Optimizing Contrast: How to Give the Contrast Agent - SD

Introduction

My name is Paul Grabber.
I'm a cardiologist from Baylor University Medical Center in Dallas, Texas.
And I'm gonna talk today about how to give echo contrast agents for echocardiography.
A lot of people use these agents or want to use the agents, but there's some little tricks to just how to give it to get the best image quality.
I'm not gonna show you how to do that.
I'm also gonna show you some case examples of where contrast really made a difference in our patients.

Optimizing Contrast for Echocardiography

I would like to just talk a little bit about how to optimize contrast for echocardiography.
A lot of people are interested in doing contrast.
They've never done it before and nobody's ever really taught exactly how to give it and how to adjust the instrument.
So I wanna spend a little bit of time on that and then I'll go over some interesting cases that illustrate how valuable contrast can be in your laboratory.

Microbubble Contrast Agents

First of all, just a brief reminder that microbubble contrast agents are small microbubbles that are sized to pass through the smallest capillaries, which are typically about five microns in diameter.
These bubbles are on the order of two to three microns so they can get through the capillaries.
This is a picture of the bubbles shown here, and they're designed to increase the signal strength of echo because they have a different acoustic impedance than either blood or tissue, and they give quite a robust harmonic signal.

Example of Contrast Enhancing Endocardial Borders

Here's an example of an echo with poor endocardial definition.
This is actually a 3D echo, but you can't clearly see the endocardial borders here.
And so this is a patient where giving contrast can really help us.
Same patient after contrast.
Now you can clearly see the endocardial borders and you can actually trace this and get a measurement of ejection fraction and volumes that turns out to be accurate.
And studies have shown that these 3D echoes with contrast have very close correlation with MRI for volumes and ejection fraction.
So this is useful and something we do every day in our laboratory.

Bolus Administration Technique

The technique of bolus administration is shown here and we'll get to contrast infusions in a minute.
There's basically two ways to do this.
A bolus or a contrast.
If you're gonna use a bolus, you should use very tiny doses.
I find that people often think that because this comes in a one cc vial, they should give a full one cc.
Well, in fact, you can get away with a 10th of a cc or maybe up to 0.4 ccs and get a beautiful result.
You don't wanna flush this vigorously.
Most nurses are used to flushing medications into an IV by giving a 10 cc rapid flush of saline.
Well, you don't want to ever do that with contrast 'cause it'll ruin your picture and I'll show you that in a minute.
Instead, you want to give a very slow saline flush by syringe, or you want to chase the bolus into the IV just with a saline drip, and you can adjust the rate up or down to get the best quality images you want.

Risks of Vigorous Flush

Here's what happens if you do a vigorous flush, notice that you can see the apex and you can see that there's an akinetic apex with a wall motion abnormality, but you don't see the base at all because there's so many bubbles here in the apex that they attenuate ultrasound.
And you can't get any imaging of this portion of the septum or this portion of the lateral wall.
You can't really see the mitral valve at all.
And so this attenuation by an aggressive flush can make your images uninterpretable.

Infusion Technique

Now, you can also do an infusion, and this is actually my preferred technique.
I would much rather give an infusion than a bolus because as you'll see in a minute, an infusion gives you more time to image.

Definity Infusion

And here's how you give a Definity infusion.
As you know, Definity is one of two of the contrast agents approved by the FDA for use in the US.
If you'll take one vial of Definity and activate it as you normally would and then put it in a 50 cc saline bag, you can then use a dial-a-flow to drip this in and adjust the dial-a-flow to get the rate where you want it based on the quality of the images you get start around one drop per second and adjust up or down as you need to to see the imaging of the borders without obliterating the mitral annulus.
Most of the infusion pumps have rollers that destroy the bubbles, and this is why you want to use a dial-a-flow and not a typical infusion pump.
If you use too small of a needle or too small of IV, you can destroy the bubbles too.
So typically we like to use an 18 gauge needle if possible, or you can do a 22 gauge, but not any smaller than that.
Here's the infusion technique in a simple way.
This is an image taken from the American Society of Echocardiography website.
So you can look this information up on their website.
It has some useful instructions there.
You basically take a 50 cc bag of saline and you inject the Definity in and you just slowly mix it.
You don't aggressively shake it because that could destroy the bubbles, but you can squeeze it and move it around from side to side to get those bubbles in there.
And then you use the macro drip IV set or equivalent.
Again, start at one drop per second as shown here, and you can increase that if you need to to get good image enhancement.
You can even decrease it if necessary.
If you're using this for more than five minutes, it's good to reach up and squeeze the bag gently to keep it accurately and evenly mixed.

