Hello and welcome to the basics of ultrasound for identification of lumbar anatomy. I'm actually going to talk about this in two kind of sections. I'm going to talk first a little bit about the physics of ultrasound. I'm not going to get into math. I'm not going to make you brain hurt doing any physics or anything like that because I was at best an indifferent student of physics in the past, but I think it's important that you understand the basic concepts of that. Then I'm going to talk about the kind of knobology of the machine. In other words, how do we improve the picture quality of the images that we're getting? And then lastly, very briefly, I'm going to introduce how we do this in clinical practice. Dr. Clayton is going to do a whole lecture on this live in the workshop and we'll actually do some live scanning. In addition to that, you'll have the opportunity to do some live scanning in the hands-on portion of the workshop as well. So this is really just an introduction just to talk about the basics of ultrasound. As I said, I have no financial disclosures. I have no disclosures whatsoever in this presentation. Here are the learning objectives. I will cover all of these. So let's talk a little bit about physics. So we know that sounds are waves. There are different frequencies of sound. Humans hear in this 20 to 20,000 hertz range, so low to higher frequency sounds. We know that over 20,000 hertz is considered ultrasound. We knew that mammals like bats and dolphins use ultrasound or pulse echo to locate prey, to locate their objects in their environment and those kinds of things. Actually, infrasound, which is below 20 hertz, is very low frequency sound and very low frequency sound travels great, great distances. We know that elephants can actually communicate with themselves amongst their pack up to five miles away because they use infrasound or these low frequency sounds. Now ultrasound, medical ultrasound, is much, much higher than this. So we talk about human hearing being up to 20,000 hertz. Ultrasound, we're using millions of hertz. So we're using somewhere between 2 and 15 million hertz as the frequency. So you can see that it's quite a bit different. So ultrasound is simply high frequency sound waves. They either pass through, are reflected or absorbed by tissues, and we're going to talk about each of those things. In order to generate the ultrasound wave, we have to use a probe and a machine. The machine essentially sends, is a fancy computer, it does a lot of math, and it sends an electrical signal down to the probe. The probe converts the electrical signal into sound waves, delivers the sound waves, and then it listens for the return or the echo of those sound waves as they come back into the crystals. The crystals vibrate, generate an electric signal that the computer then does funky math on and develops the two-dimensional image of the tissues that you're looking at with that ultrasound probe. Here are the different ultrasound probes. This is a linear probe. This is a high frequency linear probe. These are the kinds of probes we use for peripheral nerve blocks or for vascular access. I'm sure you're all familiar with that. This is a curved probe, a curvilinear probe. When we talk about linear probes, what we mean is that all of the crystals are in one line here. The crystals are curved, here the crystals are straight, but it's just one line of crystals. The important part of that is to remember that this one line of crystals creates an ultrasound beam that comes off of this probe, but it's only one millimeter thick, so it's essentially the thickness of a credit card. Think of a credit card sitting off of this probe. The same is true with this probe, but it's not quite a credit card because this is curved. It sends out kind of a big beam like this, but again this beam is still one millimeter thick. This is a phased array probe. We use this for transthoracic echoes, those kinds of things. This is a high frequency linear probe, so it's high frequency, which means we don't get a very deep penetration. This is a low frequency probe. We use this for abdominal exams. We can see well into the abdomen for those kinds of exams. This is a transvaginal probe. This is what we see in OB. The obstetricians use this all of the time, particularly when we're looking for antenatal instances or risk factors for antenatal hemorrhage, so placenta previa, placenta abruption, those kinds of things. They'll use the transvaginal probe. Now ladies, you are not the only ones that have to suffer this indignity. