Hello. My name is Billy Zhang. I am the Clinical Marketing Manager at GE Healthcare and a member of the SVU Products Committee along with Terry Case and George Bordejo. This program is being supported by an unrestricted educational grant provided by the Radiology and Vascular Ultrasound Divisions at GE Healthcare in cooperation with TIP TV. I will be giving a brief overview of the SVU Professional Performance Guidelines, then Cindy Owen will follow with a comprehensive explanation of the mesoteric and renal duplex vascular examination. Cindy will then return to demonstrate these techniques on our patient model. These guidelines were prepared by members of the Society for Vascular Ultrasound as a template to aid the vascular technologist and other interested parties. The first portion of the guideline is divided into four sections. The purpose, the common indications, contraindications and limitations, and patient preparation. Duplex imaging of the renal and splanchnic arteries is performed to assess the arterial vessels to determine the presence or absence of pathology in order to facilitate clinical management decisions. The common indication sections will list the indications for each one of these exams. As an example, uncontrolled hypertension will be one of the most prevalent indications that patients will come in for the renal duplex examinations. On the mesenteric side, the indication will be slightly different. Most patients will come in with abdominal pain as a main indication for that examination. The contraindications and limitations, however, are basically the same for this examination since the vessels are located in the abdomen. Patient's body habitus will be consideration. Overlying bowel gas may hamper the examination, as well as fresh surgical incisions. Patient preparation for this type of examination is essential. Since we're going into the abdomen, it is very important that we ask these patients to fast overnight. We also would like the patients to make sure that they don't chew any gum or smoke any cigarettes prior to the exam. The SUV guidelines themselves are divided into seven sections. The first section is on patient communication and positioning, and include things such as having the patient in the supine position during the examination, and also the fact that you may have to move the patient into a lateral decubitus position to gain better access to the vessels that you're going to be interrogating in the abdomen. The next section is patient assessment. That's when you actually talk to the patient, do a brief history and physical, explain the testing that you're going to be performing on the patient, and give some guidelines to the patients on how they can help make the exam a lot easier to perform. Next are the examination guidelines themselves, and these can be used as a guide to your lab scanning protocols and internally validated criteria. The next section is reviewing of the diagnostic exam findings. This has taken place after you've completed the examination, but before the patient leaves. You want to make sure that you review all the clinical and technical data, and you document any exceptions to your protocol. Next, you want to make sure that the presentation of the exam findings is appropriate to the referring physician as well as the interpreting physician. The next portion deals with exam time recommendations, and they are divided into indirect and direct portions. The indirect portion is the portion where you actually bring the patient into the room, you set up the patient on the gurney in the supine position, you go over your history and physical, you enter things into the duplex ultrasound machine, and then the direct portion is actually when you're performing the examination. And lastly, continuing medical education. Certification is considered the standard of practice in vascular ultrasound, and with certification, you must maintain CME and keep current with any advancements in technologies or changes to your laboratory's internal protocols. With that, we're going to finish this portion and move on to Cindy's lecture, but I'd like to remind you that the current and complete SVU protocol guidelines are available online at www.svunet.org. Hello and welcome. I'm Cindy Owen. Today, we're going to talk about abdominal doppler, and our topics are going to be renal and mesenteric vascular systems. Abdominal doppler is probably one of the most challenging exams that we try to accomplish as sonographers. Our success is really dependent on some things that are out of our control, such as the patient body habitus. For example, you can see this patient right over here is really quite large, and we're seeing more and more of these patients in our practice every day. I'm going to give you some tips on how to deal with these patients. We also have patients who have very limited ability to cooperate with this. They have a hard time holding their breath. They have a hard time holding still. They may not be able to roll into positions for us. It's dependent on our experience, because with experience, we can learn how to get around some of these obstacles. It's dependent on using good technique, and we have to be very cognizant of our doppler angles. We have to pay close attention to our B-mode, our color, and our spectral doppler setup, and it's really also very important that we have modern, up-to-date equipment that gives us the tools that we need to accomplish the job at hand. Let's talk about patient preparation. We want to have all of our patients fast overnight, so they should be NPO, and then we're going to try to scan them early the next morning to minimize the bowel gas. It's okay for them to have a small amount of water for their medicine, but there's really no need to have a bowel prep for these patients, and it's recommended if they don't chew gum or smoke before the exam, although we realize a lot of that's out of our control. But if they do, then you may end up with a situation like this on your hands when you're trying to look for the mesenteric vasculature, and instead you're seeing this big echo here, which is representative of gas in the stomach. Okay, what about the technical aspects as far as the equipment? You should be reaching for your curved or sector probe, the 2-5 MHz probe, especially for the renal application. But for the mesenteric, sometimes we really have thin patients, and in those, you could try a linear array, and the advantage of that is it's going to give you better resolution, and it will also allow you to steer the beam so you can get a good Doppler angle. Up to date, Doppler equipment is very important. You want to have equipment that has an adequate high PRF or scale that's going to limit aliasing because you're going to be dealing with high velocities at depth, and that's a challenge for us. You want good color Doppler sensitivity to detect both fast and slow flow. We also need good flash suppression. Flash suppression is key in the abdomen because we have the bowel that's moving around. We have motion where the patient can't hold their breath or they can't hold still. So it's really challenging for us with our color Doppler. So flash suppression and setting up our color to optimize it so that we minimize the amount of flash is very important. And then take advantage of any imaging enhancements that your system has to offer, such as harmonics, compounding of the beam, or speckle reduction algorithms. Okay, let's talk about some of the common indications for mesenteric. We're going to be talking about a chronic arterial insufficiency in this case. These patients have postprandial pain about 10 to 30 minutes after they eat a meal, and they try to compensate for this pain by having smaller and smaller meals, and then they get a weight loss. So most of our patients have really lost quite a bit of weight by the time they come to see us, and they develop what we refer to as a food fear because it hurts to eat, so they just don't want to eat. They may have diarrhea. They may have an abdominal brui, other unexplained gastrointestinal symptoms. And because the symptoms are so nonspecific, they're usually evaluated for other types of problems beforehand, such as gallbladder disease or malignancies because of the weight loss. And many patients can have severe mesenteric arterial insufficiency, yet actually be asymptomatic because there's such a rich collateral circulation. What about coexisting conditions? Well, atherosclerosis of the mesenteric vessels is going to affect about 18% of adults greater than age 65. Most of these patients may have diabetes, positive use of tobacco, so they're smokers. They tend to have generalized atherosclerotic disease, such as carotid, coronary, renal, or extremity arteriovascular disease. It's more common in women than men, and there's also an increased incidence of AAA, or abdominal aortic aneurysm, in these patients. Okay, what about the exam components? In a sequential fashion, we're going to start with B mode. Evaluate the vessels. Look at them. Do we see atherosclerotic plaque? Where are the vessels located? And then we're going to turn on the color to evaluate the flow within the vessels. The color may show a prominent bruit. If there's a very high-grade stenosis, the bruit can be quite prominent and actually obscure the anatomy. So knowing what a color bruit looks like can be very important. And the way it's going to appear is as color outside of the vessel into the surrounding tissue that occurs during systole and disappears partially during diastole. And it's usually in the area of the post-tenotic turbulence. And since we know that bruits are high amplitude, meaning they're really strong, okay, but they're low-frequency shifts, we can reduce the impact of the bruit on the image by then sensitizing the system in such a way that we're not so sensitive for the slow flow or low-frequency shifts. So in other words, we're going to raise the PRF to reduce the impact of the bruit on the image. Overall, the color is supplying us as a roadmap for placement of our spectral Doppler sample volume. And it's Doppler, the spectral Doppler, that we're going to use to quantify the degree of stenosis. We want to keep our Doppler angle at 60 degrees or less throughout the exam. And that means that it's 60 degrees when it's measured so that we can see the angle correction cursor parallel to the walls of the vessel, not just that it reads 60 degrees. That 60 degrees has to show that the cursor is parallel to the walls of the vessel. We're going to sample in the aorta, the celiac, the superior mesenteric artery, and the inferior mesenteric artery. We're going to obtain peak systolic velocity waveforms, and we'll document post-stenotic turbulence for every high velocity that we obtain. This is very important because if we have a high velocity that may be due to a technical error, such as mis-measurement of our Doppler angle, then we're not going to see spectral broadening. So we'll only see the post-stenotic turbulence, seen as spectral broadening, following a real stenosis. We'll also look for tardus and parvus shapes, which is a delayed onset of systole. And we see these shapes to waveforms in vessels distal