Cerebrovascular Ultrasound - How to Do It Well - SD

Introduction

Hi, my name is George Bjo,
and I am the Director
of Vascular Ultrasound Services at Montefiore Medical
Center in New York City.
Today, I'll be going over with you techniques
and protocols for the use of duplex ultrasound
and the evaluation of the carotid arteries.

Most of what I'll be
talking about today has been extracted from the SVU
procedure protocols
and guidelines, which are
available at www.svunet.org.

Today, I'd like to go over the use of
a cerebral vascular duplex ultrasound for evaluation
of the carotid arteries
and go over some basic protocols on how to do it well.

Patient Preparation and History

In the evaluation of any patient, I believe
that it's important to do a little bit of a patient history
and some preparation involving both the patient
and the technologist.

It's always a good idea
to explain the procedure to the patient.
It puts the patient at ease.

We typically like to, what we say in our facility is to
under promise and over deliver.
So we always give the patient the general idea about
how long the examination will take.
Again, it puts the patient at ease
and relieve some of the anxiety associated
with any diagnostic testing.

We believe it's always important to obtain a history
and a physical examination,
at least a limited physical examination in your patient.
And we always do an assessment for risk factors.
We ask questions regarding previous surgeries.
Of course, the primary questions would be questions
regarding any previous carotid endarterectomy
or perhaps carotid stenting in these patients.
Of course, the examination would be modified
to evaluate those issues.

It's always important to elicit a history for symptoms as well as the reason for the referral.
For instance, if a patient comes in with a chief complaint of transient loss
of vision in the right eye
and some transient loss of function of the left side
of the body, we would more judiciously evaluate the carotid system on the
right, of course, because that would be the vessel referable to those symptoms.

It's always a good idea to look at the results
of any other previous tests
that may have been performed in your patient,
and that would include any CTAs, any RAs,
or perhaps any carotid duplex scans from another facility.
And we always look to do a review of any previous studies
that have been done in our own facility.
And that's important because you want to be able
to reproduce the whole situation from the previous examination.
That would include using the same doppler angle,
the same beam angle, and if possible,
if you have more than one piece
of equipment in your laboratory to use the same piece
of equipment on a follow-up study.

We may or may not perform a brachial artery blood pressure.
We do not happen to do that routinely.
I know there are some laboratories that do do that.
We have an algorithm in place that calls
for the performance of a bilateral brachial artery blood
pressure, and of course, any patient who presents
with symptoms referable to the posterior circulation
or any patient of course that's referred
for asymmetric bilateral blood pressures,
would get an evaluation in our lab
and also get an evaluation
of the bilateral subclavian arteries as well.

Indications for Carotid Artery Examination

These are just some of the common indications
for examination of the carotid arteries,
and they include any patient who presents
with transient ischemic attacks.
Any patient who has had an episode of amaurosis fugax,
carotid bruit is probably the most common
indication in our facility.
Any patient with a history of stroke, we would follow up an examination
and any patient with a known stenosis in excess of 50%,
and we do that about every six months or so.

And it's appropriate
to follow these patients up after an intervention.
The most common ones being carotid endarterectomy
and carotid stenting.

We get a few referrals to evaluate the carotids
and the vertebral arteries in patients
with asymmetric blood pressures,
and of course, it's always appropriate
to evaluate the carotid arteries, any patient
with trauma referable to the area of the carotid artery.

Equipment and Instrument Setup

In terms of equipment,
any standard duplex scanner can do the job.
Color flow is not absolutely necessary,
although color flow is probably available on most
of the machines that are out there today.
It does help in identifying vessels,
and it serves as a very good guide for the placement
of the sample volume when evaluating patients with stenosis,
and therefore, it does reduce the overall examination time.

However, I have not yet seen any papers that have shown
that the addition of color has improved
the overall accuracy.
You could probably do just a good scan in terms
of accuracy with or without color,
although color does absolutely serve to help.

In terms of equipment and instrument setups.
We typically like to use the highest frequency
that allows us to see the vessel of interest,
but anything between the range of five
and 10 will do the job and do it well.

In terms of image orientation, we typically orient the image so that the head
or the brain is to the left of the monitor
and the heart is to the right of the monitor.