Optison Infusion

Now, you can also do an infusion with Optison.
It's a little different. Optison has got an albumin coating on the bubble, so they tend to stick to the walls of the tubing.
But you can fill the IV line with Optison and then chase it slowly with saline using either an infusion pump or a dial-a-flow.
And again, adjust the rate starting at one drop per minute and adjust it to visualize endocardial borders without obliterating the mitral annulus.
What you have to do here is gently shake the IV line or tap on it with your finger to keep the Optison from sticking to the sides and keep it evenly mixed.
It's not too hard to do, but you have to remember to do it.

Difference Between Bolus and Infusion

Here's the difference between bolus and infusion.
So a bolus where you have a rapid influx shown here and then it rapidly dissipates.
So your peak imaging time is right here, and you'd have a fairly short window for acquiring your images.
So you have sort of a minimum imaging time here.
You have higher initial concentrations and you have the probability of attenuation artifacts.
The advantage of it is as easy to do, but these things are all pretty much disadvantages.
An infusion is shown here where you have a lower initial concentration, but it's maintained for a long time.
And so this prolongs the duration of enhancement.
It gives you more of a constant level of enhancement and it has less attenuation artifacts, and of course it gives you a longer time to acquire your images.
So we prefer to use the infusion technique.

Instrument Settings for Contrast Imaging

Now instrument settings are important, and you could give a whole 30 minute lecture on this.
What I wanna say is that most of the manufacturers have preset imaging algorithms in here for contrast, and you should use 'em.
They typically use harmonic imaging.
You want to typically lower the mechanical index or the MI setting to avoid microbubble destruction.
So you might want to image with an MI setting of say, 0.3 to 0.5 instead of the typical one to 1.5.
You may need to adjust the focus, and this is important.
You wanna see the focus at the apex if you're looking for apical thrombus or wall motion, and you wanna see it at the mitral annulus if you're looking to trace LV volumes and need to see mitral leaflet insertion, and again, use the manufacturer presets for contrast.
Now they're different ones.
The manufacturers have harmonic imaging, power Doppler imaging, pulse inversion, power modulation, optical coherence imaging, ultra harmonics or subharmonics.
All of these are different. And rather than go into detail of them, I just wanna show you what they're all sort of based on using the ultra harmonic concept as a paradigm.
So if you use fundamental imaging, the fundamental signal of the tissue is shown in green and it's actually greater than the signal of contrast.
So the contrast doesn't show up as well.
If you switch to the simple harmonic imaging, then the tissue image shown in green is less than the harmonic image and you'll see the contrast.
You'll wanna set your gray scale levels and gains to sort of suppress tissue in the background.
So you can see the bubbles when they come in.
But this is the first harmonic, sort of the second.
And here's an ultra harmonic.
So here you're transmitting at 1.3 and you get a receive signal at 2.6.
At 3.6 you'll receive almost all bubble signal with very little tissue signal.
And so using this particular modality really enables you to see the bubbles well, because it suppresses tissue and looks at the bubbles.
Again, there are many different ways of doing this and each manufacturer has their own proprietary way, but it's important to use the settings that the manufacturers provide because they're all pretty good.
Now, it's important, as I said, to set the focus at the right place.
If you're trying to measure the ventricle here, you wanna see the mitral annulus so you know where to start your tracing of the ventricle.
So we put the focus at the mitral annular level for this example.
It's important to remember to do that.
On the other hand, if you're trying to not destroy the bubbles at the apex so that you can see the apex, you wanna set your focus there and you want to lower the MI setting.
And so in this example, notice the MI is lower to 0.4, where it would normally come up at something like 1.2 on this machine.
So a small thing to remember, but paying attention to those little details makes all the difference in the world and getting beautiful pictures.

