How To: Transcranial Doppler - HD

Transcranial Duplex Study: Transtemporal Approach

So today we're lucky enough to be performing a transcranial duplex study, using the Transtemporal approach.

And Scott is going to be actually performing the exam and we'll be talking about what we're visualizing on the screen.

We start out with the gray scale display, and then we will use the intracranial landmarks to then help us know what we are looking at with the intracranial anatomy and the vasculature.

So we'll begin by focusing with the transducer positioned on the temporal window.

And Scott is angling ever so slightly to optimize the gray scale display and to document the intracranial bony landmarks.

And we will be using the landmarks to help us know sort of where we are and where to position the color box for displaying flow of the vascular anatomy.

Now Scott's gonna talk as well and tell us what he is looking at on our perfect model.

And obviously, and the clinical setting.

Your patients may not always be this cooperative and they may not be this young and have good temporal bones, but this really is a wonderful demonstration of how well you can visualize the intracranial anatomy.

It's really quite remarkable so that even in an optimal, a suboptimal patient, we can probably get very good results.

And these landmarks are where we're gonna start with the petris and sphenoid bones.

And as we angle is when I turn color on, I'm gonna expect to see the crowded siphon in this area, and we'll do a little adjusting with the transducer to go ahead and get the siphon.

That's beautiful.

It certainly makes it easier to have that color display when you're trying to identify the vasculature that just blindly looking for a signal.

And we'll go ahead and throw a pulse Doppler on here.

Now we are using a transducer.

This is using a frequencies of between five and one megahertz.

Okay, So we will go ahead and sample this.

So this system has an actual transcranial software package so that the mean velocity is gonna automatically be calculated when you place the envelope follower in place.

And it will be optimizing the signal for TCD.

Let's come out of health Doppler and we're just gonna angle the transducer and come up into the circle of Willis looking at the MCA and the a CA.

Just turn the color gain up a little bit.

Now as with non-imaging, we can tell the difference in the vasculature based on flow direction.

So the color is very helpful in not only demonstrating the course of the vessel and the curves and the position of the vessel, but also the flow direction.

So we can clearly see the middle cerebral artery, which is the larger and the more robust of the vessels, and then the anterior cerebral artery moving towards the midline.

In addition, you can actually see the contralateral a CA in MCA as well.

Visualizing the Middle Cerebral Artery (MCA) and Anterior Cerebral Artery (ACA)

Now, Scott has positioned the sample volume within the middle cerebral artery.

You can see a nice envelope follower, a nice spectral display, and even a little bit of a reverse flow here where he's picking up a probably a branch vessel.

So the sample volume depth is at about five centimeters that you can see the display of the peak systolic velocity as well as the end diastolic, which are also used in the overall calculation of the data.

But the mean velocity or the time average peak is 58 centimeters per second.

And as I walk shallower with the sample volume, we're coming up into the M two segment, which is right around here.

And you can see it on gray, on color Doppler very easily as far as where the M1 and M two segment.

That's beautiful. So now if you change the size of the sample volume, you could just show the.

There you go. So if I decrease it, I came down to a sample volume size here of four millimeters and we're up in the M two segment.

But normally most of the literature has used a fairly large sample volume because it helps you find the vessel and track the vessel more easily.

I think if you make the sample volume so small, you're looking for small vessels and having a small sample volume is really just gonna make it much more difficult.

So a fairly large sample volume is usually optimal.

Take that back to seven and a half and we're gonna now come down, we've sampled the MCA all the way out.

We're gonna come down and look at the MCA to a CA and this should be bidirectional flow showing both vessels.

Mm-hmm. And as I take my sample volume slightly deeper, we will drop into the a CA.

So this is really the most repeatable and reliable intracranial landmark, and it's what we always go back to as really the resource for knowing where we are and what we're evaluating.

This is the area where we would expect to find increased velocities in children with sickle cell anemia or in patients with vascular disease.

Because as we know at bifurcations, that tends to be the point at which we have higher velocities.

So that's beautiful. We can go To the distal a CA also here.

So you can really track that a CA quite a distance, can't you?

Mm-hmm. Okay.

So that helps you make sure that you know that you followed the a CA and that you've tracked it to the midline.

And that's as far as we're gonna go.

Okay. Now can you show me again the ICA?

Because that's really a critical vessel and one that's very difficult to evaluate with the non-imaging.

There we go. So it almost is circular elliptical and because you've angled a little inferiorly, an angle, a Little inferior. Mm-hmm. And I did a small clockwise rotation of the transducer very slightly.

