Transcranial Doppler - SD

Introduction

Hello, my name is Annemarie Kapinsky.
I am the president of North Country Vascular Diagnostics
and also a clinical associate professor
of radiology at Albany Medical College in Albany, New York.
And today I'm going to be speaking on transcranial doppler.

Anatomy of the Circle of Willis and Related Vessels

To begin this discussion of transcranial doppler,
we'll start with anatomy,
and that's important, obviously
to understand what we're looking at.
Certainly. We all know about the circle of Willis, and,
and that was named after indeed,
sir Thomas Willis,
who'd first described it back in the mid 16 hundreds.
And the circle of Willis is comprised of five components,
and you can see them listed here.
The terminal portion of the internal carotid artery comes up
and actually,
branches.
One of the branches it,
feeds into is the anterior cerebral artery, which extends
and communicates with the anterior communicating artery,
forming the anterior part of the circle of Willis.
Along the posterior aspect is the posterior communicating
artery and the posterior cerebral arteries.
And this diagram better shows the
orientation of these vessels.
We can see here is the terminal portion
of the internal carotid artery coming up.
And we know the large branch here is the middle cerebral,
but that's not really part of the circle of Willis.
The circle of Willis here is comprised
of the anterior cerebral
and again, anterior communicating as well
as the posterior communicating leading back
to the posterior cerebral.
And we'll talk more in detail about all these vessels.
The internal carotid artery or ICA comes up
and when it enters the cerebral portion,
it branches into two main branches,
the anterior cerebral and the middle cerebral.
The middle cerebral, of course, is the largest,
and it the ICA also gives, gives rises
to several small vessels.
An important one, of course, is the ophthalmic artery.
The ophthalmic artery is shown here in this
diagram from Grey's Anatomy.
You can see over here the distal portion
of the ICA coming up.
And this is the first branch
of the cerebral segment of the ICA.
It comes up coming into the back of the eye
and gives rise to several small branches.
The important part here is the flow direction would be
coming from the ICA into the eye.
So if we were intonating through the orbit of the eye,
which we do during transcranial doppler, we would see
that flow coming towards us.
Another important aspect of the ophthalmic artery is
that these small branches here,
can,
collateralize with distal branches of the ECA, namely,
the superficial temporal and the facial.
Now, the middle cerebral artery really has a big job to do.
It supplies all the circulation, really most
of the circulation to the lateral aspect
of the cerebral hemisphere.
There are several segments,
of the middle cerebral artery.
They're really not important.
They're designated actually though, as the branches form.
For this discussion, we'll just call the,
and talk about the middle cerebral as
one vessel.
Even though obviously there are many branches,
it is really the most common site of trouble for us in
that it can,
often have the stenosis occur at the middle cerebral as well
as an occlusion from an embolic event.
And it also can get aneurysmal disease.
Now there are many anatomic variants
with the circle of Willis.
Hopefully,
most patients have an intact circle
of Willis, but sometimes the
anterior communicating is absent.
Sometimes the posterior communicating is absent
or hypoplastic, and either posterior
or anterior cerebral vessels can be absent or hyperplastic.
When those,
events occur,
other vessels may dilate in response to missing segments.
And it's obvious that if there was,
an embolic event
and circulation was cut off to one branch,
that collateralization around the circle from the other side
of the
brain is important
to obviously maintain perfusion and prevent a stroke.

