How to Optimize Your Duplex Studies - SD

Optimizing Duplex Studies: Spectral Doppler Display

This presentation is about how to optimize your duplex studies.

First, before we start our discussion, we are going to look at when you obtain a spectral doppler, what information is displayed on the screen. And for that, if you look on the top right hand corner, you notice that we are at 56% Doppler gain. Our wall filter is setting low at 60 hertz. The sample volume, our gate is set at 1.5 millimeter. The map that we are using for this spectral display is two. On this particular system, we are using a seven megahertz linear probe. We know it's a linear probe from the display in our image, and we are at two centimeter depth obtaining this spectral display.

Now the key information, how to get this nice, clean, crisp, spectral display is the core of our discussion within the next 15, 20 minutes.

Cursor or Doppler Line Placement

So let's start. First, what is cursor? Cursor or doppler line? We use this to place a doppler line over a 2D image and depending on what type of transducer you are using, if you're using a linear probe, the options that you have is you can place this cursor straight, you can move this cursor, steer that cursor to the left, or steer this to the right. If you're using a linear probe, the options that you have is you can place this cursor straight, you can move this cursor, steer that cursor to the left, or steer this to the right. And if you're using a curved probe or you're using a sector probe using your track ball, you can move this cursor radially from side to side.

Important concept here is where to place this cursor because this is going to have a direct impact on how you are getting the information. Now, if you draw imaginary line in the axis of the vessel and you draw another imaginary line in the axis of the cursor, notice that these two lines are perpendicular to one another. So what that means is if you look at this spectral display, it is somewhat ambiguous. In other words, this is not as diagnostic than as we want. Now the reason is these two lines are perpendicular, but if I change and reduce the angle, now you notice this angle is about 45 degree. Now I'm not perpendicular and look at the end result. Now I get a very nice crisp signal as a result. So you do not wanna be perpendicular the less angle that you create with in regards to the cursor and your vessel, that is the optimal way to look at the vessel of interest.

In this example, let's say we are looking at the celiac trunk. So before I activate my pulse doppler, I am going to actually place decide what approach it would be best for me to take an optimal alignment. So depending on if I'm coming from the top or if I'm coming from the bottom, it would be once I choose which approach I can take, then I will act activate my pulse. Doppler. Let me show you another example.

In this particular example, we are looking at aorta and we are looking at the right renal artery, the proximal portion of the right renal artery. Notice that we have a lot of noise, we have a lot of our gain is way too high and we are aliasing here. What the sonographer did here is actually place the cursor angle correct and somewhere in here she decided that would be, this would be a best approach to take the reading from the proximal portion of this vessel. Now let's take a look at this signal. This signal by its appearance, it is telling us that we are not really at the area that what we think it has the tight stenosis, some of this flow is below the baseline. You notice that this white area, it's coming all the way to the baseline, that it is indicative that there is a stenosis but proximal to the point that we are taking. And this was just a guess that the sonographer took when she took this image.

Now by optimizing this is where we started. By optimizing our settings, we reduced the gain, we increased our PRF, now we have a better visualization of the vessel. Now we can more accurately place the cursor and our angle correction. Notice now we are getting much, much better reading and our reading now is 360 centimeter per second, which is the indicative of the tight stenosis.

Sample Volume or Gate

The next area that we need to look at is the sample volume or gait. This sample volume or gait, it determines the location and the area that the pulse weight. Do Doppler listens for a returning signal. Now you can increase or you can decrease the size of your gate. This range is anywhere between one and a half to 30 millimeter. In general, we increase the gates when you are searching for flow. In other words, if you are looking at a very small vessel and you are not getting the signals that you're looking for, it's okay to open your GA a little bit. But we reduce the size of the gate for precise information. In general, we use smaller ga for the arteries we use larger gait for the venous flow.

Notice again, in this particular examples here, when you open the gate wide open, look what happened to the inside of the envelope. We are overs saturating inside of this signal when we close our gate. Notice that how nice and crisp and clean the signal is. So you always want to keep your sample volume somewhat smaller only if needed. You open that up. In this particular example, I am at the high limb of the spleen and I'm showing you the both splenic artery and vein. Now if I have difficulty to getting, depending on what I'm looking, whether it's the artery or vein, if I have difficulty to getting the information I want, it's okay to open up a little bit. Notice I'm getting both of these signals and that's okay. If I'm interested in venous, I'm going to ignore the arterial signal signal and vice versa.