Now, as you know, in terms of color flow assignment,
any flow color will be set.
So that flow toward the transducer can be either red
or blue in our facility,
and I think by convention in most vascular laboratories,
we typically assign red for arteries
and blue for veins, just for consistency.

In terms of the color box or the ROI,
which would be region of interest, keep in mind
that the wider the box, the slower the frame rate.
So we try to keep the box as small as possible,
especially when we're evaluating suspected stenosis.

And also keep in mind that the color scale
and the color gain really should be adjusted throughout the
examination to evaluate changing velocity flow patterns, as well as to compensate
for the differing depths of all the vessels
that are being evaluated during the examination.
So it's important for the technologist
to make all those adjustments as he
or she is moving on throughout the examination.

Examination Protocol

A complete examination is a bilateral examination
that includes evaluation
and visualization of the common carotid artery,
the carotid bifurcation, the internal
and external carotid arteries, as well
as the vertebral artery.
And again, sometimes the subclavian.
We do not routinely look at the subclavian artery in
our laboratory.
However, if there's some specific indication
to look at the subclavian artery, we will do that.

Now, most of the examination really concentrates on the area
of the carotid bifurcation is seen here,
and the origin of the internal carotid artery.
However, it is important to evaluate the remainder
of the extra cranial carotid arteries as well.
Keeping in mind that indirect findings will sometimes point
you to the area of interest.

Recording Sites for a Normal Study

In terms of recording sites for a normal study,
we typically would acquire 12 images, at least 12 images,
and what we like to refer to as predetermined sites.
And now keep in mind we're looking at the entirety
of the extra cranial carotid artery system
during the examination,
but those images that are acquired would include the mid
common carotid artery, somewhere two to three
centimeters proximal to the carotid bifurcation,
the bifurcation itself,
and at least two measurements within the internal,
somewhere in the proximal portion of the internal
and then further out distally.
We would then acquire an image at the origin
of the external carotid artery and one at the vertebral.
And again, sometimes within the subclavian.
Again, every study is bilateral,
so we're talking about at least 12 images per study.

And also keep in mind that the number
of images acquired will vary according
to the specific laboratory protocols,
which gives me an opportunity now to mention
that every laboratory should have a
written protocol in place.
And this is important because it promotes consistency from
one study occasion to the next.
And also, it's very important in labs
who have more than one technologist on staff, we need
to know that we're doing the same thing from patient to patient.
That's very important. So it's important to have
a written protocol in place.

Imaging Approaches

Now, most of the examination will happen in the long axis with the transducer sagittal
to the long axis of the image.
Keeping in mind that you'll use multiple approaches
for evaluating the carotid arteries
and probably the best approach
for evaluating the internal carotid artery would be the
posterior lateral approach.

Another very important thing is to keep in mind is
that when you're evaluating for plaque content,
you, we typically do that in the long axis.
For instance, in this patient here, we can see here in this long axis image
of the common carotid artery near the origin
of the internal and including the bifurcation
that there's some wall thickening seen here on the far wall
and on the near wall, he has a little bit
of a moderate plaque at the origin
of the internal carotid artery.
And we will probably classify this as a mild
to moderate homogeneous plaque at the origin of the ICA.

And we really use only four
or five words to evaluate plaques.
And those would be homogeneous
or heterogeneous to talk about.
The content of the plaque could be echogenic
or very echo lucent.
And when we talk about the surface
or the border of the plaque,
we talk about the plaque being either very smooth
or it can be irregular.

Another thing to keep in mind is in the acquisition
of your flow velocities,
that really should happen only in the long axis.
I think it's okay to drop a sample volume within a vessel and transverse only to identify
that vessel in terms of whether or not it's the internal
or the external carotid artery.
But the acquisition
of a blood flow velocity really should be obtained only when you're sagittal to the long axis of the vessel.
It's the only way really to know that you're parallel
to the vessel walls in terms of your sample volume.

And the two measurements that we're interested in,
of course, are the peak systolic velocity
and the end diastolic velocity.

Now, in this image here, another the long axis image of the carotid arteries,
you can see here the carotid bifurcation.
This is the origin of the internal carotid artery.
We can see here that we have a relatively heterogeneous
plaque with very irregular borders here,
and this is probably a more dangerous plaque than the one
that we noted previously.

