Cerebrovascular Protocols - SD

Introduction

Hi, my name is George Bjo and I'm director of Vascular Ultrasound Services at Montefiore in New York City.

And today I'll be discussing cerebrovascular protocols, Interpretation of carotid artery findings, although it's primarily determined by acquisition of velocities to determine percent stenosis range where there is suspected stenosis really is multifactorial and based on many issues.

However, I would submit that consistency and adherence to protocol is paramount, and none of these things can be done well unless you have that consistency and adherence.

Equipment and Patient Preparation

In terms of the performance of the examination, any standard color flow duplex scanner will do the job.

The addition of color does help to quickly identify vessels and very quickly identify areas of stenosis.

It helps in terms of placement of the sample volume, and it definitely does reduce the examination time.

Although there's very little preparation involved for the examination, I think the little preparation that there is is important, in my mind, it's important to explain the procedure to the patient and to put the patient at ease.

It makes for a much more facile examination.

I do believe it's important to elicit the symptoms and or the reason for the referral.

Many times this can point you in the direction of the vessel that's referable to the patient's symptoms, and is quite important in terms of the presence of subtle findings that could be responsible for symptoms, that you wouldn't wanna miss.

Brief history and physical is in order.

We do do a history for relevant risk factors also for previous surgeries.

The two primary surgeries, of course, would be carotid artery endarterectomy, as well as carotid stenting.

You should probably acquire a bilateral brachial artery blood pressure.

Indications for Carotid Artery Testing

These are some of the common indications for carotid artery testing.

Transient ischemic attack, A TIA, amaurosis fuac, carotid bruery, history of stroke, follow-up of known stenosis.

The post intervention up, any patient with asymmetric blood pressures, probably, is indicated and any trauma to the area of the neck.

Reviewing Previous Studies

I do believe it's important to go over the results of other tests, whether they be previous duplex scans in other facilities or, to find out the results of contrast arteriography, or Mr. MRIs or CTAs that may have done, been done previously.

And I believe that this is important, because your report really should be clinically relevant.

And if that requires a comparison to a previous report, I do believe that this is in order.

You should probably review any previous studies, performed within your own facility.

And this is important, because, when you're making comparison to previous studies, I do believe, that it's optimal and you can maximize, your interpretation if you're using the same equipment, on follow-up studies.

And also you should use, the same parameters, for comparison in terms of the Doppler and beam angle, as well as in the assessment of the location of the stenosis where it was documented previously.

There have been some issues, published and documented in terms of the use of multiple instruments and probes, used for follow-up studies.

We know that there's inconsistency in the acquisition of peak velocity measurements, and that this is a common problem when more than a single instrument or a probe is used, especially when different pieces of equipment are used.

Rob Dagel and others showed this in 1990 and published it in the Journal of Vascular Technology.

This is also, seen in a study published by Kimmy Smith in the Journal of Radiology back in 1990, where she showed an average variation in the acquisition of the peak velocity measurements taken from multiple instruments that ranged up to 23%.

So, probably optimal to use again, the same, piece of equipment and the same parameters for follow-up studies.

Acquisition of Blood Flow Velocities

The acquisition of blood flow velocities, of course, is paramount.

By convention, we placed a sample volume within the center of the artery with the angle cursor parallel to the walls of the vessel.

We insist at least at Montefiore, that the, technologist sonographer angle correct to 60 degrees.

The gate and a normal vessel should be open to about one third to one half of the vessel, diameter.

Keep in mind that the larger the gate, the more likely you will be to pick up a signal.

However, the trade-off, is increased noise and the potential for spectral broadening.

Within stenosis, we like to see at least two to three, spectral wave forms, within that stenosis, all that fall within the range, the same range of, stenosis.

There have been some issues in terms of use, the use of multiple Doppler angles.

We insist on a consistent 60 degree angle.

We know that there are errors associated with angles of greater than 60 degrees, and, I believe that that's well known and accepted.

However, there is some debate about the use of angles between 45 and 60.

Unpublished data have demonstrated significant variation in the acquisition of velocity measurements when interrogating stenotic lesions from multiple angles.

Here you see an example of, one patient, the same lesion e evaluated with four different doppler angles over a span of three minutes.