Transcranial Doppler Equipment and Windows

Now, when we talk about transcranial doppler,
let's talk about the equipment for a second.
We need a low frequency transducer so we can get good,
sound penetration
and not run into too much trouble with attenuation
'cause we are fairly deep
and we need that power to transmit through the bone.
There are certain windows in the cranium that allow us
to penetrate and get some information.
And transcranial doppler really is all about,
looking at velocity and direction of flow.
Now, clinically there are multiple applications
for transcranial doppler, looking
for intracranial vascular disease,
vasospasm monitoring children with sickle cell,
looking at collateral pathways, detecting emboli,
various monitoring during procedures.
And we can also use,
TCD to look for patent
for amino valley, which I'll talk about in a little bit.
And also to aid in the confirmation of brain death.
As I mentioned before, there are several windows
through the, through the skull that allow us to see in
and intonate these vessels.
And this diagram is,
borrowed from a book chapter
by Myra Katz, who's pretty experienced in
transcranial doppler.
And there are really four main windows.
The transtemporal window here is illustrated,
by letter A, the transorbital through the eye,
through the frame in magnum as shown in C
and the submandibular approach,
and depending on what view we're looking at,
is you'll see the different vessels
as we come in from the side.
We're gonna be really close to the MCA
and the a CA if we come in posterior through the frame.
And magnum, of course,
we're gonna be seeing the vertebrals in the basler here
from the transtemporal window.
As I said, looking at the diagram here, the bone right in
through here is thin enough.
And as we come through the bone, we actually do see part
of this,
brain here.
And,
there are landmarks that we use to localize,
but some folks have temporal bones, which are just
too thick, too dense to allow the,
ultrasound
to be transmitted through adequately.
And this is actually can,
can be found in up
to 25% of the population.
So again, from this window, what are we gonna look at?
We're gonna look at the middle cerebral as well
as we can see the anterior communicating
or anterior cerebral, sorry.
And,
posterior cerebral
and posterior communicating from the
posterior aspect here through the frame.
And magnum, the sub occipital window, sorry,
we use the frame and magnum and we can see the right
and left vertebral as well as the basler.
But from this approach,
those vessels are actually coming in, going in,
bringing blood to the posterior part of the brain.
So we normally see the flow direction away from
us through the eye.
When we look, we see,
the ophthalmic artery.
We can also visualize the carotid siphon,
but we must be careful here and reduce our power output.
That's essential,
so
that we don't cause any potential damage to the retina.
Here's a view here. We can see the
globe of the eye right here.
And we can see these are probably,
ciliary arteries along the back of the eye.
And way back down here is the ophthalmic artery.
And again, that's going to be coming off the ICA,
which is out of the picture deeper here, coming up
and giving branches
or giving rise to all the branches that support the eye.
So normally flow direction is towards us.
We can see that it's color coded red.
It's a positive doppler shift.
This is a normal flow orientation in the ophthalmic artery.
And again, transcranial doppler is one of those areas
where we really have to pay attention to our power output
and remember bio effects that can
and do occur with ultrasound.
And we need to just do this as quickly as possible.
Put our power levels as low as possible.
And remember the rule of elara as low
as reasonably achievable.

Techniques for Transcranial Doppler

There are two primary techniques for transcranial doppler.
There's the blind doppler technique
or transcranial imaging,
which utilizes ultrasound,
images.
The blind TCD technique can be accompanied by M mode,
as found on many of the newer,
pieces
of equipment in general.
Most of the time we look at mean velocities with the intra
cerebral or intracranial vessels,
and we need to know what sampling depth we're looking at.
If we're using duplex ultrasound
and we're doing imaging as well,
we always leave the angle correction set to zero.
And that's by standard convention.
Sample volumes are usually wider than the vessel.
That's obviously, so we can find these small vessels
and achieve good sensitivity without reducing,
or with,
keeping the signal to noise ratio at a minimum
and reducing the,
background noise.
But because the sample volume is large,
we'll get spectral broadening that will occur
and we may get more than one artery displayed.
We use mean velocity as I mentioned, over peak
because mean velocity is less affected
by heart rate contractility,
peripheral resistance,
and it correlates better
with the overall perfusion to the brain.
Here we have an image,
coming from
a trans temporal approach as we can see here.
And in order to figure out what vessels we're looking at,
we need to know what window we're looking at.
So if you have a standard protocol that needs
to be documented
or if you are evaluating,
some,
information should be displayed
for the interpreting physicians
and we'll go by the depth of the vessel,
what direction the flow is,
appearing on color, if we can tra
trace back
or track back that vessel.
And we're going to use that all with both modalities
as well as the image when we are using,
transcranial imaging.
Here again, is just showing,
an approach
through the temporal window where we're gonna see our MCA.
And here's the duplex image showing the same thing
with our pretty wide sample volume size.
But we're seeing this nice middle cerebral artery
tracking down a little bit deeper through the same window.
We now see we're just coming up to
where the anterior cerebral comes off.
And now the flow directions changed
because that vessel is bringing flow towards the center
towards the midline.
The colors changed to indicate a negative doppler shift
as well as the spectrum going
and pivoting back slightly.
As you can see from this view, we're still transtemporal,
but now we've just angled back
'cause we wanna try to catch that posterior circuit
and we can see the posterior cerebral
artery coming towards us.
You almost never appreciate the posterior communicating
vessel, which would obviously lie somewhere in
between these two segments coming up through the frame.
And magnum, again, we see the basler artery fairly deep.
It's going to be the deepest vessel,
that we're going
to be looking at here.
And we can see in this example,
actually we are catching both vertebral arteries coming
together to form the basler.
And again, very deep, very far away.
And here's another illustration of that just in color alone.