to the point of a high-grade stenosis. For example, if we have a high-grade celiac stenosis, we may notice a tardus and parvus shape to the waveforms in the splenic and hepatic arteries. And it's important to keep in mind that because of the collateral circulation that occurs here, it takes at least two out of the three mesenteric vessels to be stenotic for the patient's symptoms to be readily attributed to mesenteric ischemia. Now keep in mind this is a fasting study, so we don't want to do this after the patient has eaten a meal. This is done with a patient NPO because the waveform profiles that we see will change after the patient has eaten a meal. And I don't recommend doing postprandial testing, and studies have shown that it's really not that helpful. So for those of you who have a protocol that are stressing the patients with a meal as part of your exam, you can let that part go. So what about the acoustic windows that we're going to use? Well, we know the aorta is right underneath the left lobe of the liver, so if the patient has a long left lobe, that's great because that can be a good acoustic window to help us visualize the aorta, the celiac, and the SMA. If we can't get in through that left lobe, we may use oblique approaches through part of the right lobe or slightly off to the left side to try to find access so that we have a good acoustic window to see the vessels. If that fails, another tip that you can use is a semi-upright position. Have the patient just lean up on their elbows and lean back like they're sitting out in the sun, and sometimes that'll just get that left lobe down low enough that we can use it as an acoustic window. We could also have the patient sit up, and that may give us a good window, and in fact, that's an important part of the exam if we're evaluating celiac compression, which we'll talk about in a few moments. And then we use varied amounts of respiration. Sometimes visualization is best if the patient takes in a deep breath, deep inspiration. Other times, you get a better image if they blow everything out, and then for celiac compression, we're going to have to have them do both. Let's talk a little bit about the anatomy. The classic celiac anatomy that we all learned in school is really only present in about 65 to 75% of patients, so you really have to know a little bit about the variant anatomy because you are going to run across it. In the classic anatomy, we have three branches, the common hepatic, the splenic, and the left gastric that come off the celiac axis, and they can all be visualized with ultrasound. Keep in mind, the celiac is the first major branch off the abdominal aorta, and here's just three images that show some varied appearances of the celiac. This one, you can see that it's leaning off to the left before it's giving rise to the common hepatic and the splenic. This one, on the other hand, is leaning off to the right, and here's our splenic and common hepatic, and then this one is just the classic appearance that we see in our textbooks. Here in this nice netter drawing, we can see the origin of the celiac off of the aorta, and here goes the splenic artery. This is the common hepatic, and then the left gastric is just coursing up towards the patient's head. And when we compare that to a sagittal midline view, here we see the abdominal aorta, the origin of the celiac, and we're seeing the left gastric artery right here. And in this midline approach, we really don't see our splenic or our hepatic arteries. What about the waveform profile? Well, it should be low resistance. Remember, the waveform profile that we see in any vessel is representative of the vascular bed that it's feeding. So the celiac is normally feeding the spleen and the liver, both parenchymal organs demanding continuous forward supply, so continuous blood supply throughout the cardiac cycle. Hence, that low resistance flow pattern. And if you look at the waveform, you'll see that it stays well above the zero baseline throughout the cardiac cycle. So that's normal for the celiac. And it really doesn't change that much following a meal because it's not a major player in feeding the bowel or the intestine unless there is compromise of the other mesenteric vessels. Now, let's talk a little bit about the gastroduodenal artery because this is a player in our exam. The gastroduodenal artery arises from the common hepatic artery, and then it's going to course anterior to the pancreatic head. And you can see it on this ultrasound image, which is a transverse view. Here's the left lobe of the liver, IVC, aorta, left renal vein, SMA, pancreas. Here's the neck of the pancreas, where here's the portal splenic confluence, head of the pancreas. This, the letter B, is pointing to the common bile duct. The letter A is pointing to the gastroduodenal artery. The normal flow direction in a gastroduodenal artery is towards the patient's feet. So you can see in this example here, this would be a normal flow direction. It's color encoded red. The angle of the vessel is towards the Doppler beam. Flow towards the beam is represented as red, as we can see on our color scale. So that's a normal flow direction, and we can see the normal Doppler trace here of the gastroduodenal artery. Now there is a connection between, or actually many connections, between the celiac and the SMA. And the primary connection is actually through the pancreaticoduodenal arcades. There's a posterior and an anterior pancreaticoduodenal arcades. And they connect through the gastroduodenal artery. And the importance of this is that we can actually see flow go in either direction in the gastroduodenal artery, depending upon whether the SMA and celiac are normal or abnormal. In cases of celiac occlusion or high-grade stenosis, we can actually get flow from the superior mesenteric artery through the pancreaticoduodenal arcade, retrograde through the gastroduodenal artery, to then perfuse the common hepatic and splenic arteries in the celiac system. And this is such a case. This is normal gastroduodenal artery, right here seen in its long axis, with flow above the zero baseline. In this case, we see flow below the zero baseline. It's taking the flow from the SMA territory towards the celiac territory. Okay, that brings us to the superior mesenteric artery. Let's talk about that. That's the second major branch off the abdominal aorta. And it arises just below the celiac, usually about a centimeter or a centimeter and a half. But sometimes their origins are extremely close. And it's very difficult to differentiate them on the ultrasound exam. So here we see celiac, and then just below it is SMA, superior mesenteric artery. And it's going to arise just proximal to the renal arteries, which we'll talk about again in a few minutes. So it's a good landmark for locating those renal arteries. The left renal vein passes beneath the SMA and the aorta. So here's a long axis view, abdominal aorta. Here's the celiac. This is the SMA, and this is left renal vein. Here's our transverse view, aorta, IVC, left renal vein, SMA. This is the splenic vein with a portosplenic confluence. Here's our pancreas and left lobe of the liver. All right, what about the waveform profile? Now, in the fasting state, the SMA has a high resistance waveform profile. That's because it's feeding the gut. And in the fasting state, the gut doesn't really need a lot of blood flow. The arterioles are not vasodilated. They're more constricted. So if we look at the waveform profile, then we see there's very little end diastolic flow. We may even see a reverse component in early diastole. But after a meal, the gut needs more blood supply. The arterioles become vasodilated, and that's reflected in the Doppler waveform. And it looks like this. So we'll see the amount of diastolic flow increase up to about three times what it was in the fasting state. So there's a clear difference in the waveforms in the fasting and the postprandial state in the SMA, and that's important to know. All right, what about the inferior mesenteric artery? If you aren't evaluating the inferior mesenteric artery as part of your exam, you probably should. It's one of the three important vessels that can cause patients to have symptoms. It's really easy to find, and I'll show you an example when we get to the hands-on segment. But you just have to know where to look for it. It's going to arise off of the anterior left aspect of the distal aorta just before it bifurcates into the common iliac arteries. And that's about a good seven centimeters below where the SMA arises. It's gonna then course inferior and slightly to the left. And it's really commonly visible. Now, it's quite small. It's only about one to three millimeters in a normal patient. But it will hypertrophy if it's being used as a collateral source. So it could be pretty big. And this is an example of one that's hypertrophied. Here is the inferior mesenteric artery arising off of the distal aorta. Now, we're not seeing the rest of the aorta here because it's bifurcating just beyond that. And I've actually oriented my probe so that the inferior or caudal aspect of the probe is actually tilted to the left because that's the course of the inferior mesenteric artery. So the top of the probe is midline over the abdominal aorta. The inferior aspect of the probe is tilted slightly to the left. Now, if you look in this image, this is a long view of the abdominal aorta. Patient's head to the left, feet towards the right. And if we just follow it on down, right before it bifurcates, here's a tiny vessel that's then coursing off to the left. And that's a normal inferior mesenteric artery. Now, when you're looking with color Doppler, you have to be a quick look because there is very little diastolic flow here. So you'll see the IMA flash on, flash off. And since we know the diastolic component of the cardiac cycle takes more time than the systolic component, guess what? It flashes on for just a short period of time. So if you're moving your probe quickly around, you're gonna have a hard time seeing it. So it's a high resistance flow pattern in the fasting state, and it's gonna increase in both systolic and diastolic flow following a meal. And this is a postprandial state or either a state in which it's hypertrophied and being used as a collateral source. How do I know that? Well, I can look at the size of this IMA, it's pretty large. And if I also look at it, I see there's quite a bit of diastolic flow, which is not the normal state for the IMA. Now, let's talk a little bit about vascular anomalies. You need to familiarize yourself a little bit with some of the common vascular anomalies that you'll run across. One of those most common that you'll run across is a replaced hepatic artery. Now, that's when the hepatic artery actually arises from the superior mesenteric artery instead of the celiac. And the incidence occurs up to 40% of the population. And this is what it looks like. If you follow this cine clip that I have up here, we're at the proximal aorta, there goes the celiac, and we didn't see a hepatic artery. There's SMA, and here comes the hepatic artery going over to the liver. So you'll notice on the celiac, again, no hepatic