An Introduction to Transcranial Doppler - SD

Introduction

I am Anne Jones.

I'm a registered vascular technologist, a registered nurse,
and a registered diagnostic medical sonographer.

I'm a clinical instructor of neurology at the Medical
University of South Carolina in Charleston,
and I'm here today to discuss transcranial anatomy
and transcranial doppler clinical applications.

History and Introduction to Transcranial Doppler

Transcranial doppler was introduced by Rooney Oslo in 1982
and clinically viable in 1986.

It was first utilized for the evaluation
of vasospasm following subarachnoid hemorrhage,
and it is a non-imaging pulse doppler technique,
and it is velocity driven.

Now, the velocities evaluated
with transcranial doppler are the time average mean
of the maximum, because Dr.
Oslo felt that this more accurately
reflected brain perfusion.

There was no angle correction required,
and we assumed an angle of intonation of zero to 15 degrees.

Transcranial Doppler imaging was introduced in 1990
through the use of an adapted three megahertz
cardiac transducer.

Clinical applications and technologies continue to emerge
for transcranial doppler and portability remains crucial
because of the clinical applications.

Clinical Applications of Transcranial Doppler

Who uses transcranial doppler in practice.

While primarily there are two groups,
pediatric hematologists who identify patients at risk
of stroke with sickle cell anemia,
it is considered the standard of care for these patients
between the ages of six months and 16 years,
and it assesses the impact of management
with transfusion therapy.

Neurosurgeons use ICU in the intensive care unit
to assess vasospasm following subarachnoid hemorrhage.

They monitor the rise in mean flow velocity
and implement therapy based on these changes.

The speed and severity
of vasospasm is predictive of outcome.

Other clinical applications that may not be
as widely utilized are seen here.

Now, in your own clinical practice, you may want to go
to your neurologists, surgeons, interventionalists
and hospitalists to see if there are very specific
utilizations that would work in your clinical setting.

Neurologists evaluate patients with stroke head injury,
carotid stenosis, and suspected intracranial stenosis.

They also evaluate the impact of carotid stenosis.
On intracranial flow.

Surgeons often use TCD for intraoperative monitoring
for emboli detection,
and to make sure that the MMCA is patent.

Interventionalists will monitor the middle cerebral artery
recanalization after TPA
and they will also assess stent placement.

And hospitalists use continuous intracranial monitoring in
the ICU to assess cerebral circulatory arrest.

Basic Concepts and Instrumentation

The basic concepts of TCD
are here the basic principles you use a one
to two megahertz pulse stopper.

Low frequency is necessary for inclination through the bone.

A bidirectional pulse stopper is necessary
to discriminate flow direction and sample volume depth.

And the diagnosis is based primarily on spectral waveform
using again, the time average mean of the maximum velocity.

The instrumentation for transcranial doppler really applies
to the application that you're using.

Non-imaging doppler systems have been esta the established
standard since 1986.

They're portable, they're reliable,
and the exams are repeatable,
but the learning curve is, is quite significant.

And of course, there is no image
to guide the placement of the sample volume.

Color Doppler imaging has emerging as an
as an optimal technology for monitoring intervention
because you can actually visualize and assess MCA occlusions
and other issues.

Both are still relevant,
both still have very specific utilization.

The instrumentation needs will vary
with the clinical setting and the application.

As previously mentioned, portability is very helpful
because you're often going to the operating room,
the emergency room, to the patient's bedside,
and in some cases you can travel to remote clinical sites
for sickle cell screening.

A fixed transducer is useful for monitoring so
that you can actually attach the transducer
to the patient's head using a headband
and continuously monitor.

The middle cerebral artery imaging
and color flow are optimal
for monitoring interventional procedures
or following the injection of thrombo thrombolytics.

The absence of a signal could indicate
occlusion or poor alignment.

So the non-imaging technique was difficult for these uses
and imaging is optimal.

Protocols are required for all clinical applications
and they will be discussed.

Intracranial Anatomy and Access Windows

So before attempting a transcranial doppler
or transcranial doppler imaging,
you must have a good knowledge of the intracranial anatomy.

We are assessing the arterial vascular ring at the base
of the skull known as the circle of Willis.

The circle of Willis joins the two internal carotid systems
with the vertebral basilar system.

It is the most important source
of intracranial collateral circulation
and is the primary focus of transcranial doppler.

Now, to assess the circle of Willis,
you must intonate the bone.

There are three windows
or access areas that are routinely utilized.

The temporal bone where you can intonate the middle cerebral
artery, the anterior cerebral artery,
the internal carotid artery terminal branch,
and the posterior cerebral artery.

The orbit provides visualization of the ophthalmic artery
and the carotid siphon.