And this work was done by gene prim many years ago, to the far left using an angle of 46 degrees.

The peak velocity acquired was 180 centimeters per second at 54 degrees immediately to its right.

The velocity is 260 centimeters per second, at 60 degrees, which is the angle that we would ordinarily use.

The peak velocity recorded was 300 centimeters per second, and then at 70 degrees to the far right, which is an angle we probably would never use, the peak velocity recorded within the same lesion is, greater than 400 centimeters per second.

So I think this very clearly demonstrates that there is significant variation in the acquisition of the velocity when multiple different angles are used.

And this is a strong, for me, indication to use a consistent Doppler angle in our lab that would be 60 degrees.

In addition, to the use of the 60 degree angle, it's also critically important that your angle cursor be parallel to the vessel wall.

And this cartoon plate on the left, you can see here the beam angle as it intersects with the vessel wall.

Here the Doppler cursor angle is parallel, to the vessel wall at 60 degrees, and that would be the angle of intonation.

I've seen this done in many labs where the mistake is to set the angle cursor to 60.

However, the technologist or sonographer will often fail to make sure that the angle is in fact, or the angle cursor is in fact parallel to the vessel wall.

In this case, although the Doppler angle is corrected to 60 degrees, the beam angle, in fact, intersex the vessel wall at 42 degrees, and this will result in errors in the acquisition of blood flow velocities.

One of the other things I would caution, you to do is to not put on the color flow, when you acquire your blood flow velocities here, an example of a, carotid artery with a plaque.

And, most people will turn the color on and then place the sample volume.

Here's your beam angle and then the doppler cursor.

But if you look closely, although it's aligned, to the, flow of blood as, determined by the, color flow image, if you look closely and turn off the color, you can note very quickly, that that doppler angle really is not aligned, to the vessel wall, and in fact, really should be aligned, the way the yellow, line there is aligned.

If we remove the original, beam angle, you can see now that we are parallel to the vessel wall.

So I would be, careful and, caution you probably remove, use the color to identify the stenosis, turn the color off, and then sample, the vessel, without the color flow image.

The, placement of the, cursors to determine velocities often, can be called into question.

And just, an example here of where the ang of the, cursors really should be aligned.

Here's your caliper.

Here at peak systole, I often see, issues with the placement of the calipers in terms of the determination of end diastole.

It shouldn't be anywhere along the specter wave from what really at the very end, by definition, 100 milliseconds before the start of the next systolic upstroke.

Here's an example of what clearly is an over regained image, and you might think that this is not the significant, but you can see here on the left that, the image is very bright and significantly over gains.

What we, train our technologists to do is to acquire the spectral wave form, and it's okay to over gain a little bit, but then just, slowly click back and decrease the gain until you eliminate the background noise.

You can see here on the initial, acquisition of the spectral wave form that the velocity is about 400 centimeters per second.

However, when the spectral gain has been corrected to eliminate the background noise, really the velocity is 300 centimeters per second, and that is a significant difference.

So be careful and not to over gain in the acquisition of your spectral wave forms.

Examination Protocol

In terms of the testing, we test all our patients, on the exam table in, a supine position.

I prefer to sit at the, head of the patient.

Most of the sonographers, the youngest sonographers in our lab, like to stand up and face the patient.

I don't think it matters how you do it as long as you're comfortable, when you're performing the examination, access to the vessels of interest is quite important, and we always have our patients remove any tight sweaters or chains that would get in the way of our ability to access the, the carotid arteries in the neck.

The examination starts with the patient's head turned slightly away from the side being examined.

We always start with the right side, and all complete examinations include evaluation of both the right and left carotid arteries.

A complete examination, includes a visualization and interrogation of the common carotid artery through the level of the carotid bifurcation, all of the accessible internal carotid artery, at least the very origin of the external carotid artery, the vertebral artery.

And when indicated, the subclavian artery, these are what we refer to as our pre, determine, recording sites.

Every examination should include spectral analysis of at least the mid portion of the common carotid artery, the level of the carotid bifurcation, at least two points in the internal carotid artery, the origin somewhere beyond that.

The origin of the external carotid artery, as well as the vertebral artery,

Documentation of the study is important.