Okay. Okay.

And you can hear a little harshness there in the ICA, which is what we normally expect.

A little bit of baseline disturbed flow there as well.

Okay. That's beautiful.

Posterior Circulation

Okay, We'll go back to our landmark and now we will angle posterior.

I'll move my color box and look at the posterior branch.

Now posterior segments,

So the reason this is important is that it, in the days before we had the beautiful images, we would sometimes follow the PCA if it was carrying a lot of collateral flow and miscall it as the middle cerebral artery.

So we found that it was very helpful to know that we had documented the anterior and the posterior circulation separately.

So that shows the top of the basler where the basal artery has bifurcated into the P one section segments of the PCA.

And then there you can see the color differentiation.

And then as the vessels wrap around the brainstem, you can see that they actually appear to change direction too because of their angling Start here at midline.

So once again, at the midline, we have a almost a bi-directional signal again, because if we increase the size of the sample volume, you actually can get both PCAs at that point so that you can see the PCA mean flow velocity is much lower than we saw in the middle cerebral artery.

And that's another hallmark sign that you have actually separated the anterior and the posterior circulations.

Very Nice. I'm just angling.

Okay. So that would be the P two SEC segment.

That's really nice. Um, so if we could just go back and show them sort of the course of the MCA mm-hmm.

And changing the color box and showing how that impacts the quality.

So if we were doing a full clinical exam, we would track through the entire course and take samples at each at what do you usually do?

Four millimeters, two four millimeters.

Because with the nine image you couldn't see, so we did 'em at two.

But with the imaging, because you can visualize the vessel, I think four is probably adequate.

It's also very easier too to, with visualization of the vessel.

You can walk it right through the sample volume. Mm-hmm.

Exactly. Pinpoint the exact area where you have the highest velocities. Right.

Okay. If we narrow our color box here, we will see better frame rates and you're actually increasing your color sensitivity.

So if you had a patient who had vasospasm or a very tight stenosis, this might help you optimize the signal better.

I'm just gonna increase my color PRF slightly to reduce some of the aliasing at the peak cyst leak in the MCA,

Actually see some of the branches in the MCA out there in that distal portion.

That's Very nice. So should we go posterior?

Yes. We'll try posterior Turn up on your side.

So when you wanna evaluate the posterior circulation and look at the vertebral basilar system, you just have the patient turn down to your chair, turn to their side, and tilt their chin to their chest so that you can actually open up this area and have them relax so that it doesn't get, the muscles don't get too tight.

So you're actually shining the trans, the ultrasound through the opening of the frame and magnum And just searching around looking for the best window.

Mm-hmm. And once you have your vessels, you can just turn on your transducer two, be able to follow those into the skull.

They're, That's beautiful.

Okay.

Very nice.

So the sample volume is at about 5.5.

So you can see the peak s sicily in the posterior circulation is quite a bit lower than the anterior circulation, which is what you would expect.

Then you could just track the vessels.

And depending on the patient presentation, whether they're a vascular disease patient, you may want to look at the vertebrals in the Vassar, whether it's just documenting flow with the TCD study for as a baseline.

So there are the vertebral, vertebral, just not really seeing any.

Here we go. There it was. Yeah.

Alright. Very nice. Okay.

Orbital Examination

So when we're doing the orbital exam, particularly in children, if you find it necessary to do it, it's good to put the gel over the on the transducer.

Now I do have an orbital preset on the system that I can go into.

Mm-hmm. That will automatically reduce my power levels.

Okay. So we're using a mechanical index of 0.1. Alright.

And if we need be, we can go lower.

Oh wow. That's beautiful.

So we're positioning the transducer over the eye, the closed eyelid and angling so that we can evaluate the flow in the ophthalmic artery.

Wow, that's beautiful.

So normally when the flow is coming up, the ophthalmic artery is the first branch of the internal carotid.

So the flow would be towards the transducer coming out of the orbit.

If the ophthalmic is serving as a collateral, then we would see actually a reversal in this signal.

This can also be used to track the ophthalmic into the siphon and evaluate the carotid siphon.

Particularly if you have an older patient who has a very thick skull and you can't get a good signal, you can actually evaluate the siphon.

But I would imagine with the imaging systems, that you really don't encounter that problem too much anymore.

You can generally assess the temporal window.

Very nice. So that would be a complete transcranial imaging exam.

Thank you, Scott. Thank you.