So you can actually track the ophthalmic artery
through the natural opening of the eye
and, uh, track it to its origin at the area
of the internal carotid
or the S-shaped curve of the carotid siphon.

It is important if you are doing the orbital view
to lower the power settings
because you no longer have to go through the bone, the frame
and magnum is another opening, um, at the base of the skull.

And again, you can lower the power a bit, but
because you require significant depth penetration
to assess the basal artery, uh,
power levels are usually kept at about 50%.

Performing TCD: Finding Signals and Vessel Identification

The first step in doing a transcranial
doppler is finding a signal.

So you must intonate through the bone,
determine which window you will be utilizing,
and then tracking the intracranial vessels.

So you position the Doppler sample volume, um, at the,
at the uh, inter interim initially at the
middle cerebral artery.

Um, and it is really suggested
that you place the sample volume at approximately the area
that you would anticipate finding the terminal portion
of the internal carotid
where it bifurcates into the anterior cerebral artery in
the middle cerebral artery.

Because this area is rich with vascular flow,
and you can usually get a good signal in this area.

In the color flow when you place the,
the transducer at the skull,
you look at the in intracranial, uh,
reflections from the B mode image,
and if you can see the, uh, inner table
of the contralateral skull, you know
that you have an adequate signal.

You would then turn on the color so
that you could document the anatomy of the middle cerebral,
anterior cerebral, contralateral, anterior cerebral
and contralateral MCA.

And then looking posteriorly, you can get the top
of the basilar and visualize the posterior cerebral artery,
um, ipsilateral and contralateral.

So color is very helpful in this area.

You then, of course, would place the sample volume within
the vessels to document their time average meaning
the maximum flow.

So how are vessels identified with transcranial doppler?

There are several parameters, the window that you use
to insensate or the intonation window,
and that is the temporal, the orbital
or the suboccipital, the sample volume depth.

So the depth will help us determine, uh, the level
where the flow is being evaluated
and the flow direction is very helpful in
vessel identification.

The probe angle is also useful
because as you can see, you can angle completely straight on
at the anterior circulation,
and if you angle posterior laterally
and a little inferiorly,
you can pick up the posterior cerebral
arteries in the top of the basilar.

Now, the traceability of vessels is very important.

The middle cerebral artery is the longest
and straightest vessel, so it is the most traceable.

But the audio signal gives you very helpful information
and can help you optimize the waveform just
by using your ears to know
that you have the sample volume placed
within the middle of the vessel.

The spectral waveform
and velocity appearance are very important,
and this is where we focus most of our energy.

As you look at this spectral waveform display,
it may not look optimal to you,
but there are very important pieces
of information displayed here.

First of all, we see that the flow that is displayed
above the baseline is moving towards the transducer,
and usually your systems will demonstrate some form
of letting you know where you have forward and reverse flow.

Obviously, with the color flow,
you can demonstrate that with the color bar.

In addition, you'll see
that the scale setting is quite high,
and when you anticipate that you're going to find disease,
particularly in vaso spasm or
or sickle cell anemia, it's good
to have the color bar maximized
and to lower your baseline so
that you can fully display the entire waveform
and, uh, not cut off the peak so
that you're not acquiring the best information.

It is also important to have the color follower
tracking the outline of the waveform very carefully so
that it is picking up flow information
and it's not picking up background noise.

Now, you can see in this image
that there is some background noise, and we do this
because a little bit of background noise indicates
that you have got the proper gain setting to be sure
that you have acquired all of the useful signals
and information for calculating the time
average mean of the maximum.

Waveform Optimization

So optimization of the waveform not only means positioning
the sample volume within the vessel
to get the strongest signal,
but also displaying it so that you can, uh,
calculate an accurate mean.

The spectral waveform is crucial,
and we do focus on this significantly
because it is the basis for determining whether a, a,
a study is normal or abnormal.

So you optimize the signal
with the best sample volume placement,
and you can see that if your,
that your sample volume is actually larger than the vessel.

In most cases, we generally use a six
to eight millimeter sample volume in vessels
that are sometimes as small as two to four millimeters.

So the sample volume completely in cases the vessel,
if you have it placed properly,
this ends up showing you a spectral display
that is completely filled or somewhat broadened
because you are sampling across the entire vessel.

The envelope follower is very critical,
and if the envelope follower is picking up a lot
of random signals in the background,
then you will not end up
with an accurate mean flow calculation.

The best quality spectral display
with the minimum back background noise is optimal
and the scale must display the entire spectrum.

Why emphasize tam?

Well, the clinical management is determined by the numbers,
so failure to optimize at every step may result in
misidentification of vessels
or failure to identify the highest velocity.

So once you find a signal that is abnormal, you need
to spend a great deal of time optimizing the signal
and making sure that you have captured several wave forms so
that you can use the, the highest velocity
and the strongest signal to make your decision.