artery, come down to the SMA, there goes the hepatic artery over towards the liver. So it's not that difficult to detect. What's the significance? Well, if a vessel is feeding a parenchymal organ such as the liver, then that waveform profile is going to reflect that, right? So if we look at the SMA proximal to the takeoff of the replaced hepatic artery, we'll see some diastolic flow even though the patient is in a fasting state. Now you may think that there's increased diastolic flow because there's an abnormality, but actually it's just because of this variant anatomy. So that's important to know. As we move distal in the SMA beyond where the hepatic artery came off, now we have a more typical waveform with an absence or decreased or very little diastolic flow. Other vascular anomalies involving the celiac and SMA are quite common, but each one individually may be uncommon. So here's an example of the origin of the hepatic and splenic arteries from the SMA. There's no celiac trunk in this patient, but here comes the the left gastric and the splenic and the hepatic arteries. This occurs in less than 1% of the population. Here's another one where we have the hepatic and splenic coming off the SMA and there's no celiac trunk at all. Keep in mind that some of these anomalies are going to change the waveform patterns that you see, so you need to be aware of these. There's another patient with no celiac, but in this case we actually have an hepatic and splenic artery arising directly from the aorta itself. And another example, hepatic and splenic, and here's the left gastric coming off of the splenic, but no separate celiac trunk. Let's talk about the velocity criteria. How do we determine that there's a stenosis that's 70% or greater? Well, probably the most commonly used criteria out there was developed by Gregory Mineta, and his criteria has really withstood the test of time. We're looking for a celiac velocity that's greater than 200 centimeters per second. The diastolic component will be greater than about a hundred, and here's an example. Celiac stenosis, high velocities here approaching 400 in this case, and end diastoles well over a hundred. And if you look at the waveform, you can see the windows filled in, and here we have a prominent brui that we're seeing actually in the spectral trace. For the superior mesenteric artery, greater than 275 centimeters per second with greater than 70 centimeters per second in diastole. So in this case, we have 440 centimeters per second in systole, and about 70 in diastole. And I haven't been able to really find any specific criteria for the inferior mesenteric artery, but any time we see a focal acceleration coupled with post-stenotic turbulence, we know that there's a stenosis present. So that would be good criteria. Also for the IMA, as I mentioned earlier, if you see it hypertrophy, be suspicious that it's being used as a collateral source. For all vessels, we're going to look for that focal increase in velocity coupled with post-stenotic turbulence. And we really haven't done a complete exam if we haven't documented the post-stenotic turbulence. Secondary signs of celiac stenosis can be found in the hepatic and splenic arteries, and that would be turbulence, or that tardus and parvus waveform shape. So here's our aortic velocity, and we can see that there's a normal velocity within the abdominal aorta. And in this case, in the celiac, we have an abnormal velocity with the peak systole over 400 centimeters per second. And if we want to be sure that we've really gotten an accurate or adequate velocity measurement, let's look at the splenic artery. See all this turbulence? That tells us that yes, this is a post-stenotic waveform. Same thing in the hepatic artery. The waveform profile is kind of ratty. The window is filled in. We can see some flow below the zero baseline, or in this case, above the baseline because we have a negative Doppler shift. And that's telling us that this is a post-stenotic waveform. When we go over to the SMA, we have a nice clean window right in the stenotic jet in this case, with a peak systolic velocity of almost 600 centimeters per second. But when we move the sample volume distal, that's where we're starting to see this post-stenotic turbulence. And the window is ratty, and the waveform profile is all ratty, and so that tells us post-stenotic flow. Let's move on down to the inferior mesenteric artery, 390 centimeters per second, and then here's our post-stenotic turbulence on distal. Okay, let's talk a little bit more about the secondary signs of high grade stenosis in the celiac, and that would be the flow direction in the gastroduodenal. Remember we said that was going to be an important part of this exam, is that we're just going to take a look at that when we have an abnormal celiac waveform. And here we have 550 centimeters per second in the celiac, with greater than 250 in diastole. It's jumping up to almost 700 systole, over 300 in diastole. So that should be a very high grade stenosis. Let's look at the gastroduodenal artery, and we have reversed flow here. And look at the shape of this. That's a Tardis and Parvus shape, because it's kind of a post-stenotic type waveform. So that secondary sign confirms our initial findings, and that puts all of our puzzle pieces in place, and that's important. Everything should make sense when we're doing a Doppler exam. But now there's one thing we have to keep in mind when we see high velocities in the celiac. Is it due to atherosclerotic disease, or is it due to compression of the celiac by the median arcuate ligament of the diaphragm? And that's something that can occur, and is rarely symptomatic, and must be differentiated from atherosclerotic disease. So let's look at the diaphragmatic crura. What happens is these crura arise from the vertebral bodies on each side of the aorta, and they're going to pass superior and anterior to surround the aortic opening, and then they join together by the median arcuate ligament at the aortic hiatus. The ligament's usually superior to the origin of the celiac, but in about 10 to 24 percent of patients, the ligament is low and it crosses over the proximal celiac, and a small subset of these patients can actually be symptomatic. So here we have a couple of arrows that are pointing out the diaphragmatic crura, and this is a coronal view. So you're seeing the right side and the left side, the abdominal aorta, the inferior vena cava, and then both renal arteries in this instance. Now this most commonly affects people of a young age, 20 to 40 years, more common in women than men, and it's usually in the thinner individuals that you see this. And interestingly, the celiac tends to have a characteristic indentation at its origin, or a hooked appearance, or you can think of it as kind of bent over backwards appearance. So anytime you see a celiac with this hooked appearance, or bent over backwards, that should arouse suspicion in your mind that there's celiac compression going on. And that helps us differentiate this from atherosclerotic narrowing. Now what are we going to do to evaluate these patients? Well, actually the amount of compression is going to decrease with inspiration. So we're going to scan these patients in deep inspiration and expiration, and in supine and in sitting, because the compression actually decreases in a sitting position, or upright position. If the compression persists during inspiration, then that may be correlated with symptoms, and this may be one of that small subset of patients who actually have symptoms associated with this. Also, occasionally we'll see post-genotic dilatation with these, and that usually indicates a severe compression is present. It's very rare for this to involve the SMA as well. There's been a couple of documented cases, but quite unusual. And as we know, we can get collateralization to the celiac through, from the SMA, through the pancreatic duodenal arcade, and we would look for that retrograde gastroduodenal artery in this situation. So here's a patient with deep inspiration, and we can see the celiac has a normal diameter and a normal course. But in expiration, you notice that it looks much thinner, because it's compressed, and because now we see that hooked appearance in expiration, and also some post-genotic dilatation. This is what it looks like in real time. A sagittal view, aorta, SMA. Here's our celiac, and you can see it has that hooked appearance. So we're going to obtain our Doppler waveforms in both inspiration and expiration, and we're going to evaluate the patient both supine and erect. So here's a patient where we did do such a thing, and in inspiration, the velocities were still very high. In expiration, they were a little bit higher. So we're not 100% sure, is this due to atherosclerotic disease, or is this due to median arcuate ligament compression syndrome? Well, what about if we sit the patient up? And in this case, when the patient was in an upright position, you can see the velocity is normal, and the diameter of the vessel is normal. So now we can attribute this back to the median arcuate ligament compression syndrome. All right, let's move away from the mesenteric system and talk about renal Doppler. Renal Doppler is one of my favorite exams to do. I think maybe because after all these years that I've been doing ultrasound, maybe it still provides a little bit of a challenge, which we can think of as maybe an advantage or disadvantage. Well, why are we doing these renal Doppler exams? It's because hypertension affects 65 million adults in the United States, and a small subset of these patients have renal vascular hypertension, and that's due to an obstruction of the renal arteries, and I'm talking about a vascular obstruction. And this hypertension may be corrected with treatment of the renal artery stenosis, and we're going to use Doppler to help identify these patients. So which patients are indicated? Those with progressive renal insufficiency, those with uncontrolled hypertension, chronic heart failure, stroke, heart attack, or coexisting conditions. Early diagnosis and treatment may have a positive impact on their high blood pressure and preserve renal function for the future. So where is the disease? Well, if it's atherosclerotic disease of the renal artery, that involves the proximal segment. So we're talking about the origins of both renal arteries, and that accounts for about 90% of renal artery stenosis. And you can see on this angiogram here, at the origin of both renal arteries, we have high-grade stenosis. And on our ultrasound, here's a transverse view of the aorta, the origin of the right renal artery. We can see a color brewy in the tissue around the post-stenotic turbulence of the renal artery, and this is where we typically tend to see that atherosclerotic involvement in the renal arteries. Now, fibromuscular dysplasia can also be a source of hypertension, but that tends to affect the mid-to-distal segment of the renal artery. And this is an angiogram that shows the typical beaded appearance in fibromuscular dysplasia. And this is a great image from my friend Mike Ludwig. He lent to me to show what the fibromuscular dysplasia looks like in