Here's an example of an acquisition
of a blood flow velocity.
Again, we see here long axis image.
You can see the carotid bifurcation to the left
of the image here, the internal carotid artery,
and you can see a color flow jet.
The sample volume has been placed appropriately.
The Doppler cursor is positioned so
that it's parallel to the vessel wall.
We have a 60 degree angle
and the resulting velocity, that's an excess
of about 350 centimeters per second.
And this would be the appropriate setup for evaluating the origin of this internal carotid artery.

Blood Flow Velocities and Angles

Now, in terms of blood flow velocities in a normal vessel,
the sample volume really should be in the center
of the artery with the Doppler angle cursor parallel to the vessel wall.

Now, in our facility, we always make sure
to angle correct to 60 degrees,
and this is particularly important, especially at the origin
of the internal carotid artery, as well
as in the common carotid artery,
especially if you're using an internal carotid
to common carotid artery ratio.

For the evaluation
and estimation of carotid stenosis ranges, it's almost always possible to obtain 60 degrees.
Of course, you never wanna use more than 60 degrees.
In any case, where you are losing,
where you're using a less than 60 degree angle, I believe
that it's appropriate to document which angle that you're using.
And again, this is particularly important in follow up
studies if you're using anything less than 60.

When you're doing a follow up for comparison,
you really wanna make sure to use the same angle during
that follow up study.

In terms of the sample volume gate, which is the width
of the gate, you want to be about one third to one half
of the vessel diameter.
Keep in mind that the larger the size of the gate,
the more likely that the signal will be detected.
However, there is a trade off in terms of eliciting increased noise within that sample.
So I think it's appropriate to open up
that sample volume wide when you're searching
for the highest velocity within this stenosis.
But I think once you find that you can probably decrease it
a little bit to decrease the amount
of background noise within that spectral waveform.

Another very important factor is
to make sure in the presence of suspected stenosis,
that you're obtaining at least two
to three spectral analyses per suspected stenosis, all
of which put the patient within the same stenosis range.
One or two really is not enough,
especially if there's some contradiction about which range of stenosis that patient is in.
So you wanna get at least three spectral wave forms per stenosis.

I just wanted to share this image with you today to show you that sometimes even placement of the cursors for evaluation
of the velocities can sometimes be an issue.
Here we see the cursor set
or the caliper set so that it's at the peak of systole.
This is where you wanna measure that always at the peak.
If you can run an EKG while you're doing an examination, that's ideal.
You sometimes don't have the capability to do that,
but here is the peak
and end diastole should be measured somewhere in this range.

By definition, really it's defined as 100 milliseconds
before the start of the next systolic upstroke,
and we don't expect our technologists to measure that.
However, we do think it's appropriate
to be somewhere in this area.
Diastole should not be measured here or here or here.
It should be right here at the end of diastole.

Profiling the Stenosis

Another very important feature in terms
of evaluating patients with suspected stenosis to is
to be able to profile that stenosis.
And we just wanted to go over an example of that with you.

In this set of four slides.
You can see here on the top left, we are
what I call in the pre stenotic area,
where we're evaluating the common carotid artery proximal
to a suspected lesion right here at the origin
of the internal carotid artery.
With acquisition of this spectral wave form,
we would then move on through that stenosis eliciting the highest
velocity within that lesion.
And the way that's done is by moving that sample volume back
and forth throughout the color flow image up
and down within the vessel
to find the highest velocity within that lesion.

Keeping in mind that this is the velocity
that should be reported to your interpreting physician.
The highest velocity is the one
that will be used in the estimation of the stenosis range.

The sample volume is then moved beyond the lesion
into the area of just immediately
beyond the tightest part of that stenosis,
where you should see a spectral waveform
that looks something like this.
This is what we refer to as post stenotic turbulence,
and you really should be seeing post stenotic turbulence
and any patient in whom you suspect a hemodynamically
significant stenosis.

The absence of this type of a signal
beyond a hemodynamically significant stenosis when it's
suspected, really should prompt you to go back
and really evaluate that area post stenotic turbulence will almost always be present when
you're looking at a patient
with a hemodynamically significant stenosis.

And then we see here that we've moved the sample volume well
beyond that area of stenosis to get a look at
that distal internal carotid artery waveform.