Now, it's not just all about peaks
and means it's about the quality of the signal as well,
because when you get into, um, high flow states
and distal to high flow states,
you have the same characteristics
as you do in other vessels.

You have a damping of the waveform, you have turbulent flow,
and all this information is very helpful.

Now this is a typical, um, TCD waveform
and this is the kind of thing we like to see.

You can see that that the gain setting is high enough
to completely fill in the spectral display.

The envelope follower is carefully following the entire
outline of the vessel, and there is a little bit
of background noise indicating
that you have set the proper gains
to optimize your signal color.

Doppler adds assurance to spectral acquisition
and it maps the anatomy.

And this certainly to new users is very helpful
because you can visualize the information you are trying
to see to evaluate
and then place the doppler sample volume at
discrete points along the vessel.

Now, it is important not
to just drop the sample volume at one or two places,
but to clearly track across the whole vessel
because very small movements in these small vessels can
cause you to miss something that could be important again,
uh, making your diagnosis based on a beautiful spect
spectral waveform display.

Protocols and Technique

Protocols are fun fundamental in most, uh,
imaging procedures,
but very critical in TCD, especially in pediatric patients,
because they have small heads, small vessels,
and very small changes in the angle
of the transducer can actually cause you
to pick up a different vessel.

So protocols provide consistency, they provide repeatability
and reliability, and when we're doing serial evaluations
and we're monitoring the impact of therapy,
repeatability is crucial.

So a standardized technique means that you have a,
you can acquire objective data, objective numbers
and make decisions.

You can come to a well-defined endpoint
and the management then is based on objective numbers.

Protocols and technique are specific to the type
of exam that you're performing.

So even though there are certain fundamentals
that are always acquired when you're doing A TCD,
you may adjust your protocol
and your technique based on
what the clinical question that's being asked.

What are the presenting symptoms of the patient?

Do other vascular studies provide information?

It is helpful to be able
to look at an extra cranial carotid study or a CT
or an MR or an angiogram.

Um, this isn't cheating, this is helping acquire all
of the data to make the right diagnosis.

Is the study part of an interventional procedure?

If it is, you may decide you want to use imaging
as opposed to non-imaging.

Can you acquire a baseline exam for reference?

This is really important when you're doing, uh,
daily monitoring.

When you initially start a on a patient, it's very helpful
to be able to do a bilateral exam
and then determine if you need
to do a complete exam in the future.

Is the study gonna be bedside in the
or ICU er or vascular lab?

This may determine which, which machine you use.

And also it's also helpful to use the same machine
for follow-up exams so that you're sure
that you are measuring the, the data the same way each time.

Is the examiner experienced or are they new?

We found that using transcranial imaging is very helpful
for new folks because it helps them visualize the anatomy
and get comfortable with the, um, evaluation.

Expected Depths and Velocities in Adults

Now, in performing transcranial doppler in adults,
we do have expected depths
and time average mean to the maximum velocities,
and as you can see, there is a bit of a hierarchy of flow.

The middle cerebral artery, again, as I mentioned,
is the longest straightest vessel carries about 80%
of the flow, and so we would expect it
to have the highest mean velocity.

The average depth from the
but from the side of the skull is 30 to 65 uh, millimeters.

So in this area you have a long traceable course.

The anterior cerebral artery carries the next highest
velocity of, uh, volume of flow velocity, and that's 50.

And then as you go down, the reason I point this out is
that if you see an, an alteration in this hierarchy scheme
and you see that the internal carotid
or the posterior cerebral artery have a higher mean flow
velocity than the middle cerebral, then
that would make you think I need to look more carefully,
have I intonated the wrong vessel,
or is the posterior cerebral artery carrying a great deal
of collateral flow and is something going on in
the middle cerebral artery?

So these baseline expected depths
and numbers are useful in helping you evaluate both normal
and abnormal patients.

Factors Impacting Collateral Flow

Now, factors impacting collateral flow also
need to be remembered.

If you have a proximal
or distal stenosis, you're going to have the same type
of waveform changes that you have seen in other vessels.

If there's arterial narrowing in such
as invasive spasm in sto stenosis
or in focal diameter reductions such as sickle cell anemia,
you will have the same increased velocity.

If you have an arterial na narrowing such
as vasospasm stenosis
or focal diameter reduction such as sickle cell anemia,
you will have a predictable increase in in mean flow
velocity at the area of narrowing,
and then you'll have a predictable waveform
changes distal to that.

If there is occlusion, you wanna make sure
that you have intonated both sides of the patient's head,
try to demonstrate flow in the other vessels to make sure
that you have got a good window
and it's not just a technical problem
and you may decide that you want to, um,
to use a different type of equipment to evaluate that, such
as an imager changes in CO2.