the mid-to-distal segment of the renal artery. And you can see all these little blue circles. That indicates where we have the beads. It's like dilatations and narrowings and dilatations and narrowings. And so the color shows blue because the flow tends to swirl around in the little dilated areas where we have the beads in the fibromuscular dysplasia. Now, again, this is more common in women than men, so it's something to think about in your younger female patients that come to you with uncontrolled hypertension. But this is much less common, accounting for less than 10% of renal artery stenosis. Well, let's take a quick detour and look at the vascular anatomy. Make sure we're all on the same page with that for the renal arteries. Remember back to the superior mesenteric artery. We see the origin of the SMA. We're in very close proximity to the origin of the renal arteries, so they arise just distal to this SMA. If we turn transverse at that point, in a very easy patient, if it's our lucky day, we're going to see both renal arteries like this. In general, though, it's going to take us a little bit of manipulation of the probe and working with our color setup and to really get a good image of both renal arteries in the typical patients that we see. Now that right renal artery is going to pass underneath the inferior vena cava in its path to the kidney, and you can see it right here in the grayscale image and with color. And the left renal artery is going to be right underneath that left renal vein, so usually the first thing we see with color when we're looking for the left renal artery is this red branch, and that's actually the renal vein because it has flow that's coming towards us. And if we haven't inverted our color, we'll see the renal artery as a blue vessel, which brings me to another point. It's my personal preference that I don't use the color invert when I'm looking in the abdomen because it's impossible to make all of the arteries red and the veins blue. So instead, to avoid confusion, what I do and what I recommend is to show flow away from the beam as blue and below the zero baseline and flow towards the beam as red and above the zero baseline. The left renal vein, remember, courses between the superior mesenteric artery and the aorta, and here we see the left renal vein between the SMA and the aorta. This is splenic vein, portosplenic confluence, and inferior vena cava. And what about the anatomy as we get into the kidney? Well, we have that main renal artery. It's going to divide into segmental renal arteries right after or right before it gets to the renal hilum. And these are the large segmental renal arteries that then feed the different segments and lobes of the kidney. The segmental renal arteries are going to divide into what we call interlobar renal arteries, and those course alongside the renal pyramids. So here's interlobar renal arteries. The interlobars give rise to the arcuate arteries, which course alongside the top of the pyramids, and they're really at right angles to our sound beam. So they're very difficult for us to see and hard to get a good Doppler signal from. But then they, in turn, give rise to the interlobular arteries, and those are the ones that are in the parenchymal arteries that course right up to almost to the surface of the kidney, and occasionally you'll see one pierce the capsule, and we'll see actually a capsular vessel. Well, what about vascular anomalies that affect the renal system? Well, supernumerary renal arteries occurs in about 30% of the population, and it's very important that you understand that and learn how to look for them and make sure that you do look for extra renal arteries in every renal Doppler exam that you do, since it's so common. They can be a unilateral finding or a bilateral finding. You may see one right renal artery and three left renal arteries or two renal arteries on both sides, so that's quite variable. They usually come off of the abdominal aorta, but they can arise from the common iliac, even the inferior mesenteric artery, adrenal, or right hepatic artery. Now, we're much less likely to see those, and some of those are occurring more commonly when we have renal fusion abnormalities or pelvic kidney or something like that going on. So here's an example of a patient with duplicate right renal arteries. Looking underneath the inferior vena cava is a very useful tool, because if we see more than one little circle, then that tells us we're probably seeing more than one renal artery on the right side, and we can just follow that out laterally and see it enter the kidney. This patient actually has three right renal arteries, and we've just lined them up, one, two, three. Here's an example of a patient with one right renal artery, but two left renal arteries. Another good view to help us find patients with multiple renal arteries is to roll the patient up into a left or a right, usually the left, but either way, lateral decubitus position, so that they're up on their side, and if they're on the left side, we can use the liver as a window to look through and see the abdominal aorta. This is a great view for seeing the origins of the renal arteries and seeing supernumerary renal arteries, and in this case, we see the two left, and then this is the left renal vein right here. This is the inferior vena cava, and you can see the cruciate, the diaphragm on both sides of the aorta. The more you get used to looking at all of this anatomy, the easier it gets. This is a patient with multiple right renal arteries, and you can see here's one underneath the renal vein, and one that courses superior or anterior, actually, to the inferior vena cava, and if you look at this real-time loop from superior to inferior, here goes one renal artery, and watch out, here comes the other one, and it courses on top of the IVC, which is known as a pre-caval position. We can also see early bifurcation of the renal artery. It may bifurcate halfway down, and then you have multiple segmental renal arteries that you may need to evaluate with your Doppler, or we may have what you just saw as a pre-caval renal artery that, instead of coursing underneath the inferior vena cava, is actually on top of the inferior vena cava. We see this more often in our patients with horseshoe or mal-rotated kidneys, and these patients are more commonly having UPJ obstructions. Retro-aortic left renal veins occur in up to 3% of the population. Remember, it usually is between the SMA and aorta, and here's a transverse view aorta, and here's the left renal vein on its way over to the IVC, instead of between the SMA and the aorta, and if we put our Doppler in there, we can see that this is a venous signal. Now, it may be a little pulsatile there because of its closeness and proximity to the abdominal aorta, or it may actually be circum-aortic, which is a really a little bit more common, where instead of just going underneath the aorta, it actually wraps around it, so that's about 9% of the population, and here you see this left renal vein, and it's got a branch that's going in the expected location between the SMA and aorta, but also a branch underneath, and in color Doppler, we can appreciate that it's going on both sides of the aorta, and here in our sagittal view, here it is on both sides of the aorta, and it's quite pulsatile because it's being compressed against the spine during systole with the abdominal aorta. This patient has multiple vascular anomalies. Here we can see the left gastric artery is arising directly from the aorta instead of the celiac, and if you look closely, you can see that there's two right renal arteries here. Now, when we suspect two right renal arteries, we really do have to follow those out all the way to the aorta, and when we're doing our Doppler exam, guess what? We have to evaluate the entire length of all the renal arteries we're seeing. So here's our semiloop showing one smaller accessory renal artery, and then there's the main renal artery, and both of these have to be interrogated because stenosis in either one of those could be the source of the patient's hypertension. Now, there's two methods for detecting renal artery stenosis, and there seems to be camps that one is better than the other, but my opinion is that they're complementary, and each has its advantages and disadvantages, and I think used together, we can actually get a better exam. So there's the direct method, and this is direct Doppler interrogation of the entire length of each renal artery, including all accessory renal arteries that we find. Then there's the indirect method, and this is Doppler interrogation of the segmental or interlobar branches inside the kidney, and what we're doing there is we're going to evaluate these vessels in the kidney, and the changes we see there will be indicative of either a normal main renal artery or a stenotic main renal artery. So we're going to talk about both of these, the advantages, the disadvantages, and the Doppler criteria for both. So what are the limitations with the direct technique? Well, if we have a stenosis in one of those undetected accessory renal arteries, that's a potential cause of the patient's renal vascular hypertension, and let's face it, I mean, we can look really hard for those. We can find, I've seen up to five renal arteries on one side, but do I have confidence that I've seen every accessory renal artery the patient may have? No, I know I haven't. In many cases, I've missed them, or the patient's body habitus, or there's bowel gas, or there's, you know, limitations beyond our control, so we can't possibly always see them. We may even not even be able to image the entire length of both renal arteries. I mean, I'm telling you that you need to sample the entire length of both renal arteries, but I know that in some patients, you're going to see the proximal and then maybe the mid, and not be able to really see the distal well, or vice versa, and we, it's a compromised or not really a quite full exam, and it's important to let the physician who is interpreting this study know that this exam is not a complete exam, that there were some limitations with it, but to improve our accuracy, there are some things we can do. We must use angles that are 60 degrees or less when angle corrected parallel to the wall of the vessel, and you can use the color to help guide where the vessel walls are, because we don't always see them clearly in grayscale. We must demonstrate post-tenotic turbulence for all suspected stenoses. So, for example, if you get a really high velocity at the origin of the right renal artery, and then you don't see post-tenotic turbulence, you should really be suspicious that maybe you made a technical error. Maybe there's something wrong with your angle correction. You didn't really sample where you thought you were sampling because the patient moved, and you had your image frozen, all of those things that we have to think about, because if there really was a stenosis there, you would see post-tenotic turbulence. So, by always including that, we avoid those kind of errors, and again, we want to evaluate the entire length as much as we can of the renal arteries and all renal arteries that we