Sometimes the degree of spectral broadening
and occasionally the presence
of a tardus parvus waveform way out
beyond the stenosis will give you an idea about
the severity of that lesion.

So this is what we refer to as profiling the stenosis
to elicit the highest velocity within the stenosis,
and to confirm the presence of a true stenosis
by demonstrating the presence of post stenotic turbulence.

Patient Positioning and Access

In terms of the examination itself, we like
to test our patients on the examination table
with the patient's supine.
As you can see in these images, it's okay to examine the patient by standing up and facing the patient,
or you can sit the patient's head, I think either one is okay,
and I think you should do whatever you feel most
comfortable doing.

Of course, access is important.
You need to remove any tight sweaters
or chains that don't allow you access
of the carotid artery system from the level
of the clavicle here at the base of the neck,
all the way up to the angle of the mandible,
you really need to have access to do this study well.
So if there's any tight sweaters
as the turtlenecks, we remove those.
And of course, you wanna be doing both sides.

We always start the examination
by evaluating the right side first.
We'll turn the head slightly away from the right toward the
patient's left, and we like to have the chin pointed up.

A little bit of a technical tip here In patients
with very short necks
or very high bifurcations, you can sometimes put a little pillow
underneath the shoulders,
and that will hyperextend the neck to give you more access to the distal internal carotid artery.

Transverse Sweep

Now, we start off every examination with what I like
to refer to as a transverse sweep.
And this is just a short access sweep
that starts at the base of the neck
and then works its way up to the bifurcation
of the carotid artery vessels.
And we do this because it gives us a nice preview
of the extra cranial system.
It allows us to get an idea about the location of the bifurcation.
In some patients, it will help you differentiate the
internal from the external carotid artery.

It will, if you put your color on,
it will very quickly allow you to assess for a patency
of the common carotid artery branches by the presence
of color within those vessels.
And it also allows us an opportunity
to note any extra carotid pathology, particularly the thyroid.
And in patients with plaque, it allows you to determine the location as well as the extent
of plaque burden within the carotid arteries.

Evaluation of the Common Carotid Artery

Every examination, of course, starts out with an evaluation
of the most proximal common carotid artery.
Now, on the right, because of the anatomy and
because of the presence of an innominate
or brachiocephalic artery, you can almost always see
or image the origin of the common carotid artery.
And when you can, I think it's appropriate
to go down there and look.

So we image the proximal common carotid artery,
and we look at the flow wave forms.
This is used to determine for the presence
of proximal disease.
Keep in mind, especially in patients with very focal
and moderate levels of disease who have symptoms referable perhaps
to a stenosis at that region.
If you're too far downstream, you may in fact miss
that lesion because the flow wave forms tend
to normalize the further you move away from a stenosis.

So if you can get a very proximal in these patients, you
or you're likely not to miss those lesions.

Disturbed flow is not uncommon because of the proximity to the heart in these patients.
And of course, it may be a more prominent on the right,
because you can get much closer to the origin on the right.

I think the important thing in these patients is to look
for side to side asymmetry in terms of both the velocity the waveform and the size.
And while I'm on that topic, keep in mind
that within the carotid system, asymmetry is very important.
There really should not be much difference between the right
and the left carotid arteries.
Although you may note the difference when you're looking at the vertebral arteries.

So the evaluation of the common carotid artery, again,
starts out at the origin.
Another reminder is
that we should be evaluating the whole length
of the carotid artery system using all the tools in your toolbox.
And we always use color.

In the old days before we had color, we had to take
that sample volume and step it through
and move that sample volume up and down and back
and forth within the carotid artery system.
However, again, one of the advantages
of color flow imaging is that it allows you to see a wide field of view.
And what we do is we allow the color flow image to tell us
where we need to stop within those areas
of those predetermined sites for evaluation, any area that looks suspicious
by the color flow image really should be evaluated by spectral Doppler in the absence of any evidence
of a flow disturbing lesion
or any other pathology within the carotid system, of course,
we would stop at those predetermined sites to evaluate and to acquire velocities.

But our next stop within the carotid artery system,
then would be the mid common carotid artery, somewhere
that's relatively low in the mid neck, in an area
of the vessel where it's straight
and where it's disease free.

And this is an important part of the evaluation,
especially if you're using an internal carotid
to common carotid artery ratio.
The literature states that that velocity should be acquired somewhere two
to three centimeters proximal to the carotid bifurcation,
again, in an area where the vessel is straight
and where it's disease free.