Um, we have seen in evaluating patients, the children
who were doing sickle cell anemia studies, that if they go
to sleep and their CO2 increases
that they can actually increase their mean flow velocity.

Now you may say, well, it's good to have a sleeping child.

Well, it's not when you're trying to use the numbers
to objectively decide which category
of disease these children will be placed in,
which will impact their management.

So if they go to sleep
and they make their CO2 go up, they will actually,
you'll actually see a rise in the mean flow velocity.

As we know, flow velocity decreases with age.

So the normal values
that you would see in an 80-year-old would not be the same
as the normal values you would see in a
40-year-old and in head injury.

There are other factors that will impact
the intracranial flow.

Common Clinical Applications of TCD

So what are some of the common clinical applications of TCD?

And there are many applications I'm going
to focus on the ones that you will probably most routinely
encounter in your clinical setting.

Vasospasm Following Subarachnoid Hemorrhage

Ruptured intracranial aneurysm
and vasospasm following hemorrhage was the first
and is still one of the standard uses of TCD.

It was the first clinical application, and it is
because annually in the United States,
we see over 30,000 ruptured intracranial aneurysms.

Half of those patients die within minutes.

And for those that do get to the hospital, um,
it is very important to be able to, uh,
treat them and monitor them.

The location of the aneurysm, uh, uh,
of the vasospasm is based on the exposure of the arteries
to the blood leakage in the brain,
and they most commonly occur in the, um,
anterior cerebral artery, the internal carotid
and the middle cerebral.

Although we do see from this slide that we do have, um,
aneurysms in the posterior circulation
and the basilar artery, the hemodynamics of vasospasm,
what's happening is that the body is attempting
to maintain flow volume and
therefore they have to increase the flow velocity
to deliver the blood flow to the brain.

The elevated velocity often precedes the onset
of neurologic symptoms, and this is very helpful
because then the, the management
of the patient can be changed so that the medications,
the volume of, of fluids
that they're getting will help maintain perfusion.

The velocity data directly impacts the management decisions
and, uh, the, a study is usually required every 24
hours in these patients.

And abrupt increase in flow velocity from one day
to the other indicates a poor outcome.

And you can see that normally when we do TCDs,
we will actually track the mean,
the highest mean flow velocity that we acquire,
and we will do it on either a chart, a flow chart,
something like a temperature chart in the patient's, uh,
chart so that the physicians can see the changes over time.

The vasospasm protocols and criteria are pretty specific.

Um, the, the maximum velocity is usually reached at about
seven to 12 days.

It tends to resolve over three weeks,
although I have actually seen patients at six week follow
ups and they still had elevated velocities.

Mild vasospasm is considered at 100
to 120 centimeters per second.

Moderate is greater than one 20 to 200
and severe is greater than 200 centimeters per second.

And here there is a risk for ischemia.

A rapid increase or greater than 25 centimeters per second
rise per day is indicative of a poor outcome.

Now the exam protocol is fairly specific.

You'll initially perform a complete baseline study the right
and the left, identify the highest velocities,
and then when you do your monitoring daily,
you may just be able to perform a unilateral study,
whatever is indicated in that partic
particular patient setting.

Now, many of these patients have had their aneurysm clipped,
so they'll have a surgical site
and you will need to use sterile technique.

It's helpful to notify the nursing
staff when you will be coming.

So if there's going to be a dressing change,
it can be done after your study.

And the TCD or the TCDI, you can use, um, either one,
but just make sure that you use the same equipment
for follow-up exams.

Sickle Cell Anemia in Pediatrics

In the evaluation of pediatric patients
with sickle cell anemia,
transcranial doppler has made a significant difference not
only in their evaluation but in their management.

Now, there are focal TCD velocities
because sickle cell anemia creates changes in the arterial
anatomy with focal areas of narrowing,
which impacts flow in a manner similar to
what we see in atherosclerotic narrowing.

There's potential for thrombotic
or ischemic events in these patients.

Patients with sickle cell anemia have distorted red blood
cells and chronic hemolytic anemia.

So when you think of anemia, you think
of viscosity and you think of flow.

So normally in these patients,
they will actually have a higher normal mean flow velocity
than you see in other, uh,
patients without sickle cell anemia.

Cerebral infarction associated with occlusive vasculopathy,
vasculopathy of the distal internal carotid artery
and the middle cerebral artery is common.

Stroke prevention is possible
through chronic transfusion therapy,
and now other, um, drugs are being evaluated as well.

So what we will do is monitor the intracranial velocities
with transcranial doppler, uh,
as a screening tool when they're being treated and, um,
and until they reach the age of about 16.