see. And to accomplish that, we're going to use varied patient positions, varied probe positions to improve our acoustic windows. And we'll talk about that. So what is the criteria for renal artery stenosis with the direct method? Well, we're going to look for a renal aortic ratio that exceeds 3.5. So that's just like the ICA-CCA ratio. So we're saying that the renal artery has a velocity that's 3.5 times faster than the aorta, and that's the aorta taken right at the level of the renal artery, so the proximal aorta. We'll look for a peak systolic velocity within the renal artery that's greater than about 200 centimeters per second, and then that post-sonotic turbulence. So here's an example of a renal artery stenosis. We have a peak systolic velocity well over 500, and diastole is approaching 300 centimeters per second. There's no doubt there's a high-grade stenosis here. As we move distal, here's our post-sonotic turbulence. The normal renal arteries should show us low-resistance waveforms. They're feeding the kidneys, the kidneys are a parenchymal organ, it's demanding a constant forward flow, so we're going to see a good diastolic flow throughout the cardiac cycle. And the resistive index, the RI, should be less than or equal to .7. Okay, now, you know, beavers can hold their breath for an average of 45 minutes. Did you know that? Well, it'd be nice if we were all scanning beavers, wouldn't it? But unfortunately, we're not, because humans can only hold their breath for an average of one minute. And, of course, we're trying to get our patients to hold their breath while we're doing this exam because it's holding those arteries still for us so that we can keep that sample volume within that tiny little stenosis. Well, there's a couple of things that we can do to help us out with that. And one is that we can make a lot of our Doppler adjustments either before we have that patient hold their breath or after we freeze the image. And another thing we can do is not use a tiny sample volume. Okay, when we're, back when I started, when we used single element transducers for Doppler, we wanted to keep our sample volume like one millimeter, really small. Those days are gone. You can use a larger sample volume, and that's going to help you to stay in that one millimeter tiny residual lumen as the patient lets their breath out, which they're going to do. So this is an example of a waveform that I could freeze and then make my corrections after the fact. Or either I can make my corrections as the patient is in quiet respiration. It's going to be a big mistake if I have a waveform like this and then have my patient take a deep breath and then try to change my Doppler angle, my baseline, my sweep speed, my scale, and all of that because the patient can't hold their breath that long. And they're going to let their breath out, and I still haven't gotten my waveform in. They're only going to give me two or three good breaths, so I've got to make the best use of those that I can. So if I, after the fact, I can actually invert my waveform. I can fix my gain. I can angle correct. I can do all of those things either after the fact or while the patient is in quiet respiration. Now, it's a challenge for us also to achieve a good Doppler angle, and that's very important in Doppler because if we don't have an adequate angle, our velocities are going to be in error. So when we can see the vessel very well means that we're probably not going to have a good Doppler angle because we're almost at 90 degrees. For imaging, we want to be perpendicular. We want 90 degrees, but for Doppler, you know that's the worst angle. So in the anterior approach, which is the approach we tend to try to go to, we often get that 90-degree angle. What we can do here is actually to tilt the probe and create the angle. So instead of having the probe straight up and down like this where I am 90 degrees to the renal artery, I'm going to tilt the probe so that I slant the vessel. It's a heel-toe technique, okay, and now I have a good 60-degree angle to that origin of that right renal artery. Another thing I can do if I have overlying bowel gas in the anterior approach, which is quite common, I can roll my patient up onto either side. If I'm going to scan the right renal artery, I roll them up onto their left side, and I'm going to come in from the flank, and in this view, I'll use the liver as an acoustic window. I then see the inferior vena cava. Here's my abdominal aorta. In some cases, I'll even see it bifurcate into the iliacs, and then here's both renal arteries, and this is a great view for evaluating both origins as well as looking for supernumerary renal arteries. By the way, this is also a great view for looking for abdominal aortic aneurysms. When you have a patient with a lot of abdominal gas, the anterior approach is very difficult, so use this for looking at those AAAs as well. What about the large patients that we're getting more and more in our labs? We have to do our best by them to get a good angle, and this is a large patient. You can see by the time I'm getting down to the aorta, I'm about 14 centimeters deep, and the renal arteries are going to be even deeper than that. Well, what I do is I roll them up on their side, and I ask them to relax their abdomen and just relax it out to the side, and then I'm going to place the probe right here just above the adipose tissue and just press in. In this view, they don't push back. If I come from an anterior approach and I push hard, they push back, and they usually win the pushing contest, so it's best to try to come in from a flank approach in these cases. This is just showing how deep I would be going after those renal arteries from an anterior approach. But when I come from that flank approach, not only do I get away from the bowel gas and the adipose tissue significantly, but I also have a good Doppler angle, and I'm just really improving my outcome. And here's another view where I'm using an oblique view through the kidney, using the kidney as its own acoustic window, and I can follow the whole length of that renal artery all the way back to the abdominal aorta. So achieving the angle, this is about the oblique approach. So here's the liver, and this is not an oblique approach. This is perpendicular. So I've got a great view of the renal artery, but it's going to be a poor angle. So I'm going to change to an oblique approach, heel-toe the probe, roll the patient up a little bit, use that liver and kidney. This is transverse through the kidney, and use those as a window to see the renal artery. And oftentimes, I can see the entire length of the right renal artery in this view, and here's the vein. But now when I look at the grayscale, I don't really see it well, but I'm going to use my color to help angle correct so I have an adequate Doppler. So this is that oblique approach for the right renal artery. So what about the left renal artery? Well, I can use the kidney again as a window to see the renal artery. I'm going to roll the patient up on their right side, and I'm going to find the kidney. Here's the kidney right here. Now this is another great view for looking at the abdominal aorta for stenosis or for aneurysm, because I've shortened my distance to the aorta now, and it's really close. So once I've seen the kidney and the aorta, all I have to do is turn on my color and connect the dots and find the vessel that's in between them. So here's the color. Here's the origin of the left renal artery, and I can just follow it as it meanders back towards the renal hylum. All right, just like there's limitations with the direct technique, there's limitations with the indirect technique. So let's move from the direct into the indirect. Again, what the direct technique is doing is directly interrogating the entire length of all the renal arteries we see. The indirect technique is looking within the kidney at the segmental or interlobar arteries to get telltale signs there that there is a stenosis in the main renal artery. So indirectly, we're getting information about the main renal artery instead of directly interrogating it. Make sense? Okay, what are the limitations with that technique? Well, it can be inaccurate when the resistive index is too high. Remember the RI should be less than about .7. If it gets greater than .7 to .75, then the early systolic peak, which I'll point out to you in a moment, becomes exaggerated and the indirect technique falls apart. It also falls apart if the patient has an abdominal aortic aneurysm that's at the level of the renal arteries or superior to that. So how can we improve our accuracy with the indirect technique? Well, we have to obtain waveforms from the upper, mid, and lower poles. Just one waveform in the kidney is not going to do it. You have to do upper, mid, and lower poles. This really isn't difficult, I'm promising you, and I'll show you a little bit later. When we're looking at the interlobars or segmental renal arteries, we have to use a Doppler angle that's 30 degrees or less. Forget the 60 degree angle thing here, we've got to be 30 degrees or less. If we have angles greater than 30 degrees, then we're not going to really be able to see the early systolic peak or all the parts of the waveform. So it's key to have a low Doppler angle. We're going to use the highest Doppler frequency that we have that will penetrate. So instead of using our 2 MHz probe, we shortened our Doppler distance here. We'd rather use our 3.5 or even a 5 MHz in these cases because we're going to use a larger Doppler frequency. And guess what that does for us? It gives us a bigger frequency shift. What's the deal with that? It makes the waveform larger so we can see all of its parts. And the key to the indirect technique is that we're looking at the waveform shape. And so we want a large waveform. And then to obtain that large waveform, we're going to change our sweep speed away from the typical 4 to 5 seconds down to 2 to 3 seconds. Again, making that waveform larger. We're going to use a lower PRF so that we have a bigger waveform. And we're going to use a big sample volume size, again, a large sample volume because that patient is going to start letting their breath out. And the kidney is going to move as they let that breath out. And if you have a large sample volume, you're going to have a much better chance of staying within that interlobar or segmental renal arteries. So what about the waveforms for the normal intrarenal arteries? Just like the main renal artery, it's low resistance. And the RI should be less than 0.7. So we're going to have a low resistive index. And we're going to look at this little early systolic peak. That's this notch that we see right at the beginning of systole. That's this little point right here. And that's a normal finding. So we'll refer to that heretofore as the ESP, early systolic peak. We should see a rapid acceleration to peak systole. And we'll measure that as an acceleration time. So the acceleration to time from the beginning of systole up to the top of the early systolic peak is going to be less than 0.07 seconds. So what is our technique? We'll roll the patient into the decubitus position. That's ideal for