And you should have some mechanism for documenting your studies, and it should be part of your protocol, whether you acquire hard copy, thermal paper images, or whether you videotape or have a PAC system in place.

It doesn't matter how you do it, as long as you're doing it the same way every time.

At Montefiore, we still videotape our studies and we videotape the, the quote entire study.

What we do is we acquire representative, 10 to 12 second video clips at all of those predetermined sites that I described previously, as well as areas of interest in terms of suspected stenosis or other pathologies.

You should have some mechanism in place, for review of your study.

When the preliminary, findings from the technologists, are called into question by the interpreting physician, typically that's a conversation, to elucidate the findings and resolve the issue.

Sometimes that will include a videotape review to go over the study.

In any case, you should have that mechanism in place.

The carotid protocol really is, composed of the, examination of the bem mode image, examination of the, of the color flow image, and, the primary determinant of, percent stenosis when it's suspected, and that would be the spectral doppler or, bring something to the table.

The very nice thing about the spectral Doppler is that in addition to allowing you to evaluate, the area where you're looking, it can also provide indirect evaluation of other vessels, either, above or proximal or distal to, the site of interrogation.

And this is a nice example, where we have sample volumes placed in an area of the carotid artery, that, does appear to be normal, but you do see significant difference in the wave forms right compared to left.

And, this type of finding in the left should immediately clue you in, to the probability that there's something going on distally, although you're not looking at the distal portion of the, carotid artery itself.

So it does provide very important information.

Transverse Sweep

Every examination starts out with a transverse sweep.

And I think this is important because it does allow you a preview, of the carotid artery system.

You perform the sweep by starting out at the base of the neck and then moving, distally to the angle of the jaw.

It can give you information in terms of the level of the bifurcation, as well as the extent and location of plaque, and in most cases, it will allow you to, differentiate the internal carotid artery from the external, carotid artery.

These video clips, courtesy of Cindy Owen, show how the use of the transverse image will also help you to plan, the, your sagittal plane imaging.

Here, you see the internal, as well as the external carotid arteries and a transverse orientation.

And you can see that it was difficult, to evaluate an image, both vessels within the same plane.

The internal was remote, and, from the external carotid artery.

Here in this, video clip on the right, you can see that although the internal and the external carotid artery are not aligned, quick transition and adjustment of the transducers is that that one vessel is aligned above the other will allow you to get that nice tuning fork image that, everyone likes to see.

So, I think it's optimal to use your transverse image, to plan your sagittal plane and, and again, get a very nice preview, the carotid artery study.

This here now is, an example of the transverse sweep, and here you can see, the common carotid artery at the base of the neck and play that for you.

Here's the common carotid artery of slow transverse sweep to the angle of the bifurcation.

And you can see, where the, carotid artery bifurcated.

You can see evidence that there's plaque within the carotid artery itself, not just within the internal carotid artery, but also at the level of the bifurcation.

So from this very quick, 10 to 12 second sweep, again, you get an idea about the level of the bifurcation as well as the extent and the location of plaque.

Longitudinal Imaging and Specific Arteries

The most of the carotid artery examination is performed in the long axis, with the use of multiple approaches.

The posterior lateral approach is often the best approach for evaluating and imaging the internal carotid artery.

However, keep in mind that in your acquisition of blood flow velocities, it should always be performed with the transducer sagittal to the long axis of the vessel.

The measurements that we're interested in, of course, are the peak systolic, as well as the end diastolic velocities.

In addition to evaluating plaque in the transverse image, we also assess plaques for their composition and texture in the long axis.

And the four words that we use are either homogeneous or heterogeneous in terms of the content and character of the plaque, and then words like smooth and irregular to describe the borders of the plaque.

We stay away from using words like, hemorrhagic and ulcerated.

Those, findings really are not predicted well, by the ultrasound image.

After the transverse sweep, is completed, we would then go back to the base of the neck to image the proximal common carotid artery, and assess the flow wave form.

We do this to determine, for the presence of proximal disease, in the absence of distal internal carotid artery disease that may be causing symptoms.

It's not uncommon to see, less laminar disturbed flow, especially on the right where you're closer to the origin.

So you shouldn't be surprised by that.