Now, one of the initial landmark studies for, uh,
evaluating children with sickle cell anemia was the stroke
prevention trial and sickle cell anemia or the stop trial.

The stop trial enrolled 130 children between the ages
of two and 16 years.

They were at a high risk
of stroke if the mean velocity in the middle cerebral
or the distal internal was greater than 200 centimeter
centimeters per second on two, uh, positive exams.

So we would perform one exam
and then repeat it within about a two weeks segment.

Randomization for transfusion therapy
or standard care occurred after one year.

10 children in the standard care group had had,
had a cerebral infarction
and only one child who was receiving transfusion therapy.

A clinical alert from the NIH recommended
that transfusion therapy, uh, to maintain hemoglobin s
below 30%.

Now, the pediatric exams have very specific issues.

The children are young, they, um,
and young children have the highest velocities.

Normally, they are usually anemic.

The low hematocrit
and viscosity, um, means that you have
to have two times the volume of flow
to deliver the same level of oxygen.

So minor and also minor changes in CO2,
as I previously mentioned, will impact the velocity as well
as the wave form shape.

So you have to make sure your children aren't falling asleep
and the velocities are drifting higher.

They need to be in a steady state, meaning
that they don't need to be in the midst of a sickle crisis.

They need to have no fever.

Um, and although it is tempting
to perform studies on these children when they're in the
hospital because you can have a, you can get access to them,
it is better to do them at a steady state.

Um, in addition, it is important to remember
that performing a study on a child with sickle cell anemia,
uh, means that you are looking at a very small head
and the vessels are small and, um,
and not separated greatly from the
anterior to the posterior.

So it's important to know in order to predict the level
of the bifurcation
and the depth of the vessels, we find it's helpful
to do a bitemporal head diameter.

And we actually get these from the, from folks
that do eye exams,
and we actually measure right in front of the, um,
right in front of the ear and do a bitemporal measurement.

And what this tells us is that we know then
where the midline is
because we divide the bitemporal diameter by two.

And we also know that the, uh,
intracranial bifurcation is usually about
10 millimeters from the midline.

And this is very helpful when we're doing the exam.

Now the examiner for doing the TCD is usually sitting at the
head of the bed with access
to the instrument in the patient.

And the reason we do this is that these can be long exams,
so it's good to be comfortable
and have your arms resting at the head of the bed.

It's also to have good access to your little patient's head,
make sure that they're not moving
and that you can see them completely throughout the exam.

You need to be co comfortable and in a quiet room.

And although a quiet room often makes the children go
to sleep, sometimes we'll actually do videos so
that it'll keep them focused, explain the procedure
to the patient, measure the head diameter,
and record the head diameter, keep the child awake.

The sample volume size
that we routinely used in the stop trial was six
millimeters, and we would initially set the scale
to display peak velocities of 250 centimeters per second so
that we could display the entire waveform
and get a good, uh, mean velocity calculation.

We would usually begin the exam at a depth of about 50
because that's where we anticipate the bifurcation
and we have a high probability
of getting a good quality signal at that depth search
until the strongest signal is found.

Save the, and then, uh, step the sample volume out
and track through the entire course of the vessel.

So we'll usually begin the study at about 36 millimeters
and track until we get to the midline.

Save the waveforms at two to four millimeter increments so
that you make sure you are staying in the vessel,
you're tracking the vessel
and not moving out of that vessel.

All exams are bilateral
and the highest vessels are recorded in all the highest
velocities are recorded in all vessels.

And this is just an example of how we would track
and save all of the intracranial velocities.

You can see any changes and then you can go back
and recapture signals that you may think are not optimal.

Now the sites of intracranial narrowing in pediatric sickle
cell are the distal internal carotid and the proximal MCA.

So the numbers that we use for, um,
for categorization apply only to these vessels.

So TCD exam for sickle cell, they're small arteries.

We're, we're evaluating what I call moving targets
or squirmy little children.

So you have to stick to a very strict protocol.

You must avoid false positives and false negatives
because it will either mean that they withhold treatment
or they provide treatment unnecessarily,
and the results actually change the management.

So you wanna rac the entire course.

As previously mentioned, you also wanna do evaluations,
the posterior cerebral artery
and the top of the basler, again, noting the the midline.

You will do two measurements from the posterior, um, uh,
eva, uh, from the posterior, uh, evaluation
through the frame and magnum.

And we do not routinely use ophthalmic evaluations in sickle
cell protocols because we found
that the children really did not like the transducer
being placed over the eye.

We also found that it did not provide a significant
additional information.

Acute Stroke Intervention

Other clinical applications of transcranial doppler.

I'm going to just step, uh, to just, uh,
touch on very briefly acute stroke intervention
and TCD monitoring of the MCA.

Um, we know that, uh,
TPA must be administered within three hours.