One of the other reasons to look at this part
of the common carotid artery is
to compare the end diastolic flow velocity
to the contralateral side, keeping in mind
that asymmetry should be noted
and interpreted appropriately.

For instance, the absence of diastolic flow ipsilaterally really should clue you into the possibility
that there may be something going on distally.
On the other hand, if you're looking at a parvus tardus wave form where you have decreased velocities on one side versus the other, you have
to start thinking about the possibility
of more proximal disease.

If you note any areas of flow disturbance
or plaque within the carotid artery system anomalous wave forms,
that really does require an explanation.
And if you do see flow disturbance in the absence
of having been able to detect a high velocity proximal to that, you really need to go back.

So you can explain that finding in the absence of being able
to explain that finding you really need
to qualify your report accordingly.

Distal Common Carotid Artery and Bifurcation

The next stop then would be the distal common carotid artery
and what we like to refer to as the flow divider
or the bifurcation.
And now I know some people may call this the bulb,
but keep in mind that the bulb could be could have involved any portion of the common carotid artery system, including the internal
and the external carotid arteries,
or it may not involve any portion of the carotid system at all.

Now, the bifurcation may be an area that is dilated
and bulbous and it is an area where you may develop disease.
And this is the reason why we like to stop here
and acquire a flow velocity, keeping in mind
that the highest velocity within a stenosis,
if the disease does involve the bifurcation
and the internal may in fact be at
the level of the bifurcation.
And you wouldn't wanna miss that
by reporting out a lower velocity acquired within the
internal carotid artery.

The wave forms at this level may be a little bit
different than those that you've acquired more proximally in terms of the diastolic flow
component, and that's okay.
That's something that we expect
and something we don't get too excited about.
Again, because the disease may be a little bit more severe at the bifurcation.

If the velocity obtained that the bifurcation is higher than
that obtained in the internal carotid artery, then
that would be the velocity that you use in your ICA
to CCA ratio.

It's also important if you see plaque
and disease in this area to evaluate the vessel from multiple views when you're attempting
to elicit the highest velocity within that lesion.

Differentiating Internal and External Carotid Arteries

Now, once we've moved beyond the bifurcation,
it's now very important to be able
to differentiate the internal from the external carotid arteries.
And the primary way to do that is
by evaluation of the wave forms.

Keep in mind that the external carotid artery will have
less diastolic flow than the internal carotid artery.
In normal cases, sometimes tapping on the superficial temporal artery will help in that it causes oscillations within the
external carotid artery.

However, keep in mind
that if you do elicit these oscillations within the
external, you really should go back to the internal
and do some tapping there to make sure
that you're not seeing oscillation
within the internal as well.
If you're seeing oscillations in both vessels,
then this parameter will not be useful.

In fact, the tapping
of the superficial temporal artery really is the least
useful of all the parameters in terms
of differentiating the internal from the
external carotid arteries.

The external carotid artery does have
extra cranial branches.
This is something that you will not see within the internal carotid artery.
So the presence of branches when you're evaluating these patients will help in terms
of identifying the ECA versus the ICA.

However, keep in mind one of the pitfalls is that
if you do not see branches, this does not necessarily mean
that you're looking at the internal carotid artery.
It only means that you're not seeing branches.
So it's the presence of branches that's helpful when differentiating the ICA from the ECA.

The internal carotid artery is usually larger
and anatomically is positioned posterior
and lateral to the external carotid artery.
And typically, in most cases, when there is a bulb,
it will be associated with the origin
of the internal carotid artery.

And here we have just a few images to show you how I evaluate these patients.
In this case. Here on your top left, we'll note two vessels
beyond the bifurcation.
Here is one on the near field and one here in the far field.
And we can see here in this vessel,
which is a little bit further away from the transducer,
we see several branches.
This, of course, would be the external carotid artery.
We can see also that at the origin
of the internal carotid artery, this vessel is bulbus.
Again, some evidence that this would be the internal,
but really the primary way to tell the difference is
by looking at the wave form.

So that when we look at this vessel here the one located more anteriorly, we see a wave form that yields continuous forward flow throughout diastole much more diastolic flow in its
counterpart, the external carotid artery,
which has a sharper peak, much less diastolic flow.