these patients. If they can't roll, you can still do it from a supine position. But it's best to roll them. We'll scan along the posterior axillary line. And we should really have very little, if any, liver or spleen in the image. So this is an incorrect image for looking at the kidney itself for the intravessel waveforms for the indirect technique. It's a great picture of just the kidney. But it's not good for looking at the waveforms within the kidney. This is what we're after. We're going to come out more lateral along that posterior axillary line. And in this view, we have those renal vessels within the kidney coming almost straight up towards our probe. How are we going to measure the acceleration time? Well, we want to measure the time from the beginning of systole up to the peak. So this is incorrect. And it's going to give us an overestimation of the acceleration time. This is correct. We have the vertical crosshairs all the way over to the beginning of systole. And now you can see that this is a normal time. So you have to be very careful with the placement of your calipers or you'll get an incorrect measurement. Limitations occur, as I mentioned earlier, when there's high resistance in the kidney. So if the resistive index is high, the early systolic peak becomes exaggerated. And we're not going to use the indirect approach in these cases. Here's a couple of examples. Look at the resistive index. It's above 0.75. And look at the early systolic peak. It's very prominent. Here it's even more prominent in a higher resistance. So we don't want to use the indirect technique when we have high resistance flow. All right, let's talk about our technique with the intrarenal arteries. Again, we want to set that sweep speed 2 to 3 seconds. We're going to set the PRF so that the waveform fills the spectral window. We'll use a large sample volume size, a low wall filter. The highest Doppler frequency we have that adequately does the job for penetration. And our angle should be less than 30 degrees. If the angle is too steep, too large, it's hard to see the early systolic peak, as you can see in this top example. If we have a better angle, then we improve our ability to see the early systolic peak. What are the criteria for the indirect technique? Well, actually, the absence of that early systolic peak is our most sensitive criteria. And that was published by Stavros in 1994, and that's really stood pretty well over the test of time. So here's an absence of the early systolic peak, and you can see the rounded shape to the waveform. And we call that a TARDIS and PARVIS shape. So it has a delayed acceleration up to the maximum velocity. And if that exceeds 0.07 seconds, then that's an abnormal finding. This is what it looks like when it's normal. Here we have that early systolic peak. These are some examples of normal intravessel or intrarenal waveforms, and these are some examples of abnormal intrarenal waveforms. All of these are TARDIS and PARVIS shape, and you can see the delayed onset to systole. And in each of these normal ones, you can see the early systolic peak and the upright rise to systole. So let's put this all together. How are we going to do this exam when we're combining both techniques? First thing I do, a quick survey on both sides. Get the lay of the land. How many renal arteries do I see? Is this patient going to be easy, difficult? Just get an idea. I'm going to check for the visibility of those main renal arteries and any accessories. I'm going to make sure the patient doesn't have an aortic aneurysm. And then I'm going to go straight to that direct technique and directly interrogate both renal arteries. I'm going to obtain the renal aortic ratio, so I'm going to get an aortic velocity taken at the level of the abdominal aorta right at the level of the renal arteries. And then I'm going to do the indirect technique, and in doing that, I'm going to sample the upper, mid, and lower poles of both renal arteries. If the RI is greater than .75 or if the patient has an aortic aneurysm, I'm not going to use the indirect technique. I'll go away from that. And the accuracy is really improved by using both methods. So with that, I thank you very much for your attention, and happy scanning. ♪♪♪ Okay, now that we've discussed the mesenteric and the renal duplex exams, let's take a look at how we actually perform these studies. You can see my model, Cynthia, is a very slender individual, and actually she's typical for a patient that you might have for a mesenteric exam because they have that fear of food and typically have quite a bit of weight loss. On the other hand, she's not typical for the patient that you might get for a renal duplex exam. And those patients tend to be larger, and along the way, I'll give you some tips about how to handle that. But first, let's talk about the duplex exam for the mesenteric system and a little bit about the equipment. Now, because she's a small individual, I'm not going to choose my typical abdominal probe, which has a lower frequency. This is ideal for those large patients for the renal duplex exam. But for someone like Cynthia, I want a little bit higher frequency. That would be in this M7C transducer. Or I could use a linear array transducer, which has a little bit higher frequency yet and allows me to steer and get a little bit better Doppler angle sometimes when I need that capability. Okay, so let's start scanning. I'm going to put a little bit of gel right on the face of the transducer, and we'll start with a sagittal approach right at the midline. You can see the abdominal aorta, the left lobe of the liver. We can see the celiac, the first branch off of the aorta. And if you look closely, you can see this little branch that's originating from the celiac and coursing cephalad. That would be the left gastric artery. We can see that branch in a longitudinal fashion, but the other two branches that arise from the celiac aren't seen in this midline view. We would have to turn transverse in order to demonstrate them. So now we're transverse, and we see the aorta right here, and I'm going to tilt superior, and I can see the origin of the celiac. So here's my celiac trunk, and if I just tilt slightly to the left, here's the splenic artery. And to the right, here comes the common hepatic artery. Now the reason I'm showing you these two vessels is because they're very important to interrogate in patients who have accelerated velocities in the celiac, because you're going to look for secondary signs of stenosis in them. Those secondary signs would be post-stenotic turbulence, or perhaps a tardus and parvus waveform shape. So here's our transverse celiac. Let's go back to our sagittal view and look at the next branch that's coming off the aorta, and that would be the superior mesenteric artery. And it's coming off just about a centimeter, centimeter and a half below the celiac, sometimes even closer. And remember, there's a lot of anomalies here, and sometimes they'll even have a common trunk or one will be absent, and you'll see all the branches arising off of the other. Okay, now there's some other players in this exam. Remember we talked about the gastroduodenal artery? So how do we find that vessel? Well there's two ways that we can look for it. One is by just coming to the right and seeing that common hepatic artery arising from the celiac. So here's our celiac. If I go to the left, I see a circle. That's the splenic artery. If I go to the right, I see a circle. That's the hepatic artery coming over towards the liver. If I just keep following that, to the right, to the right, all of a sudden I see a branch come off of it, heading down towards her feet. Right underneath that, that's the pancreas. So this would be the gastroduodenal artery. Now remember, the normal direction of flow in the gastroduodenal artery is going to be towards her feet. So let's turn on the color and see if that's the case. Yep, Cynthia, your gastroduodenal artery is going in the correct direction. All right, let's go back to one of the other players in this exam, and that would be the inferior mesenteric artery. I told you it's pretty easy to see. It's something that you should expect to see on the majority of your patients, but again, there's two ways to find it. We'll just follow the aorta down transversely for the first way, and then just before it bifurcates, we'll see this tiny branch right here coming off. You see that tiny branch? And that's the inferior mesenteric artery. Now if I turn on my color, it might help me to see that. Watch as I just come inferior right here. That's the inferior mesenteric artery coming towards her feet right there. The other way is if I turn sagittal, now I'm at the distal aorta just before it's going to bifurcate into the common iliacs, and what I'm going to do here is just take the most caudal portion of the probe, the inferior part of it, and just tilt it to the left, and when I do that, I see a branch that's coming off the distal aorta and coursing towards her feet, and that would be the inferior mesenteric artery. Okay, so there's two ways to find the IMA, and then we discussed one of the ways to find the gastroduodenal. The other would be when we're in our transverse orientation looking at the head of the pancreas. I'm going to turn color off here for just a moment and show you the pancreas here. This is the head of the pancreas. The head of the pancreas comes right down and touches the inferior vena cava, and I can see two circles right near that, one close to the IVC and the other one a little more anterior. This one would be the gastroduodenal artery. This one would be the common bile duct, and if I turn on color, that will help to confirm that, and we can see that there is flow here in the gastroduodenal artery, but of course, we don't see any flow in the common bile duct. Okay, let's turn our color off. So we're back in our transverse view, back superior, and let's just look at the waveform profile here in the celiac trunk. So I'm going to turn on the color, and I'm going to have to increase the color gain just a little bit, and here you can see the origin of the celiac and both the splenic artery and the hepatic artery, and you can see here how both of those vessels are coursing away, so it's impossible to make all of those red because they're arteries. So again, we really shy away from using that Doppler invert in these situations. So let's put our Doppler in and look at the celiac waveform. I'm going to angle correct, and I'm very close to a zero-degree angle here, and I'm going to update just a little bit so that I really have everything oriented. I've noticed that my PRF is just about right. My peaks of my waveform are just about reaching off the end of my scale, so I may have to lower the baseline or increase the PRF just a little bit to get an optimal waveform, but any time I move my probe around, it's very important that I hit the B-Pause key to update, otherwise my Doppler angle correction is not going to match where I am in the vessel and my velocity may be in error. So I'm going to ask Cynthia to take a small breath and hold it, and I'm just going to Hit my B-Pause. Go ahead and breathe. Okay, so I have a nice