Identifying Vessels in Transcranial Doppler

So how do we diagnose what we're seeing
and how do we appreciate what vessel we're in?
Again, we're gonna look at the vessel depth
and the flow direction.
The velocities are usually the highest in the MCA
'cause that is a large vessel
and they gradually taper as we go down
and out the vascular tree, you can see from a
transtemporal approach, the middle cerebral is going
to be the most shallow at a depth somewhere between 30
and 60 millimeters.
At we go a little bit deeper, we'll come to the junction
of the middle cerebral
and anterior cerebral a little bit deeper.
We'll see just the anterior cerebral.
And again, if we pivot back towards the back part
of the brain, we'll pick up the posterior cerebral
through the suboccipital window.
Again, it's the vertebrals
and vertebrals are what we're going to see first.
The basler is gonna be the deepest anywhere between eight
and 12 centimeters.
And as we see the velocities are,
are pretty much the same in the range of
around 40 centimeters per second.
And again, the flow direction normally is away from
us through the eye.
Pretty much the main vessel we're going to insulate
through the transorbital approach is the ophthalmic.
It'll be a little bit,
variable in terms of the depth
between 40 and 60 millimeters should be coming towards us.
And as we look a little bit deeper,
we can pick up the carotid siphon.
But depending on that,
where we are in the siphon,
the flow may be towards us or away from us or bidirectional,
because remember, the vessel takes a series
of turns in this region.
And from the submandibular window is primarily
what we're going to use to evaluate the ICA
Power doppler can be useful.
Obviously it picks up lower flow,
and it's a little less angle dependent.
We can see that in this image here.
If we inject contrast, we can see how much it enhances
and we can pretty much see in this example the
whole circle of Willis.
Now just another couple
of examples here is the middle cerebral artery again.
So we've got a pretty good sample volume.
We've got no angle correction on.
We're at a depth of just about six centimeters here,
which is about where we would expect it.
And we see nice,
normal looking wave form.

Diagnosing Disease: Stenosis and Vasospasm

Well, how do we diagnose disease?
Well stenosis in the intracranial vessels are going to,
is going to appear just like a stenosis anywhere else.
We'll see this focal increase in velocity.
We'll see turbulence at that site,
and we'll see a posts stenotic change in the waveform,
a drop in velocity and some turbulence.
We should expect that in general
if we see a greater than 50%,
stenosis is consistent with a doubling in the mean velocity
just like we do in the periphery where velocity ratio two
to one is a 50% stenosis.
It's the same here.
We do have some general thresholds
for the middle cerebral artery,
which we'll talk a little bit more,
a little bit more about later.
But around 100 is a good number to remember.
Well, stenosis is a problem,
but vasospasm is probably the problem we see
most of the time.
And it can occur in any of the intracranial arteries.
And it usually does follow a patient who's had a stroke due
to a subarachnoid hemorrhage.
As the blood leaks out, the body realizes that
that blood is not supposed to be there.
It reacts, it,
causes vasospasm within the vessels
because the body again senses that there is,
blood outside the vascular system
and it wants to shut that down
to prevent further leakage occurring.
Middle cerebral, anterior cerebral
and posterior cerebral are the most common sites
for vasal spasm.
And here, and we're gonna run this video here just
to show you,
the velocities
that we can see with a live,
vasal spasm.
We are peeking out over 300 centimeters per second.
If we,
if you could hear the audio,
you would hear the high pitched,
sound
that would go along with a PSV as you would expect of 300.
When neurologists look for vasospasm, they're hoping
that they can see these increased velocities,
that help predict the onset,
and precede the onset of symptoms
so they can help better manage.
There are temporal changes
that go on in these intracranial vessels.
It doesn't happen immediately
after a subarachnoid hemorrhage,
but can happen about day three or so.
Three or four velocities can increase at about a week
and then generally resolve in two to three weeks.
Most places that do this type
of monitoring repeat the transcranial doppler every day
for a, a routine interval of probably seven
to 10 days or more.
This table just shows some criteria for vasospasm.
We can see in general, a moderate vasospasm is a, with a,
within a vessel that displays a velocity, mean velocity,
again, of greater than 120 centimeters per second.
Severe vasospasm is associated once the velocities are
are above 200.
And we can see down here in the lower right, a vessel, again
with velocities well in excess of 300 centimeters per second
in severe vasso spasm.
How do we tell stenosis from vasospasm?
Again, vasospasm is not going
to be focal if we have a stenosis, it's really going
to be focal and vasospasm actually can be triggered in
multiple vessels within the brain.
And as I said, these are dynamic and will change over time.

Monitoring in Sickle Cell Anemia

Now, another area
that we use transcranial doppler transcranial imaging is the
monitoring of patients with sickle cell anemia.
Here,
patients that have distorted red blood cells,
associated with sickle cell can,
also have,
problems with getting that, that blood through
and,
into the portions of the brain.
Necessary, obviously that have,
good perfusion
and the cerebral infarction,
can be,
seen in these patients
and often quite devastating as they are,
usually younger in age.
It can occur in the distal ICA
and middle cerebral artery as well.
And if,
something is detected
and an event,
is detected
where these high velocities are recorded,
appropriate therapy can be intervened
and certainly can be helped with,
the arterial imaging.
We use just a little bit higher velocity criteria for,
somebody who's borderline abnormal.
We use a value of one 70,
but again, once mean velocities in the MCA get above 200,
it is associated with a sickle cell crisis.