And here in this 2D image without color,
we can see the presence of several branches.
All of this confirming that in fact,
we are looking at the internal carotid artery in this vessel
and the external carotid artery here in the far field.

Portions of the Internal Carotid Artery

Now, once you've determined which vessels you're looking at,
we would then carry the examination out
through the proximal, mid
and distal portions of the internal carotid artery.

And in our facility, we define, we have strict definitions about the determining the portions
of the internal carotid artery.
The proximal ICA of course, is that dilated, typically
that dilated area just beyond the carotid bifurcation, usually a one
to two centimeter segment distal to that level.
And this is the area
where disease is most likely to develop.
Keep in mind, this is where most
of the action will happen here at the origin
of the internal, sometimes the carotid bifurcation.

All of the criteria that's out there
and used for estimation
of carotid stenosis has been validated for disease
that involves the internal carotid artery.
At its origin, it's not applicable
to the external carotid artery.
It's not applicable to the common carotid artery
or to the distal ICA,
although it is important to look at these vessels.
The stenosis criteria really should be applied only
to the origin of the internal carotid artery
and sometimes the carotid bifurcation.

The mid internal carotid artery.
Of course, the examination is carried on throughout the
whole portion of the extra cranial carotid,
but we define the mid portion of the internal carotid artery
as that area about two cms beyond the bifurcation, typically beyond that dilated area, the vessel walls tend
to be straight and tend
to be a little bit more normal diameter.

In some cases, disease may extend out into this area,
but in my experience, it's unusual to find a patient
who has disease that involves only the mid
and distal portions
of the internal carotid artery in the absence
of disease in other areas
of the extracranial carotid artery vasculature.

And this is important because you don't wanna make the
mistake of diagnosing a high velocity as an atherosclerotic plaque in the
absence of plaque in other places.

Now, you can absolutely have pathologies out in this area,
typically not referable to atherosclerosis,
especially again, when there's no disease anywhere else.
But for instance, if a patient comes in
after a car accident and maybe has a seatbelt injury
or has some trauma to the neck
where you're eliciting a elevated velocity in this area,
it's more likely to be a traumatic injury such
as a dissection or
an intimal flap rather than an atherosclerotic lesion.
And this does make a difference in terms
of treatment for that patient.

The examination is then carried out through the distal internal carotid artery,
and that is that segment that's at least three centimeters
beyond the carotid bifurcation.
Again, this is an area where atherosclerotic disease is not
usually seen, although you can encounter other pathologies.
Most commonly things like fibromuscular dysplasia.

It's not uncommon to see loops such as you see here,
or kinks or coils.
Occasionally you see these s-shaped tortuosity,
and when you see these tortuosity kinks
and coils, they can all result in difficult angles
for evaluation and therefore artificially
or artifact elevated velocities.

And typically, what I would do in the evaluation
of these patients when trying
to elicit flow disturbance, if I suspect
that there's pathology is I'll use a zero degree angle
and just step that sample volume through the whole portion
of this part of the internal carotid artery to look
for flow disturbances, potentially the presence
of post stenotic turbulence.

But keep in mind, again, it's unlikely
that a flow disturbance in this area will be referable
to an atherosclerotic lesion, and
therefore your interpretation needs to state that accordingly.

External Carotid Artery

Accordingly, we would then complete the extra cranial carotid examination
with an evaluation of the external carotid artery.
And that flow velocity signal really is obtained
at or near the origin.
Primarily it's used to distinguish that vessel the ECA from the internal carotid artery.
And we do that primarily, again, based on the shape
and morphology of the wave form,
which should differ from the internal carotid artery.
As I've already described.

Vertebral Artery

The examination then is taken out to the vertebral artery.
And the best way to identify this vessel is really by straightening the patient's head out just a little bit,
using a very anterior approach to
identify the common carotid artery,
and then angling that transducer laterally,
where you'll usually be able to identify an image such
as this one where we can see the vertebral artery body,
the spinal process, and then the vertebral artery again,
and this is a classic image for the vertebral artery.

We would probably evaluate the vertebral artery somewhere in this area using the
appropriate doppler angle to assess for the direction of blood flow.
Keeping in mind that flow should always be moving from the heart out
to the brain in this image from your
right to your left.