I think the important thing here, however, is to look for side to side asymmetry right versus left in terms of the velocity that's acquired in terms of the shape of the wave form, and also in terms of the size of the vessel here.

If you take a quick look at the spectral waveform acquired on the left versus the, waveform acquired versus the right, and you can see that there's a significant difference between the right and the left carotid artery waveform in this type of waveform here in the bottom, really should again clue you in to the probability of significant proximal uh, disease.

The examination is then carried on through from the proximal common carotid artery up to the mid, common carotid artery in the mid to low neck.

Keep in mind that this does not mean that you should just pick up the transducer and drop it in the middle of the neck.

Really the way this should happen is that the transducers should stay on the neck with the color flow image on.

You should slowly work your way up to the mid portion of the common carotid artery using the color flow image, making sure that your parameters are set appropriately, and again, using the color flow, to allow you to determine areas of potential stenosis and flow disturbance that require Doppler interrogation.

At this point in the midcom carotid artery, I think it's important to compare the anti diastolic velocities with the contralateral common carotid artery.

Here in this case, we have an example of a normal, left common carotid artery sharp up stroke, significant amount or normal amounts of diastolic flow.

And when you compare it to the contralateral common carotid artery at the same level, we have a significant difference in terms of the peak velocity, but also much less diastolic flow almost down to zero.

And again, this kind of a finding would be consistent with a more distal, issue.

I believe that it's important for the sonographer to be well aware of the velocities and the waveforms that they're acquiring, and keep an eye on those things throughout the, performance of the carotid evaluation.

Really, this type of examination requires interpretation as you're performing it because you may have to adjust, your, protocols accordingly.

In terms of, the different kinds of pathology that you detect during the examination, the mid to common carotid artery is an important site, again, because this velocity will be used if you are, if you're in a lab that uses the ICA to CCA ratio, determined to determine stenosis of the internal carotid artery.

We'll talk about that shortly.

Any areas of flow disturbance, that are detected must be correlated to the presence of disease.

Here we see an image of the mid portion of the common carotid artery, and as we know, velocities tend to decrease as you move from proximal to distal in the common carotid artery.

We know this to be true.

This is an important, measurement because the mid, to distal common carotid artery again, is the velocity that you'll use in your ICA to CCA ratio.

We acquire that velocity approximately two centimeters proximal to the carotid bifurcation, somewhere where the vessel is straight, and where that, the vessel is disease free.

This is a very good reproducible location, and that's why, it's, been used.

And this was work that was done by Greg Manetta many years ago.

We then would move on from the mid common carotid artery to the distal common carotid artery at the, at the flow divider or what we refer to as the carotid bifurcation.

This can be an area, that, may be dilated or bulbus.

It, it is also an area where you may see disease developed.

We can often see patients who develop disease within the carotid bifurcation that extends into the internal carotid artery.

In some cases, the waveform may differ from the midcom carotid artery in terms of the diastolic flow component, and that's because of the proximity of the bifurcation to the internal carotid artery.

Keep in mind that this is important.

If you have a patient who has disease at the bifurcation and the velocity acquired at the bifurcation is higher than that of the internal carotid artery, you want to use the higher velocity at the bifurcation to calculate your ICA to CCA ratio here.

We have in fact, a slide with five, carotid arteries.

And I, I show this, just to say that we stay away from using words like bulb.

If you look at these five carotid arteries, the carotid bulb is in five different locations.

However, when we refer to the bifurcation, the bifurcation is always at the level, where the common carotid artery divides and becomes the internal and the external carotid artery.

So we stay away from using the term carotid bulb.

And if we're referring to the bifurcation, we refer to the word, bifurcation.

We always examine the external carotid artery, and you should acquire flow velocity signal at or near, the origin of the external carotid artery.

This is rarely a clinically significant area.

However, it is important, to find the external carotid artery because we use that waveform to help us to distinguish the internal, from the external carotid artery.

And the way to do that is primarily by looking at the shape of the waveform.

The, arteries of the carotid artery system all have their own signature wave forms and sounds.

And I'll just take you through an example of the different levels within the carotid artery system.

Here you're seeing the, common carotid artery, and you can see that, this vessel has a sharp upstroke, a sharp peak with a good, diastolic flow component.

Here at the internal carotid artery.