It is a very short window,
so you will probably be called emergently
to the emergency room or the, um, stroke ICU you.

It's helpful if you can do a bilateral TCD initially just
to document that you have good temporal window windows
that you have, uh, a flow
that you can document the flow pattern
and the direction of the circle of Willis vessels.

Um, the reason that we try to do both sides is
that you do wanna document that you have a good window
and that you're not seeing an absence of flow just
because it's a technical issue.

Position the sample volume in the area
of the middle cerebral artery during, uh, the, uh,
administration of the, uh, the TPA
and monitor at that same depth throughout the evaluation.

Recanalization is indicative of early recovery.

Persistent arterial occlusion, as you can see,
bears a poor prognosis.

This is one area where the, um,
imaging is really very helpful.

You will probably want to, um, set your frame rate
and your, um, your, uh, gain so
that you can optimize the quality of the signal and, um,
and make sure that you do not Ms. Small changes in the flow,
um, as you're trying to monitor.

Again, of course, it's very helpful
to have the waveform information
and monitor the change in the mean
flow velocities over time.

Emboli Detection

TCD monitoring, uh, one of the key uses is
for emboli detection.

And, um, a lot has been written about this in the literature
and really it boils down to the fact
that you must have four key figures.

Um, the, um, signal must be transient and brief
and less than 300 microseconds.

The signal amplitude is greater than three decibel higher
than the background.

It must be a unit directorial doppler signal,
and it must be accompanied by an audio characteristic,
which is, uh, often a, a snap, a chirp or a moan.

And it is most frequently seen in patients
with carotid stenosis
who may be embolizing prosthetic cardiac valves or pfos.

And this is the type of signal
that you would see with emboli.

Now this is quite massive
and um, it is really almost a chaotic type of signal
that you see with all of these emboli flooding
through the area of the middle cerebral artery.

Often there's aliasing of course,
or you may have a variety of high intensity signals
where you just get an occasional chirp
or, um, in, uh, the, the high intensity, um, or the hit.

Um, in the wave form you can see
that you have the middle cerebral artery wave form being
displayed here, and then the hi is quite prominent Now

Intracranial Stenosis

for intracranial stenosis, if this is the only reason
that you're doing TCD, you're gonna be disappointed
'cause you will not see it all that often.

But, um, again, it is one of the areas
where we have an absolute velocity
criteria is not reliable due to variables of age,
hematocrit and vessel size.

However, generally the mean
of 80 centimeters per second in the middle cerebral artery,
A-C-A-P-C-A or distal internal are cause for concern
and would probably warrant, uh, uh, other, um, assessments
with other procedures greater than a
hundred centimeters per second.

In the middle. Cerebral artery is highly predictive of, uh,
greater than 50% stenosis.

Stenosis is most likely to occur at the siphon.

That s-shaped curve of the internal carotid artery,
the distal internal carotid
where it bifurcates in the middle cerebral artery,
a focal increase of 25%, um, is suspicious of stenosis
as compared to the proximal and distal areas
and the contralateral side.

Now this again, is a waveform we've seen before,
but it demonstrates what we would expect
to see in a stenosis, um, baseline, uh,
high amplitude signals a weaker high, um, the high,
high velocity signals, um,
and an overall, um, increase in velocity, a mean
of 176 centimeters per second.

Impact of Extracranial Disease

Now, when you have extra cranial disease, uh,
many neurologists like to use the TCD to evaluate
what they call the impact of of carotid stenosis.

If you have a hemodynamically significant lesion in the
neck, you wanna see if it's actually impacting flow
intracranial, if there are adequate collaterals
and if the patient is compensating.

So once you've seen something like this, you would then go
and do the intracranial assessment,
and frequently we will see something like this
where we have a demonstrable, uh,
change in mean flow velocity from the ipsilateral
of the affected side and the contralateral side.

You would then look for the source
of collaterals using your, um, your entire TCD study
to see the, uh, flow directions
to see any changes in the hierarchy.

In this case, you can see
that probably the anterior cerebral artery would be higher
than the middle cerebral artery on the affected side.

In addition, you might expect to see a flow reversal so
that you have a cross filling from the right to the left.

Um, in these patients,
you also frequently see increased flow in the
posterior cerebral artery.

Summary of TCD Applications

So in summary, the TCD impacts patient management,
invasive spasm, sickle cell anemia, monitoring
and intervention, um, evolving applications,
complement extracranial studies.

The non-imaging TCD has clear applications
with standardized technical and interpretation protocols
and imaging techniques are very effective
in most applications.

Performing TCD Protocol Exam for Sickle Cell Anemia Patients

Now I'm going to actually move into a quick, um, summary of
how to perform A TCD protocol exam
for sickle cell anemia patients.