So we would set the color scales and the color direction appropriately,
and look for flow either moving towards
or away from the transducer.

Now, if you suspect a stenosis
or some atherosclerotic process to be going on in the vertebral artery, which is not common,
but can't happen, typically
that will happen at the vertebral artery origin.
And the best way to define that
and identify that is first
by finding the vertebral artery in the mid neck
and using the color flow image to allow you
to work backwards to its origin
and then evaluate the vertebral artery origin for the presence of stenosis.

This is a typical vertebral artery waveform.
It will somewhat mimic that or be a combination really of the common
and the internal carotid arteries.
It should be low resistance
because it feeds the brain directly through the basilar artery of both vertebrals come together.
So really, you should be seeing a sharp up stroke,
which again, you should see in all vessels within the carotid system in the absence
of significant proximal disease,
but lots of diastolic flow here.

In this case, we see a series of various wave forms.
And it won't be uncommon to see something like this here
where you, on your top right.
It's a waveform that referred to as a systolic
hesitation where the peak in fact
of the waveform is displayed below the baseline.
And this is the type of waveform
that you might see in a patient with a latent steal.

These patients who present
with subclavian steal syndrome, which would be an indication
to look at the subclavian arteries.
And really this is a phenomenon that occurs in patients
who present with proximal subclavian artery stenosis proximal to the origin
of the vertebral artery.

So that what happens is, is the heart pumps
and it pumps out the blood.
The flow will traverse up the contralateral vertebral artery
around the horn,
and then move in a retrograde fashion down the ipsilateral vertebral artery
to perfuse the ipsilateral upper extremity in the presence
of the subclavian artery stenosis,
which is no longer able to perfuse the arm.

When you see these patients,
they often will come in with asymmetric blood pressures
or symptoms referable to the posterior circulation.

The peak incidences in patients who are between the ages of 40
and 60 years, males outnumber females two
or three to one, and it can also be seen in patients younger
than 30 years of age in patients
who have Takayasu's disease or giant cell arteritis.

Now, these patients can come in
and demonstrate various vertebral artery flow pattern changes, usually consistent with the degree
of disease within the subclavian artery,
and in fact, may have a normal waveform at rest
or can yield systolic hesitation.
They can come sometimes present with an alternating waveform
or may just come in with complete reversal when the stenosis
within the subclavian is very severe.

Now, in patients in whom you suspect a subclavian steal syndrome who present with normal wave forms,
we can do postocclusive reactive hyperemia testing.
And this is very simply done
by placing a blood pressure cuff on the ipsilateral arm
and inflating that cuff
to a supra systolic pressure while monitoring the flow changes within the vertebral artery.
After three minutes or so, that cuff can be deflated.

Of course, we're creating a hyperemic response here in the
ipsilateral upper extremity.
And if that's subclavian stenosis is significant,
the flow within the vertebral artery will reverse some patients, if they can.
You can allow them to exercise while evaluating the
changes in the vertebral artery.
And again, if the subclavian artery stenosis is
hemodynamically significant,
you really should see some changes within the vertebral artery.

Subclavian Artery and Related Symptoms

Again, these are some of the symptoms associated
with vertebral artery disease.
Posterior circulation symptoms include dizziness,
drop attacks, lightheadedness, visual disturbances,
and these are a few of the other symptoms associated with patients with this type of disease.

When they present, you really should be evaluating the
subclavian artery.

Now, of course, a normal subclavian artery will yield tri or biphasic flow depending on the vasomotor tone.
Typically high resistance in nature, all vessels again,
should have a sharp upstroke and a systolic peak.

When disease starts to set in,
you'll see an increased velocity
and turbulence with increasing turbulence with greater disease severity.

Often these patients in very severe forms
of the disease will present with delayed systolic upstrokes
and rounded peak velocities.
And then the end stage manifestation in patients
with occlusion would be this very blunted sometimes tardus parvus wave form.

Conclusion

Now, that's the evaluation of the patient
with carotid artery disease in terms of the use of carotid duplex ultrasound.

If you want more details about these professional
performance guidelines, I would refer you to SVU's website.
That's www.svunet.org.

And very soon we'll have some DVDs that will also go over the technical performance of these examinations.

Thank you very much. I wish you good luck
and happy scanning.