waveform from the celiac, and you can see that there's a sharp upstroke in systole and a gradual deceleration in diastole, but it's a low-resistance waveform with forward flow throughout the cardiac cycle, and that's normal for the celiac trunk. Let's just take a look, say, at the splenic artery. Here we have flow going away from us. Take a breath and hold it for me. I'm going to have to increase my gain. Go ahead and breathe, and that's a typical waveform. Again, low resistance. It's taking the blood flow to the spleen. And the common hepatic artery will look almost identical to that. All right, let's go back to a sagittal view now and move down and take a look at the SMA waveform. It's going to be a little bit different. Remember, it's higher resistance. Cynthia's been fasting for me today. She hasn't had anything to eat this morning, so her bowel is not needing a lot of blood supply and diastole, the arterioles are not vasodilated. So I'm not going to expect to see a lot of diastolic flow, and that's going to help me differentiate actually between the SMA and the celiac. So I'm going to place my Doppler cursor right here in the SMA, and I'm going to go into Doppler. Okay, now, what I've done is just gotten several things adjusted. So I have my gain about right now, the PRF about right, and I try to do all that before I have her hold her breath because she's not going to have too many breaths for me. And I don't want to wear her out, make my patient too tired holding their breath while I'm making adjustment to a lot of parameters. Okay, so now, Cynthia, if you'll just take a small breath and hold it for me. Go ahead and breathe. Okay, and this is the typical waveform we would expect to see out of the SMA. It's a nice, sharp upstroke, but in diastole, you'll see it's quite different from the celiac. It's coming down to the baseline and even crossing the baseline because she's in the fasting state with very little end diastolic flow. Now, you'll see when we go down to the inferior mesenteric artery that we have an even higher resistance signal in general. Okay, so I'm just moving the probe inferior, tilting the most caudal portion of the probe slightly to the left, and here's that inferior mesenteric artery right there. And let's zoom up on that just a little bit, and even just a little bit more so you can see it better, right here. And I'm going to go ahead and adjust my angle correction and get all of those kind of things out of the way before I have my patient suspend respiration. Now, I'm going to have to move my baseline up because this has got flow going away from me. All right, I've got everything just about set up. All right, Cynthia, if you'll just stop breathing for me. Go ahead and breathe. And sometimes, you know, depending upon the patient's state of respiration, you may either lose the vessel or it may be moved slightly out of the way that you looked at it. So, don't worry about that, just be paused, let your patient breathe. If you don't see it right away, instead of kind of fishing around for it. All right, now I'm going to have you take in just a little bit bigger breath for me and hold it. All right, there's that inferior mesenteric artery. Go ahead and breathe. And that's a nice typical waveform from the IMA in a fasting state. All right, let's move on here just a little bit. So, I just want to show you quickly what it looks like if I go to the linear array transducer because I did talk about that and that's totally acceptable to do and actually beneficial in many situations because sometimes in the abdominal Doppler, it's difficult for us to get that good Doppler angle. Okay, so this is what it looks like with the linear array. Now, I actually have a mode on called virtual convex that's allowing me to have a larger field of view, which is very useful in abdominal scanning. But see what clarity I have of the celiac and the SMA. And if we turn on the color, it looks very, very nice. I can see both celiac, SMA, and the left gastric artery. And if I come down more inferior, I'm going to be able to see the inferior mesenteric artery right there. Now, you'll notice a little bit, just as the bowel moves around, we have a little bit of flashing. That's totally normal. Don't worry about it. That's just something that we have to deal with when we're doing abdominal Doppler. Another part of the anatomy you should remember is that between the SMA and the aorta lies the left renal vein. Okay, so here's the left renal vein. And when I turn transverse, I'm just going to decrease my gain a little bit. Here's the left renal vein, and it's emptying into the inferior vena cava. And then in my transverse view, just above that, here's SMA. And you can actually see several branches come off the SMA as I move caudal towards her feet. And now I'll move back cephalad. Okay, so let's move on now to the renal Doppler exam. So I'm going to switch transducers back to the M7C. Remember, on a larger patient, more typical for a renal Doppler exam, I would probably use a lower frequency transducer. All right, so let's just adjust our image. And now I'm going to go to a transverse view. Now, it's always typical for us, I think, to start in this anterior-posterior position with a patient supine. And actually, that's probably not our most successful view for renal duplex because a lot of times in the patient population that we get, there's overlying bowel gas obscuring the vessels. And so we'll have to be more inventive about finding different acoustic windows or rolling our patient up to one side or the other to get good access. But on Cynthia, we can get a good view in this AP projection. But there's other problems with it because a lot of times, it's very difficult for us to get an adequate Doppler angle. So how do we go about that? Now, if I just come down to the SMA, I know that I'm in the area of the renal arteries. And if I just look at the aorta just below where the SMA comes off, I can see there's the right renal artery. And then just a little bit further towards her feet, here's the left renal artery. It usually is just a little bit lower in its origin than the right. So let's turn on the color. Here goes my right renal artery. I'm going to turn my gain down just a little bit. And on her, I can follow it all the way down until it bifurcates towards her kidney. Now, if I want to see the left renal artery, the first thing I'm seeing is this red vessel right here, and that's the left renal vein. But once I've identified that, I know if I just go a little bit caudal to that, I'll see a blue vessel, and that's going to be the left renal artery. And it's blue because it's taking the blood flow down here towards the kidney. Okay, let's look at the Doppler waveforms that we'll get for the renal arteries. If I place my Doppler cursor in here, and I want to sample right at the origin, because remember, that's where the atherosclerotic disease occurs in the renal arteries, and that's what accounts for 90% of renal artery stenosis, atherosclerosis. The other 10% is fibromuscular dysplasia, which is going to occur out here in the mid-tudistal segment. But primarily, I'm going to be interested right at the origin. So if we angle correct it here to the origin of her right renal artery, that's not going to be so good, is it? It's almost 90 degrees. So I'm going to have to make some adjustments to get a good Doppler angle. I can either come out to the right and tilt back in at it, or I can come to the left and tilt the other way, whichever way is going to give me the best angle. And so you can see, it's just really difficult for me to get a good angle this way. So probably what I'm going to have to do in order to really interrogate the origin of that renal artery at a good angle, I'm going to have to roll her up. Okay, but before we do that, let's take a look at the left side, and then we'll roll her up so that we don't have to roll her too many times. So let's look at the typical waveform by looking at the left, because on the left here, we do have a good Doppler angle. Right here, you can see right at the origin. So let's go into the Doppler. And notice, I haven't had her hold her breath or anything like that yet. I'm just adjusting my parameters, adjusting my gain so that I have a nice, bright outline, adjusting the wall filter. Okay, so I feel like I have a pretty good setup here. Okay, Cynthia, take a breath for me and hold it, please. Fantastic. Go ahead and breathe. And this is a typical waveform. Now, I may not want the baseline in exactly that position, but it's easy for me to make such an adjustment after the fact. Also, if I want to make another adjustment to my angle correction, perhaps I'm not totally satisfied with it, I can do that after the fact. I can even adjust my gain a little bit to make it a little bit better image. I want to make all those types of changes before she holds her breath or either after I've frozen the image, because that's going to give me better time with my patient. I'm not going to wear her out, because she's only going to have so many good breaths for me. All right, let's look at some alternative windows now. Cynthia, would you mind rolling up onto your left side for me? Okay, so if I'm going to go after the right renal artery, to create an angle, I have a couple of other options. I'm going to get a little bit more gel here. One is to get a coronal view, where I can see the origins. And here you can see the aorta and both renal arteries. This would be the right, and this would be the left. But I'm really not quite optimized, because I need a little bit deeper field of view. There we go. And that's going to show it just a little bit nicer. So the right renal artery is on the top, and it's coming over here towards the inferior vena cava. Remember, it crosses right underneath the IVC on its way to the kidney. We can actually follow it out there. That's the kidney. So we saw that it did indeed go to the kidney. And then here's the left renal artery. This is a great view for looking for supernumerary renal arteries. Because you can see a long length of the abdominal aorta, and you can see if there's more than one renal artery on either side, as long as it's coming off the aorta. This is also a great view for looking at abdominal aortic aneurysms. Because in the population that we look at those, the patients a lot of times are very large. They have quite a bit of adipose tissue. You're pushing, and they're pushing back, and they win the pushing test. So if you roll them up, it relaxes their abdomen. And you can see the entire length of the aorta. And look, I can follow it all the way out to the bifurcation. And then that way, I can be assured that there's not an aortic aneurysm that I'm missing. And I can even follow those common iliacs to see extension of the aortic aneurysm into the common iliacs. Okay, enough about that. Let's look at the renal arteries. So now I can see the origin of the right renal artery. And I can see the whole length of it. Now, if this view doesn't work for me, another thing I can do is use the kidney as its own window. So what I'll do is come up here, and again, I'm gonna need just a little bit more gel. She's gonna have lots of gel by the time