This protocol can actually be adapted to other procedures,
but it is very specific for just the children.

With pediatric, uh, pediatric patients
with sickle cell anemia, again, the the head diameter needs
to be measured before you do the study.

That helps in, in helping you figure out the vessel depths
and it aids in in vessel identification.

There are many bi-directional signals in, um, intracranial.

So this helps identify the depth of the midline
and, um, helps the interpreter of the study as well
as the examiner, um, decide which,
which bifurcation means what.

And I'll show you examples as we move forward.

The ICCA bifurcation is generally 10
millimeters from the midline.

So it's a good reference point when you get lost when you're
doing the study, you always go back to the bifurcation
to help you get grounded, figure out where you are
and continue to move forward.

In the pediatric TCD protocol, we record all wave forms.

We figure it is better to have more information than,
than less information.

And uh, frequently if you see a signal and the,
and the child becomes uncooperative,
you may not get it again.

So it's always important to, to save every signal.

Now we will initially begin by looking at the area
of the anticipated bifurcation
where you would usually have your strongest signal.

It'll help you optimize what is your best temporal window,
and then track the, the sample volume depth out so
that you're sure that you have traced the course
of the middle cerebral artery,
that you haven't gotten confused and,
and you're tracing the posterior cerebral artery
and it's carrying collateral flow.

So the reason that we do all of these vessels is
to differentiate that you've been in the anterior
circulation as opposed to the posterior,
and that you have clearly tracked the most suspicious
vessel, which would be the middle cerebral
and the termination of the internal carotid.

So you begin at 50 at the bifurcation, step out,
and then begin to track from about a depth of about 38
to 50 millimeters following the entire course
of the middle cerebral artery, the bifurcation,
you'll have a bidirectional wave form, um,
demonstrating the middle and the anterior cerebral.

The anterior cerebral artery will have flow towards the
midline, so it'll have flow as way from the transducer
and the distal internal carotid.

Because of its position
and its angle, it is suboptimal for doppler evaluation
and you'll have to actually angle inferiorly to be able
to get that distal internal carotid.

And so you will end up with a blunted waveform.

It is important to do
however, just to demonstrate that it is patent
that you have, uh, the normal flow direction.

And if you are evaluating the distal internal carotid artery
and you find that you have a great deal of turbulent flow
or disturbed flow, it may indicate
that there is a more proximal lesion in the siphon.

And at that point, you would want
to take a look at the orbit through the orbit,
the posterior cerebral artery.

When you are doing these studies, you'll see
that these are really very close together.

It only takes a tiny movement to move from anterior
to posterior, and you want to make sure
that you intonate the P one segment
of the PCA from its origin at the top of the basler
to the posterior communicating artery.

And then at the P two segment, it tends
to wrap around the brain stem.

So we can't really follow that too far.

So once a strong signal is, is isolated
and optimize, you decrease the depth of the sample volume
to about 38 to 36 to 38,
and then you begin capturing signals.

Now in the stop protocol,
we actually recorded this 38 millimeter depth as M1.

This is not anatomically, um, where we are in, if you,
if you compare it to Grey's Anatomy,
but we meant at as the first M-N-M-C-A signal
that is being captured, then you will increase the depth
by two millimeter increments, record
and optimize the waveform along the entire course from the
middle cerebral artery to the bifurcation.

And you step through the entire MCA.

You can see we've gone 42, 44, 46, and 48.

And when you look at, um,
the differences in the mean flow velocity from the terminal
MCA to the main trunk, you can see
that the flow velocities increase.

You can also use the, um, imaging to do the same thing.

You would visualize the vessel
and step the sample volume across the entire, uh, anterior
and posterior circulations.

So as you continue the middle cerebral artery protocol,
you can see that we continue
to follow the middle cerebral artery.

We get to the point where the internal carotid has
bifurcated into the A CA and the MCA.

And because the sample volume is evaluating this area,
you will get a signal that looks bi-directional.

This is the most reliable intracranial landmark used
to identify all other vessels.

It has a strong forward flow in the MCAA strong
and a reverse flow in the a CA
and the depth must correlate with the head size.

So this is again, why we measure the head diameter
so we know where to anticipate the um, bifurcation.

Now, as I mentioned earlier, the internal carotid artery,
again, we're still using the temporal approach
and we can see that in order to intonate into this area
of the ICA, we will have to angle inferiorly
and it will be a suboptimal signal.

It'll be a bit of a blunt or damped wave form,
and you can actually hear the gruffness of the, um,
of the signal when you're doing the,
your velocity evaluation.

So it's a harsh, blunt audio frequency, um,
but it is still valuable.

It provides valuable information.

So this would be the internal carotid artery.

You can see that it is a lower mean velocity than we saw in
the middle cerebral artery.