Case Examples

Case 1: Revealing Hidden Apical Dysfunction

Lemme show you some case examples.
This is an apical four chamber view of a patient that was done in our lab.
And it really shows a very nice looking ventricle.
A lot of people would say, you don't need contrast 'cause the wall motion here looks pretty normal, but in fact, we gave contrast to this patient and when we did, you could see a dyskinetic apex right here.
So sometimes contrast shows you things that weren't apparent to you before.
And this is a good example of that.

Case 2: Identifying Akinetic Segments and Perfusion Defects

Here's another example of a patient who has poor endocardial border definition, particularly in the lateral wall.
It's just hard to see and it's a little bit hard to see out here in the septum.
There's a little bit of an artifact here at the apex.
So the contrast agent is given.
And when it's given, I think you can see clearly that the lateral wall is akinetic.
And not only that, but you can see bubbles inside the myocardium here, the septum, the apex, and the distal part of the lateral wall.
But there's a perfusion defect here in this wall.
And this patient had had a prior lateral transmural myocardial infarction.
So this image allows you to see the akinetic segment.
It allows you to see the absence of perfusion.
And so this is a great reason to use contrast to help you to analyze wall motion abnormalities.

Case 3: Assessing LV Function and Detecting Pseudoaneurysm

Here's another patient.
This lady had a stroke and presented to our hospital with ST elevation, but also T wave inversions that looked like this was an MI that was maybe a few days old.
And so a transthoracic echo was ordered to assess left ventricular function in the presence of thrombus.
And here's our baseline echo. It looks okay.
There's a little shadow here.
Maybe that's a thrombus, maybe not.
We decided to give contrast to see.
And here's the contrast image.
And again, you can see lateral wall moves well, the septum is hypokinetic at the base, akinetic out here at the apex, but there's no thrombus seen after we give contrast, which is quite encouraging.
On the other hand, it was a little bit surprising to see in a subcostal view that there was some contrast in the pericardial space.
And you see that right here, that doesn't belong there.
It makes us worry very much about an LV pseudo aneurysm.
So we went back, did another four chamber view and angled the picture.
And you could see right here an LV pseudo aneurysm where contrast is exiting the LV cavity into the pericardium.
And this is a surgical emergency, very important diagnosis, which almost only can be made with a contrast agent.

Case 4: Differentiating Hypertrophy from Mass

Here's another patient that we saw.
The question here is, is this some unusual form of left ventricular hypertrophy or is this a mass?
You see this bulging area right here that seems to be moving.
What is that?
Contrast can really be helpful sometimes in identifying masses in the heart.
Here's a short axis view of the same thing.
Is that just a big papillary muscle?
What in the world is that?
So we give contrast and I think you can see quite readily here, that there's a mass and that it destroys the normal endocardial border back in this posterolateral region.
And when you see a mass that destroys tissue boundaries, it's usually a malignant mass.
That this turned out to be a sarcoma, actually an angiosarcoma of the heart.

Case 5: Post-Surgical Anomaly Diagnosis

This is another very interesting case here that we saw, this patient came in and got just a standard echo.
And you can see this very unusual thing.
What in the world is this?
Well, we're gonna use contrast to help figure it out.
And it turns out that we first step is to give color flow.
And you can see that there is a little bit of color flow into this.
But it's really not clear.
Is this going from the LV or is it coming through the RV around the mass?
So we did an agitated saline study first.
Now remember, agitated saline should never cross the lungs, so you should not see it in the left side of the heart.
And sure enough, you see the right side fill, but this structure, this cavity does not fill with agitated contrast.
And nor does any appear in the left ventricle.
So whatever this is, it's not a part of the right ventricle, meaning this is not just a big moderator band, it's something else going on.
So then we give Optison, which of course crosses the left side and goes immediately into this.
Well, it turns out that this patient had spent time in prison for armed robbery.
And during the robbery he was shot in the chest.
The bullet went through the right ventricle and stopped in the LV, and the surgeon took it out from the LV apex and performed a patch to exclude the distal RV and close the hole in the RV free wall.
So this is a post-surgical anomaly that gives a very strange echo appearance.
And the patient really didn't know any of this, but the combination of saline contrast and transpulmonary contrast was very helpful in figuring it out.

Conclusion

Now, I'm gonna close there and just remind you that contrast is very useful.
You should be using it in your echo studies, and I hope this has been helpful in helping you to set the images right, to decide to use a bolus versus an infusion and to do those in the proper way because they make all the difference in the world in getting good images.
Thank you.