One of the things that is going to be very helpful is when you're doing, abdominal studies, especially venous, I opened the gate a little bit bigger, usually do not want exceed in the size of the vessel. And by opening the gate to this size, I am getting a better reading rather than keeping my gate small. Another thing, notice what I did. I took two steps. First, I identified the area of the interest. I magnified that area, put the cursor. I am happy that I am not perpendicular to the vessel. I have a good angle in relationship to the vessel. Now I activate my spectral doppler and I get a good result.

So one of the questions is what is the recommended size of the sample volume? And the recommended size is in general, you should not be any larger than about a third of the size of the vessel. If your sample volume is larger, the sample volume is capturing slower flow that occurs near the vessel walls. Another thing to keep in mind is an example that I'm showing you here. Sometimes it can be challenging whether or not if this area, this end diastolic component that I'm not getting a good representation. Is that for real or do I have a reversal of the flow? The important thing is where and how this signal was obtained. If you're looking at this example, you notice that the gate was placed closer to the wall of the vessel. Ideally, you wanna place this in the middle, not close to the wall, and that way you are sure that you are certain that you are not missing part of the cycle.

Angle Correction

We are moving on into the angle correction. Notice this is the same vessel, but I am showing you two different velocities in this particular example. I'm not angle correcting and I'm getting about 56 centimeter per second. In this example I did angle correct and I'm getting a reading of about approximately a hundred centimeter per second. In this approach, the system thinks we are in the vessel. In other words, by not angle correcting the system assumes that the angle is zero degree. But here we, we are telling the system that the angle of incident is about 56 degree and this is going to be for any time. When you're interested in measuring the velocity, we need to angle correct.

It is another thing to remember is when you are angle correcting, you wanna be always parallel to the wall of the vessel. That is very important to remember. In this example I am showing you, here's the vessel, this is the renal artery, here's the vessel. Notice the next step. When I do on the freeze frame, I angle corrected. Now I am parallel to the wall of the vessel. This practice should be done in real time, not on the freeze frame because your end result can be you may get, a false information.

In this example, I am showing you a graph. I am getting a reading of about 130 centimeter per second. What is happening here? Here is the axis of the vessel. Here is my angle correction. Now I'm going to magnify this area. Notice the angle between what I initially decided to be my angle correction. This angle is very different than this angle. In other words, this is not the axis of the vessel. Remember I told you earlier that the angle correction should be parallel to the wall of the vessel. So now we are going to correct this and now we are parallel to the wall of the vessel. Now note what velocities I'm getting about 70 centimeter per second.

Another thing is very important is when you are looking in certain studies in this particular example, lower extremity Venus, notice that I did not angle correct. There is no need for angle correction in this particular study. The reason for that is the shape of the wave form rather than the velocity. It's going to be used for interpretation in this study. Since I'm not interested in velocity, this is one step that I can omit from my examination.

So remember in short you do angle correction only when you are measuring velocity. You use cursor when you want to align an optimal alignment between the vessel axis and doppler scan line. Another thing to remember, sometimes people mistaken and they're thinking that they need to make this gate parallel to the wall of the vessel. Different manufacturer use their gate and they use that a little differently. So this gate, it has nothing to do with your angle correction. Just imagine your gate to be a little hole in your doer line and you just move that up and down along your doppler line and you place that in the area of the interest with the gain in spectral doppler, just like your 2D gain, this controls the amplification of the returning signals.

Doppler Gain

When I turn my doppler gain too high, notice that not only I'm introducing this background noise, notice what is happening into the envelope. It is oversaturated. You bring down your gain to the point that you eliminate this background noise. Now look at the net result, a very nice clean signal. Another thing you have to be very conscientious about is if you oversaturate your gain setting. Potentially you can get falsely slight elevation on your velocity readings. In this particular display, the gain is too low. In this end of the spectrum, the gain is too high and you can see that I am getting slightly higher reading compared to where my gain was too low. So pay very close attention to how much gain sitting. When you see this background noise, your gain sitting most likely is sets too high.

Velocity Scale or PRF

This is a very important part of the doppler studies velocity scale or PRF. By definition, PRF is the rate at which your transducer is pulsing per second. Anytime you change your PRF by increasing or decreasing the range of the display velocities is also automatically adjusted by your system. When you increase your scale, you make your waveform the size of the waveform smaller. When you decrease your scale, your the size of your waveform gets bigger. When and why do you wanna do this? Let's say you, you have very high velocities and you are aliasing. So by increasing my PRF, now you can fit your spectral display very nicely and you can correct your the, the aliasing. And this is an example of such a case. This is the top of the signal I am wrapping around. I'm aliasing. One way to correct this is by increasing my PRF automatically the machine is adjusting my velocity range and now I can fit this very nicely into the spectral display.

