or abnormal normal is 0.6 to one.

So very abnormal.

Not really much diastolic flow, maybe a little bit more diastolic flow in the common, but sharp upstroke, not a tars part pattern here.

And peak dog velocity here is 0.1. It's getting worse.

We don't know how this guy's perfu.

Well, when we look, we can expect that there's gonna be some impediment to normal blood flow, which is this high resolution or this high degree of stenosis plaque.

And again, this plaque is soft plaque, not a lot of calcification here.

So this patient could be at risk for increased TIN stroke.

When you put color on, you can see that this is quite narrow.

This is probably gonna be visually maybe greater than 90% we put power on, although honestly, we don't use power that much anymore because our color doppler is so sensitive.

But we will, I will talk about that more on Tuesday.

You can see that these settings are very sensitive.

The lumen probably is not quite this big.

You could not put color on and measure diameter.

You should do that in the gray scale because that's more accurate.

Well, this ICA is 2.55.

So we have a ICA to CCA ratio of 26.8.

And by any measure, that is very abnormal.

And I would say even though it's in the 80 to 99%, I'd put it in the greater than 90% category.

Ratios and Measurement Techniques

Now, it's very important to realize that all the ratios and all the numbers that I'm telling you about and that we'll talk about in the next talk in terms of actual numbers that you should use in your lab, those are based on ICA to CCA ratios.

Those are ICA. It's not c, c, a.

So if you see something in the CCA, you have to use a different technique.

You can't use the ratios that are developed for the ICA.

Blood is flowing in, blood is flowing out, and it's beating up at the stenosis.

And you take the pieces Ps, dog loc, velocity in at B, and you compare it to a, and this is in the common that you use this ratio.

And then you use the ratio of B, the highest, the highest PS dog velocity to a, an upstream velocity.

And this is a pretty common ratio.

You'll see that in bypass grafts.

We'll see that in fistulas and grafts on Tuesday.

And actually it's what we learned in medical school before or in residency before we got all these new crowded artery standards.

Tandem and Multiple Stenoses

If you have a tandem stenosis, then you need to use a pizza stock velocity ratio.

And in practicality, really everything that's over 50% is between two and three.

If it's over two, it's probably significant.

We would like to be able to break it down into greater than two to three is greater than 50% and greater than three is greater than 75%.

But it can be very difficult to do that in part because a sonographer, once they get a very high peaks of dog velocity, they might quit and not get the absolute highest peaks of dog velocity.

'cause you know, you've got a significant stenosis.

If you have multiple stenosis, remember the pressure drop from the stenosis is highest in the first stenosis.

So the second stenosis, you really might not get a huge ratio.

And then you really have to go more with visual diameter reduction.

Thankfully this is that's pretty uncommon.

But this is an example of a common carotid artery stenosis in the distal common carotid artery.

So we look proximally and that's 83 centimeters per second.

And then distally, just at or distal to that stenosis, we get 235 centimeters per second.

So that is a ratio of 2.8 and that's greater than 50%.

So then the question is, do we need to deal with that common carotid artery ratio?

'cause there sometimes it's significant in the common as well.

External Carotid Artery Assessment

Let's talk about the external carotid artery.

Again, I already said we don't really care about it, but we really need to assess it to differentiate it from the internal carotid artery.

So you need to do that with the temporal tap and also to determine a cause of brewery.

And I'm very complimentary to the clinicians that still listen to the breweries.

And if they have gone to the bother of listening, I trained at Mayo, if they've gone to the bother of listening to the neck for a brewery, I wanna say good job.

It's because of this.

It's either a torturous aor aor, a torturous carotid.

It is an ICA stenosis or an ECA stenosis.

I wanna say good job.

This is what it's from, I think.

Normal ECA Waveform

This is a normal ECA waveform, again, very different from the ICA waveform high, quick upstroke, but very little diastolic flow.

The ECA has branches.

Very rarely will you see an ICA that has branches.

The ECA is typically medial and anterior, which is towards the face.

But you can't bet on that you have to put doppler on it.

You cannot just use the physical position of the ECA.