we're through. And I'm gonna identify the kidney in a transverse view. Okay, here's my kidney, transverse. And I'm gonna go right up to the hilum of the kidney. And at this point, I'm going to turn on my color. I can see the aorta down here. I can see the kidney. Somewhere in between there's gotta be a renal artery. So I'm gonna turn on my color. And I like to make the box a little bit long and narrow, just depending upon how I can situate the anatomy. So I've got the aorta down right here. Here's my renal artery. And I'm just gonna tip the probe until I've lengthened it out. And there's the entire length of her right renal artery. And let's see, let's just open this box a little bit wider so we can see more of it. And we can see it dividing into the segmental branches right at the hilum. So let's drop a Doppler in there again and just look at the renal artery waveform. Okay, now it's above the baseline because I actually have it coming towards me. And that's perfectly fine. It doesn't matter if it's above the baseline or below the baseline, just whichever way the Doppler shift is telling us. And what I wanna do is to just walk this Doppler all the way throughout the length of that renal artery and note any areas of increased velocity. If I actually had a patient of Cynthia's age for a renal Doppler exam, it would probably be because she has fibromuscular dysplasia. And that's when I wanna pay close attention to this mid to distal segment. All right, now that's the direct exam. What about the indirect exam? Well, with the indirect exam, remember we're looking at the vessels within the kidney, the segmentals and the inner lobars. And what we're gonna do is evaluate those vessels for signs of stenosis in the main renal artery. And we're gonna be looking at the early systolic peak and the acceleration time. So what I'm gonna do is find the kidney and I want as little liver between my probe and the kidney as possible. I want to really decrease the distance between my probe and the kidney. So I wanna bring it right up to the surface. Now, because she's such a thin individual, most of the time we see the kidney sitting right about here but hers is more anterior. So every patient is a little bit different and that's part of what makes our job so interesting, isn't it? So I'm just gonna move the probe down here till I really get a nice look at the kidney. And actually here, I'm seeing pretty nice flow in the kidney but I would be better served at this point if I actually changed my preset on the machine away from abdominal to kidney because now I'm looking at a different type of flow. I'm looking at the slower flow inside the kidney rather than the faster flow of the renal artery itself. So I'm gonna reach up here and change the preset to renal. Ah, there's the kidney. And now I'm gonna turn on the color. That's a little more like it, isn't it? That's what I expect to see, that branching pattern that's getting the flow all the way out to the surface of the kidney. Okay, so if I'm coming back here, I'm in the segmentals and then I can see the interlobars, part of the arcuates and the interlobular branches. Let's look closely at some of that anatomy. Okay, let's see if I can grab that there. All right. So our segmentals would be in this area here, the hilum. And then those are gonna give rise to the interlobars. Let me send you back just a teeny bit, right here. This would be an interlobar artery right there. And then that interlobar artery is gonna give rise to the arcuate. Well, we don't see the arcuate off that particular one, but we see arcuates right here, which are coursing on top of the renal pyramid, which is this dark area. And then the interlobulars are these fine vessels that we're seeing all the way up here to the parenchyma. And then occasionally we see some that pierce the capsule and those are the capsular branches. So these are the interlobulars, arcuates, interlobars and then segmentals. We're interested in Dopplering the segmentals and the interlobars. And for this exam, what we have to do is Doppler upper, mid and lower poles. And the reason we do that is because there may be more than one renal artery feeding the different areas of the kidney. And a stenosis in one of those renal arteries could be the source of the patient's renal hypertension. One of the advantages we have with the indirect technique is to be able to sample upper, mid and lower pole and see the effects of a stenosis in one of those arteries that perhaps we did not detect with the direct technique. Now we have to use very good technique to get good results with this. And what we wanna do is to have close to zero degrees to these vessels. We don't want 60 degrees any longer, we want 30 degrees or less. So what I'm gonna do is just watch as she breathes and I can see right here in the upper pole, I've got a couple of options where I think I can get a pretty good angle for one of her interlobar vessels. I'm gonna go on into Doppler. I've got a large sample volume so that as she breathes, I can see, keep that tiny vessel within the sample volume. All right, I have a nice big waveform. I think I'll make it a little bit larger. Notice I still haven't had her hold her breath yet. I'll lower my baseline just a little bit. That looks like that's gonna be pretty good. Maybe increase my gain just a touch. Okay, I think I'm ready then. All right, Cynthia, if you'll take just a small breath and hold it for me. Okay, I'm right there. Looks like it's gonna be a pretty good angle. Great, go ahead and breathe. And you can see a nice example right here of the early systolic peak. And that's what we're looking for. This little area and this rapid onset to peak systole. Now, we have the automatic Doppler calculations on, which is great. It's a wonderful time saver. But remember, it's just a computer. It's, you know, still there's reason for us to be here. And we're gonna have to adjust some of these calipers from time to time. So we have to pay close attention to that. It may not pick them exactly. This caliper, I want to be placed with the vertical lines right at the beginning of systole. And then my next caliper, I want to be placed right on top of the early systolic peak. And that's gonna measure my acceleration time, which you can see right up in measured by the AT right up in the upper corner. The next caliper is gonna be placed on peak systole, which sometimes is the same as the early systolic peak. And other times you'll notice it's a little bit higher. So that's fine. And then the last caliper is on end diastole. And that's used to measure the resistive index. And if you remember from the presentation earlier, the indirect technique will not work if the resistive index is greater than 0.75. Remember, it has to be less than 0.75 or the indirect technique just falls apart. It becomes invalid. Another reason the indirect technique may not work is if you have an aortic aneurysm at the level of the renal arteries or superior to the renal arteries. So here we have normal numbers, the RI is 0.59 and the acceleration time is 0.05. It should be less than 0.07 seconds. Okay, so that would be for the upper pole. Now let's look down at say the mid pole. And what I'm gonna have to do is just slide down her belly in order to get a reading so that I have a very small angle to the kidney. Turn on the color. And that's just beautiful right there. All right, so I'm gonna go ahead and put in my cursor. Here's a nice angle probably to one of those segmental renal arteries right there. I can see my PRF may be a little bit high here, so I'm gonna, or low. I'm gonna just change it just a little bit to optimize my waveform. And now I think I'm about ready. Hey Cynthia, take another breath for me. Right there is a good reading. Go ahead and breathe. Now you notice how I'll watch that. I'm gonna watch that waveform go past. Several times I'm looking for the best example that I can get of the early systolic peak. And here I don't have one that's quite as good as the one that I got in the upper pole. So what I would do clinically is I might go ahead and adjust my calipers. Okay, I can see an improvement there. I can see a little bit of an increase in my PRF. I can see a little bit of an increase in my PRF. Calipers, okay, I can see an early systolic peak here, but it's just not a great example. But I'm gonna go ahead and take this in case my patient gets sick or tired or something like that. So I'll take a picture of that, and then I'll go back and see if I can get a better example. All right. And one of the reasons I might not have a real good example is perhaps I wasn't at a very good angle for it or I wasn't in the vessel as well. All those same reasons why sometimes we try to get multiple Doppler readings to get a good example. Okay, take another breath and hold it for me. Great, and here's a nice example of the early systolic peak. So we know then that she's got a normal reading in her main renal artery. She's got normal readings for the upper and mid pole for the indirect technique, and we have a lot of diagnostic confidence in our results. One last thing I wanna show you is how do we go about getting the left renal artery? Now, on Cynthia, it was pretty easy from the anterior-posterior view, but on a lot of your patients, it's not going to be. So let me wipe off her right side, and then I'm gonna see if I can get her to roll towards me, and I'll show you what we do for the left renal artery. So if you'll just roll towards me, please. All right, let's go back here. And now I'm gonna use the left kidney and let it be its own acoustic window for me. Okay, here's her spleen. You can see the spleen, and right underneath it is the left kidney. I'm just gonna increase my gain so that I can see that kidney nicely. All right, and now I wanna increase my depth, and as I do that, I can start to see the abdominal aorta just underneath. Well, if I have the hilum of the kidney and the aorta, I know that in between there has to be the renal artery, right? So I'm gonna turn on my color. And actually now I'm looking for a faster flow again, so let's raise the PRF, or otherwise I could go back to the abdominal preset, but let's just raise the PRF here and see if we can find that left renal artery. And I'm gonna increase the gain, and there it is. And her left renal artery's a little bit tortuous. See it curve as it goes to the kidney? It's a little curvy, left renal artery, and that's not atypical. Okay, so this is what we would do to find the left renal artery. Again, you can do it in a sagittal approach, or you can do it in a transverse approach. And this is also a very good view for looking at the aorta for stenosis or for aortic aneurysm. So I hope this has answered some questions for you about renal duplex and mesenteric duplex, two of the most fun exams that you're going to encounter in your ultrasound practice. And thank you very much for your attention. Thank you.

ultrasound examinations

mesenteric vascular system

renal vascular system

Society for Vascular Ultrasound

indications

patient preparation

technical aspects

image optimization

mesenteric arteries

accurate imaging

renal artery duplex exams

renal artery stenosis

probe positions