You can see that the peak is a little bit more rounded with lots of diastolic flow.

The sound is a little bit different than that of the common carotid artery here in the external carotid art.

You can hear, that it sounds significantly different, from the flow wave form that we acquired within the internal carotid artery.

The peak is much more sharp than it is in the common, as well as the internal carotid artery.

And then when you hear and look at the waveform within the vertebral artery, it very much approximates that of the internal carotid artery, lots of diastolic flow, and that's because both of those vessels perfuse the brain directly.

It's important to evaluate the waveform shapes of all the vessels that we're looking at, and keep in mind that the internal and vertebral artery should have lots of diastolic flow.

The external carotid artery can be variable in terms of the diastolic flow component.

Sometimes the drops to zero or can have a reverse, flow, component.

In early diastole, the common carotid artery will be a combination of the internal and external carotid arteries.

And if you look at the subclavian, that waveform really should be, multiphasic as it does perfuse the periphery.

All of these waveform should have rapid, upstrokes.

That's true of every waveform that we see.

Anything that's, say typical in terms of its morphology, requires an explanation in terms of differentiating the internal from the external.

If they all look like this, it would be easy.

As we know, the internal carotid artery has no extra cranial branches.

Where you see a branch, you can be very sure that you're looking and confident that you're looking at the external carotid artery.

However, not all of the vessels, appear that way, sono graphically.

So keep in mind that you should look for several, qualifiers.

The external carotid artery, again, has extra cranial branches.

The internal does not.

However, keep in mind that the absence of branches 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 you see branches, you know that you're looking at the external carotid artery.

The internal carotid artery is usually larger, than the external carotid and is located posterior and lateral, to that vessel.

But the primary way that we determine, or differentiate the internal from the external really is based on the waveform shape.

The external has less diastolic flow than the internal, sometimes bulb location is useful.

Many people have relied on the use of the superficial temporal artery tap.

It would caution you, that this can be tricky and can sometimes be, you can sometimes be fooled.

The presence of, of oscillations that occur with tapping of the temporal artery.

Sometimes, you can see, these oscillations within the internal carotid artery.

So pro, I would recommend that you stay away from the temporal artery tap, to help to distinguish the internal from the external carotid artery.

Once you've evaluated, the carotid bifurcation, you then want to move into the proximal internal carotid artery.

Many times that will be a dilated area, just beyond the ICA origin, for, the sake of standardization within our laboratory.

That is a one to two centimeter segment, just beyond the bifurcation.

And this is the area that disease is most likely to develop.

Keep in mind, that when you apply your, interpretive criteria, all of the criteria that has been acquired and that has been validated is for the use of the ICA origin only.

It does not work for the common carotid artery was in validated for that part of the carotid artery system.

It does not work for the external carotid artery.

You shouldn't use it in the vertebral, and it doesn't work for the distal internal carotid artery.

All of the criteria, again, was validated for use and assessment of plaque, at the origin of the internal carotid artery.

Another thing to keep in mind is that the criteria is only good in the presence of a plaque.

So the presence of elevated velocities alone does not mean that you have stenosis.

The criteria is used for the origin of the internal carotid artery where you see a plaque.

Another thing to keep in mind is this flow separation phenomenon that you often see, at the carotid artery origin, where you have this bulbous formation.

You don't want to get too excited about this.

This is a normal finding.

When you see it, this is exactly what you should expect.

And this is demonstrated in the color flow image as this blue area, just opposite the flow divider.

When you acquire your spectral wave forms, this is often reflected, in this, funny sort of looking wave form that you would see, opposite the flow divider.

I recommend to my technologist that when they're at the ICA origin, where this vessel is bulbous, just get closer to the flow divider and present a wave form that you know is representative of normal.

The examination is then carried on through the mid internal carotid artery.

That's that area approximately two centimeters beyond for us.

In our lab, our laboratory two centimeters beyond, the origin of the internal carotid artery, beyond the dilated area.

And at this level, the vessel walls tend to be straight and normal caliber.

Again, this is an area where you may see, some disease.

Typically, at least in my experience, it's uncommon to see disease, isolated to this area alone without disease.

At the ICA origin, the distal internal carotid artery is defined as that segment that's at least three centimeters, beyond the carotid bifurcation.