Other Monitoring Uses: Patent Foramen Ovale, Emboli, and Brain Death

Now, transcranial doppler is used in a variety of methods
to do various monitoring.
And this just list a few of them looking at changes
during various operative procedures.
It also can be used to look for a patent
for Amino Valley, which has,
become quite common.
Various,
embolic events can be monitored
with transcranial doppler
and you'll see that,
we see this distortion here on the Doppler image with lots
of,
spikes.
And the, that is real, that is not due to a gain artifact.
These are just high intensity waves
that come, that come through.
And there are higher intensity compared
to the surrounding blood.
So you'll see this type
of very classic appearance on ultrasound as well
as you'll hear this chirping kind of sound
and very distinctive.
And these are referred to as hits high intensity signals.
And we'll just show you these images here.
This is a heart with agitated saline,
some bubbles going through.
We'll play that again, you can see the bubbles kind
of going through the chamber.
And we're doing monitoring, transcranial monitoring,
and we're looking for those hits.
We're looking to see if some noise comes
through in timing this out.
And we start to see a little bit, and here's a lot more.
These are the hits, these bright spiky lines that we're,
appreciating here.
And,
I'd like to thank,
bill Zang
for giving me these loops.
And here we can see some of that coming through again.
Also with transcranial doppler,
without the imaging, same thing.
We can still see, we see the various,
displays here.
And these, this is all the hits. It's not noise.
This is all the emboli coming through,
whether it's emboli from,
a procedure
or in this case, this is emboli induced by giving,
some sort of bubble
or agitated saline to detect,
in this case p Andino Valley in this equipment actually
counts the hits for us
so we can find out exactly what's going on.
Another,
purpose for transcranial doppler is basically
used to confirm brain death.
Brain death, of course, is a clinical diagnosis.
It's not going to be made by transcranial,
but transcranial will be used to detect
what the cerebral circulation is looking like
and obviously can help aid,
timing of additional tests
and also,
potentially help,
prepare
a patient who might be a potential organ donor.
And we can see these,
transcranial doppler signals showing
very high resistance flow.
Pretty much no flowed who,
through diastole.
And we would check
and,
make sure that this sort of oscillatory pattern
persists for several minutes, usually up to, you know,
at least a half an hour.
And this is just not enough circulation getting in,
to
that tissue and again, associated with brain death.

Therapeutic Applications of Transcranial Doppler

Now, the very interesting aspect of transcranial
that we will,
finish up with here is the application
of transcranial doppler in a therapeutic modality.
There've been several papers,
Dr.
Andre Alexandro has published extensively on this,
and there are some clinical trials,
and basically what happens is they use the intensity
from a transcranial signal
to help get thrombolytic agents through a clot.
Here's just a, a diagram of a clot,
and we can see the red blood cells and,
and we can see the fibrin here.
And it's described to me oftentimes as
the mechanical pressure wave from the ultrasound.
It's kind of like a breeze blowing through a curtain.
And this fibrin web is like the curtain.
The mechanical pressure from the TCD is sort
of like blowing this fibrin web around and around.
And as such, it's exposing more of this material through,
to the thrombolytic agent.
And people see things resolve a lot quickly,
quick, more quickly.
And,
I would suggest,
checking out any of these,
publications,
to get further information.
But it's a great therapeutic app,
application of TCD.

Limitations and Summary

Now, of course, any test has some limitations.
TCD is extremely operator dependent,
such
as most ultrasound, but it's pretty tricky.
We have to have good equipment.
Sometimes we're limited by patient movement.
We certainly need a, a technologist
or sonographer with a steady hand.
And as I said, in some patients, we cannot get,
proper windows and it does take a lot of time
to get a complete study.
So in summary, I think the success at doing TCD
is to be familiar with anatomy, understand the vessels,
understand what depths those vessels are, at
what direction the blood should normally be going in,
and that will help as we obtain the Doppler signals.
There are multiple clinical applications
for transcranial doppler and,
and it's expanding all the time,
and it certainly has expanded recently to include,
surgical and interventional procedures.
And lastly,
don't get a royalty from these folks,
but if you have information or need information
and have the desire to learn more about transcranial
doppler, I would recommend this book by Myra Katz
and Andre Alexandro by Summer Publishing.
It's a wonderful,
textbook
and gives you quite the overview for transcranial Doppler.
Thank you very much.