And again, the ECA typically has high resistance unless there's a significant ICA stenosis with collaterals.

Temporal Tap Technique

If you don't get, if you already know everything else, this may be the one slide that you learned something from or the one topic, the temporal artery is a branch of the ECA and you need to tap anterior to the mid ear right here.

Look at the mid ear, go right anterior, do it.

You might not be able to feel it, but go ahead and tap there anywhere anyway.

That temporal artery will then, as it's connected to the ECA, have reverberations and those reverberations will go into the ECA.

If there's no stenosis, you might see it in the ICA as well, and you can't let that confuse you.

This is a normal temporal tap.

I consider a temporal tap, a mandatory part of every carotid examination.

If I see that on the outside examination, I know that the stenographer as well trained and they've got a accredited laboratory, or more than likely they do.

These are the little waveform changes that you see when you tap very quickly on the temporal artery.

What's useful about this is that if there's only one stenotic vessel, which is really common and you're unsure which artery it is, this is the test that you use to determine which artery is the ECA and which one is the ICA.

This first part is for the visual people.

If you have a ECA stenosis, the you tap up here, you're gonna see the tap in the ECA, but the stenosis is so high that it's not gonna get transmitted into the ICA.

Does that make sense? This requires thinking about, okay, now we've changed, we've got an ICA stenosis, here we go, we've tamp, we're tapping in the ECA.

So we see it in the ECA, but this stenosis in the ICA now is so high that we don't get it transmitted into the ICA.

For the graphical people in the audience, this is what I just said, only graphically if it's normal, you're always gonna see the temporal tap in the ECA, you may or may not see it in the ICA.

If you have a significant ICA stenosis, you're always gonna see the temporal tap in the ECA and you're not gonna see it in the ICA.

If you have a significant ECA stenosis, you're always gonna see it in the ECA and not in the ICA.

You're always gonna see the temporal tap in the ECA.

That's how you can tell which vessel is the ECA, very important and very helpful when you're gonna make a tough call.

Internal Carotid Artery Evaluation

Let's talk about the internal crowded artery that we've already said has moderate diastolic flow because the brain needs it.

And the majority of the plaque, although it could occur in the common, does extend from the bulb to the proximal ICA.

But the stenosis again can be miter distal ICA and even in the skull base.

Mild Spectral Broadening

This is an example of the mild spectral broadening that I talked about before.

You can't just draw this with a pencil.

So there are multiple velocities and it could be because there's a stenosis upstream that we didn't appreciate.

Or sometimes when the vessel dives deeply, you see a lot of disturbed flow.

Irregular Heart Rhythm Considerations

This is a patient with an irregular heart rhythm.

And this is to remind you that there are some techniques that we need to talk about.

You're not gonna wanna take the end diastolic velocity here at the end of a long heartbeat.

You are not really gonna wanna probably take the systolic velocity here either.

You're probably not gonna even wanna take this next beat because it did not go come through a usual pathway.

It may be a little bit higher peak of dog velocity.

You're really gonna wanna look at that vessel at that heartbeat.

That's the one you're gonna wanna measure for peak of dog velocity and dys dog velocity.

Stenosis Evaluation Methods

Stenosis evaluation, there should be a visible narrowing and we measure peak dog velocity and diastolic velocity at the stenosis.

If there's overlying plaque such that we can't see that stenosis, then you look at the distal jet and measure the peak dog velocity and DTO velocity in that jet.

Here's the difference between the radiologists and the cardiologists.

The radiologists all angle correct with the angle of the jet because we do have that capacity.

The cardiologists typically like to keep it at 60 degrees and there's quite a bit of variability.

I talked to Kirk Beach about it was who was in strand's lab, and I kind of get a little bit mixed answers as to how exactly it was always done.

I know that in some core labs they actually do angle correct if you don't have it at 60 degrees.

Patient Examples

84-Year-Old Male with Syncope

This is a example of what I have shown you.

An 84-year-old male with syncope and his right common carotid artery peaks, his dog velocity is 0.5, so 0.48.

So a little bit on the low side.

And when we get to his bulb, there's a stenotic vessel there.

Which one is it? And how do we tell?