You then increase the depth of the sample volume, uh,
track it four millimeters from the bifurcation
and record an anterior cerebral artery.

And because the acas are anatomically challenging
and may go off at great angles,
you can usually only routinely follow at about a depth
of four to six millimeters, document the flow velocity
and the mean flow and the, and the direction.

Comparing the middle cerebral artery
to the internal carotid artery, you can see
that there is a significant difference in the mean flow
velocity and the volume of each of these vessels.

Now to evaluate the posterior circulation,
you are still in the temporal approach
and you angle slightly to the posterior.

Um, I usually just increase the depth of the sample volume
to where I would expect to find the midline,
and that way you will get the top of the basler.

At that point, you, you have gone from the bifurcation
landmark to the middle of the head
and looking at the top of the basler landmark.

And here because both PCAs are originating from the top
of the basler, you're going
to get another bidirectional signal.

It is also important to keep in mind that the um,
mean flow velocity of the PCA is less than the MCA,
but it does still have continuous diastolic flow.

The superior cerebellar artery runs artery
runs parallel to the PCA.

So you have to make sure that you
differentiate between the two.

The, uh, superior cerebellar artery has a more pulsatile
characteristic, um,
and you can differentiate from the PCA
that way the flow velocity may increase in the presence
of intracranial stenosis
and you wanna track it towards the midline.

Now this would be a typical posterior cerebral artery in a
child with sickle cell anemia.

You can see our depth is 60
and this is about midline In the normal head,
they're usually, their head diameters are about 120 to 125.

So this is approaching the midline.

So you can see you've got the ipsilateral PCA
and you're picking up a little of the contralateral.

Because of the size of the sample volume, you can see
that the mean velocity is much lower than we saw in the
anterior circulation at about 97.

Now, tracking the PCA to the midline is helpful
in the umto stop protocol
because again, we wanted to make sure
that we didn't misdiagnose the middle cerebral,
the posterior cerebral artery as the middle cerebral artery
because the overall characteristics of continuous flow
during diastole are there.

But you can see that the mean is much lower.

The overall, um, uh, display
of the waveform is a much lower signal.

And of course, the depth of the bifurcation
or the bidirectional signal is deeper than you would expect
to see at the area of the bifurcation.

One last part of the study is
that we look at the basilar artery for comparative purposes.

Again, we wanna see if this is a, um, source of collateral,
um, and we wanna make sure
that there's no intracranial disease here.

It is pretty rare. So we actually turn the child on their
side and tip their chin to the chest
that we can open up the, the back of the head
and get access through the frame.

And magnum. We apply the gel to the transducer
and angle the probe
as if you're shining a light between the eyes.

We, we actually set the default depth to 74 millimeters so
that we are actually ignoring the vertebral arteries
and intonating, uh, just the, um, the, uh, basal artery.

Now we can see that, um, we're at a depth of 64
and this, this would be, um, the area just
as we're picking up the two vertebral arteries as we move,
um, to the basilar artery.

But we don't normally record the vertebrals
for the sickle cell study.

Now this is a beautiful example of an image, um,
of the vertebral basilar system.

You can see the opening of the frame in Magnum,
the two vertebral arteries, some of the branches.

And then positioning the sample volume in the basilar artery
flow is away from the transducer
and nicely displayed with the,
with the envelope follow are clearly defining the,
um, the mean velocity.

Interpretation of TCD for Sickle Cell Anemia

So the interpretation of TCD with sickle cell anemia,
we want to have the highest recorded velocity in each
intracranial artery.

Um, we know that these children usually have a hematocrit of
between 19 and 27%.

Um, and um, this again impacts their, their velocities
and a mean flow velocity
of greater than 140 centimeter per second indicates
increased cerebral flow without focal stenosis.

So the interpretation of the TCD
for the clinical trials mean flow velocity in the MCA
or the ICA less than one 70 is classified as normal

mean flow velocity greater than
or equal to one 70, um, is considered conditional

and mean flow velocity greater than
or equal to hundred was considered abnormal.

All abnormal findings had
to be documented on two separate occasions.

So it's important to never compromise in these studies
because it really does impact the patient's future.

So TCD is a standard of care for patients
with sickle cell anemia.

You begin studies at six months
and continue through 16 years.

You compare the studies to previous exams.

So it's always helpful to have a baseline study.

Increased velocity in the distal internal
and the MCA are significant changes in the a CA should be
monitored because we have seen that some of these patients
that have high velocities in the A CA then ultimately change
over in the ICA or the MCA as well.

Conditional exams need to be repeated every six to 12 months
and abnormal exams on two consecutive, um, if, uh, times if
indicate the need for treatment.

Conclusion

Thank you for your attention.

You can reach me at this email, um,
if you have any specific questions.