And this is an area where atherosclerotic disease is not typically seen.

You can't see other pathologies, such as fibromuscular disease.

You may see tortuosity and, and kicks and coils.

It's often, difficult to evaluate, these areas with, the spectral doppler, because we can't use the 60 degree angle, we often will see these S-shaped tortuosity.

And again, I would caution you to be careful, because you can't have steep flow angles that would produce higher, doppler frequencies.

Often this will result in overestimation of the doppler angle, which will give you falsely elevated velocity measurements.

What we do in our laboratory is just simply use a zero degree angle and slowly stepped through, this area, slowly looking for focal areas, of elevated velocity where we see those, you should be suspicious that there's something going on.

However, keep in mind that that is very unlikely that you will, encounter an atherosclerotic lesion.

It just doesn't happen out in the distal internal carotid artery.

You can't have stenosis from other pathologies, dissections, and things of that nature.

Fibromuscular dysplasia, and again, the carotid artery criteria would not be applied, to the distal internal carotid artery where you suspect that there's stenosis.

Waveform Analysis and Differentiation

I believe that it's important to profile that stenosis, and we do that by scanning through the pres stenotic zone, to demonstrate a normal waveform.

Also, walking through, from the PreOn zone into the stenosis, demonstrating the focal velocity change that you should see at the origin of the lesion.

Once you get in the lesion, you should survey the stenotic area by moving your sample volume, back and forth and up and down to elicit the highest velocity, within that lesion, because that's the velocity that should be used in either your cal, the calculation of your ICA to CCA ratio or in your reporting of the highest velocity.

If you use an absolute velocity, it's important to acquire multiple samples and identify the highest velocity, and keep in mind that the highest velocity may in fact be beyond the most narrow, the most narrow appearing area, whether that is by the two DB mode image, or by the color flow image.

And again, that underscores, the need to really profile that stenosis.

Here we have four images of exactly that.

And your top left, you can see the sample volume proximal, to the lesion.

In this case where we have a normal, common carotid artery wave form, you see the focal elevation and velocity that should be present, within the lesion itself.

This posts stenotic turbulent signal, that is normal beyond, a hemodynamically significant lesion.

And then the distal wave form, way out into the internal carotid artery.

Beyond the stenosis, posts, stenotic turbulence is an important term.

The presence of post stenotic turbulence verifies a true stenosis.

It also defines the distal extent of the lesion.

Of course, you should be careful of normalization of the doppler wave form.

Well out beyond the lesion, and this is why it's important to profile the stenosis.

Don't just simply go out into the distal internal carotid artery and, be fooled, by the presence of a normal waveform and interpret that as a normal finding.

Always step through that vessel, profiling the stenosis, acquiring the peak velocity, the maximum peak velocity, and then demonstrating the post s stenotic turbulent signal that should be present in the, presence of a significant stenosis.

Vertebral Artery Evaluation

Finally, you want to evaluate the vertebral artery.

And I know sometimes, technologists have, some trouble identifying that vessel.

What I do is simply turn the patient's head back to a normal position and use a very anterior posterior, approach, identifying the common carotid artery and sliding that transducer laterally, to identify this classic, vertebral artery image where you can see the vertebral, bodies here and here, and the spine here, which cast a shadow.

This is a classic image of the vertebral artery, and we primarily evaluate the vertebral arteries for flow direction.

However, when you do suspect that there's stenosis from atherosclerosis, you really want to evaluate the vessel at its origin.

However, I would recommend that you don't go immediately to the origin of the vertebral artery.

There are multiple, multiple branches that can be present here, and it can often be difficult to I, identify the vertebral artery origin itself.

What we would do, and what we recommend is that you find the vertebral artery out in its distal portion, and then you slowly work your way back, with the transducer sagittal to the long axis of the vessel, to identify the subclavian artery and vertebral artery origin.

And then use your sample volume here and doppler this area for the presence of, elevated velocities that might be consistent with hemodynamically significant disease.

Conclusion

If you'd like more information about, these protocols, I would refer you to the Society for Vascular Ultrasound's, professional Performance Guideline, DVD series, and you can get information on that@www.svunet.org.

Thank you very much for your attention.