Visually we think that it's gonna be ICA 'cause normally that's the one that's significant.

And when you put peaks of dog velocity here, you've got a low diastolic flow and a high peak systolic velocity and the I-C-A-C-C ratio of 2.5.

And again, I'm gonna talk about standards in the talk after this one.

Our peak systolic velocity is not elevated by most standards, but the ratio is because our overall peak systolic velocity in the common is lower than usual.

That's one of the reasons why you have to take a ratio.

You can't just go by a peak systolic velocity.

Another Patient: Bilateral Comparison

This is another patient peak STO velocity.

In fact, this may be the other side.

Peak dog velocity 0.3, yes, it is the other side.

And here's this bulb. Is there a stenosis there? No clue.

But I can look at the jet distal to that and I get a peak dog velocity of 1.57.

And my ICH to CCA ratio there is 5.2.

So this side is worse than the other side.

What side do I fix next?

Or do I fix them both at the same time?

Generally, we don't fix both at the same time.

And one of the reasons is because there could be an artificial elevation of the peak sto velocity on the contralateral side because of that high degree of stenosis.

If you have one side that's got a really high degree of stenosis, most of the blood flows come through the other side.

And you could have an artificial elevation.

So again, peak stock velocity is not really high, but there's a high grade stenosis by ratio.

In this case, if you wanted to, you could just go with the ultrasound.

But in general, or you could consider a CTA or MRA, most of the time we would just do the ultrasound, start with a left end art ectomy or put a stent, whatever your lab does, and then reevaluate.

67-Year-Old Woman with Right-Sided Stroke

All right, this is another patient, 67-year-old woman with a right-sided stroke and looks good, doesn't it?

We always do gray scale first, and I don't see a thing I, it could be a little bit brighter.

The scale could be a little bit brighter, but I don't see a whole lot.

So it looks widely patent.

But then when I put a doppler in there, look, that peak of salt velocity is low, it's 0.46 and it's also high resistance flow.

What's going on Distally, I'm expecting that there's a high grade stenosis here.

And this is the ICA, it looks like it's nearly occluded, really low flow.

So a significant distal stenosis.

And this is this patient, she's already had a stroke, they decided not to do anything with her.

And this is six months later, again, we see externalization of the common carotid artery waveform.

ECA has. Here's the temporal tap.

We know it's ECA, not very much diastolic flow.

There's still, so we have externalization of the common and now you, it's barely showing up, but you put color on.

Now we've got an occluded versus trickle of flow.

And here it is in the transverse view, just off the bifurcation.

And then boom, there's really nothing.

So that high grade stenosis that we had has now worsened and now there's thrombus in the ICA all the way, all the way up nearly up to the bifurcation.

Pitfalls in Carotid Ultrasound

All right, so one thing that you need to know before you call a IC stenosis check again, you know, ultrasound is a very busy place.

Our volume is up 8% for the first couple of months of this year.

We're always doing more with the same amount of stenographers.

And sometimes at night, they're the only person on there if they get up to answer the phone.

They might do that three or four times during an examination.

And before you call that stenosis, make sure that the ICA and ECA waveforms are not identical.

This is a pitfall that we have fallen into a couple of times.

And the first time actually we did fall into it thereafter, we did not fall into it.

We recognized it. And basically if you had an ICA occlusion, the you could call the first branch of the ECA, the ICA and then just completely mess up the rest of the case.

So this is a patient that had a funny looking carotid bulb and it was a junior sonographer as usual in terms of something odd.

And here's the CCA, here's the ECA and here's the ICA and they're all identical waveform.

I, so one of my more senior sonographers went in and said, you know, I don't know, maybe there's an ICA stenosis or something else going on, and but I'm not sure what vessel you're in even 'cause they're all high resistance waveforms and they're all identical.

Well, the more experienced stenographer found a very low bifurcation, nearly at the clavicle.

And there's the bifurcation and there's this is the ECA again, temporal tap.

And with that low bifurcation, if you kind of slid down as far as you could, you could see that there was a tight stenosis there.

And I think that stenographer was going up the ECA all the way.