Speaking of aliasing, just as another take home point for you, in order to correct aliasing in spectral display, you can adjust your baseline. Perhaps bringing it a little bit low. As I already indicated, you can increase your PRF or your scale. You can decrease your depth, decrease your frequency, or increase your doppler angle. All of this will contribute to, it will correct the alias in, in venous studies. It is very important that you pay attention to your PRF because if you increase your PRF too high potentially by first look, it may appear as this is in, in the cases of the occlusion on the portal, system in this case splenic vein. Sometime if there is a total occlusion, this may appear as an artifact, but in reality I created this by decreasing my PRF. This is exact same signal. Now notice we have a better visualization of this display,

Wall Filter

the wall filter, this is one, parameter that it suppresses velocities associated with tissue or wall motion. But the trade off for this is if you don't pay close attention and you start, changing the wall filter a lot, it can potentially eliminate diagnostic information. Example is in this case, I'm showing you another example of in this lower extremity arterial system and you notice that we have this biphasic flow, although this is not showed very well, but this is a biphasic flow in lower extremity biphasic or phasic, it's considered normal when you see a monophasic flow that is not normal. But in this case, I bumped up my wall filter too high, and by bumping my wall filter too high, I eliminated this weak echo. So I mask a very important piece of information. I made a a normal vessel look abnormal.

Sweep Speed

Another thing is sweep speed. This controls how quickly the spectral information is updated. In this particular example, I slow down my sweep speed. We were doing a valvular incompetency examination and by slowing down my sweep speed, I am showing the normal flow. As soon as the patient performed Val Salva, now we are getting the reverser of the flow. And as soon as patient now breathing normal, we are back to normal. So in one display I am showing all the sequence of the events. Otherwise, in general, when you go to your spectral display, the system default is in normal or moderate default. Now I need to take one or two or three pictures to illustrate that. By slowing down my sweep speed, I can show all these changes in one picture in the studies when it's done for patency of the palmer arch. For the radial artery. Notice again, by slowing down our sweep speed, I can show all the changes. Here is before the pressure on the radial artery here is increasing velocity. Here it goes normal. You notice that again for the interpreting physician. This is going to be much, much faster and easier to visualize all these changes in the studies for, thoracic outlet syndrome. Here is when the patient is in neutral position, I am getting a nice biphasic flow, which is expected. And as soon as we place the patient's arm in the symptomatic position, notice now this, the wave form is changing. It's gradually changing to monophasic. We have elevated velocity and as soon as we bring the arm down into the neutral position, it goes back to the normal. Again, you don't have to do this, but it's going to show all these changes, very nicely in one image.

In the other end of the spectrum, if you increase your sweep speed, this is going to be very important on the studies or in the areas that let's say patient cannot hold their breath for a long time or if you are scanning the patient that you need to get this information quite rapidly. In the normal sweep speed. This is the intraparenchymal studies of the kidney. Notice that we are displaying about approximately five cycles. So sometimes it's going to be difficult for the patient hold their breath for a long time, increase your sweep speed. All you are doing is now we are capturing one or two cycles. The temporal information is improved. So this would be a very helpful, technique.

Tips for Optimizing Pulse Doppler

So in general, if you have difficulty to getting the information that you're looking with your pulse staler, this is your cheat sheet, pay very close attention to the angle, to the flow. In other words, you do not want to be perpendicular to the vessel. That is the cursor that I'm referring to. Pay attention to your wall filter you in general, especially for the abdominal studies. You want to keep your wall filter low, not high. You want to increase your doppler gain. Without introducing too much of background noise, pay close attention to your PRF, keep it low without introducing aliasing your gait, your sample volume. If you have difficulty getting the information, increase that slightly without going beyond the actually diameter of the vessel. And last, not the least, is the frequency of the translucent that you're using, especially for the abdominal studies. If you are going, if you are using a high frequency transducer that may not, you may not able to penetrate deep enough. So try to reduce the, frequency of the transducer to a lower range.

So it is, as you can see, all this information that I presented to you is going to help you to gather a good information, which is going to be very important for the interpretation. Thank you.