So make sure that you're not calling an icea stenosis when your stenographer is having difficulty.

And all the waveforms are similar.

No Flow and Trickle Flow Detection

So when you have a no flow, ultrasound is good, but it's not perfect.

And again, we don't wanna miss that diagnosis.

Optimize for low velocity flow, which we're gonna talk about again in two days.

Look for a trickle of flow if you can.

Ultrasound contrast agents at some point we'll probably be quite useful in this once they are FDA approved.

So this is a patient with a possible trickle of flow.

And the ECA has a low resistive index feeding collaterals.

And this is the ICA very just a thump basically.

So is this open or not? I can't tell for sure.

I see a little bit in the distal ICA, so I wonder if it's open.

Normally, if it's completely occluded, you can't see that, but you just really can't tell.

And we've talked about this i's the diagnosis here.

It's pretty obvious. I don't have to do much.

I mean, I could put doppler on.

I always do put color on, but this is occluded, this common carotid artery.

And ICA and ECA is completely occluded.

Vertebral Artery Assessment

The vert is open on that side 'cause we didn't talk about the vertebral artery.

And that belongs in a standard carotid artery exam.

And the reason that you need to look at that is because it's an important player in the cerebral circulation.

So again, if you assess the waveform and it's high resistance, you have to worry about a distal stenosis or a occlusion.

It could be a hypoplastic vertebral artery as well.

If it's low resistance, you could have a proximal stenosis.

And some labs now are doing angioplasty and possible stent placement of vertebral arteries.

My uncle actually had a vertebral artery stenosis and which progressed and it was a devastating disease.

If you can't find it, it could be occluded, it could be congenitally small, or it could be absent.

Subclavian Steal Syndrome

So what we worry about is vertebral artery steel.

And that's when you have a subclavian artery stenosis and you're not getting much blood flow into the subclavian artery.

And you are stealing from the vertebral artery in the effort to perfuse the arm.

So you need to assess the waveform.

And if it's got an abnormal contour called the bunny sign, then you need to worry about a steel.

And there are different grades of steel that are not frank reversal of flow.

And it took me the longest time to actually see this bunny.

I'm not quite sure about the group that named this, but it does look like a bunny from the side.

Here's their ear and here's their body.

This would be a type one and we don't really, if it's this much, I'll usually call it, it might be just a little bit of a notch then I don't call it, this is a type two where it's close to the diastolic diastolic.

This is type three where it goes to baseline.

And here's type four where it goes below baseline.

So obviously the worse these are the more reversal of flow there is.

And what you can do is use the blood pressure cuff maneuver.

And what we do is we put the blood pressure cuff on inflated over arterial pressure for three to five minutes.

It's not gonna hurt 'em.

A little bit of ischemia is not gonna do anything.

It might make their arm hurt a little bit, but then those muscles are saying, oh my goodness, I need some blood.

So they're gonna be all the capillaries are gonna dilate and you're gonna have hopefully hyperemia and so you need to reassess the spectral doppler after you deflate the cuff.

Examples of Subclavian Steal

This is a patient, this is their right side, it's normal.

This is their left side and there's a type three, type four waveform here.

We put the cuff on and it almost completely reverses.

So then you're gonna wanna see if this patient has vertebral ular symptoms.

Typically dizziness or with exercise.

Sometimes if it's a little old man or a little old lady, it might not make any difference.

But if it's a younger person, or they're having a lot of dizziness, you may need to worry about this.

So this is something that we can find and it's pretty cool.

We actually see this quite a bit.

Here's another patient, right? Vert is fine.

Left foot, there's a type one.

I don't usually for the type ones, I don't usually put a blood pressure cuff on 'cause they may or may not change.

But the other ones I usually do.

This is that patient, that same patient that had just the type one though.

And one and a half years later there's a near complete vertebral artery reversal.

So we can see these progress.

Summary

In summary, we've talked about the carotid and it is far from a basic examination, but it is just plumbing.

And we've talked about the theory, what to think about in every segment, and diagnostic possibilities, pearls and pitfalls.

And you should all now be able to go out and read 99% of these.

Thank you.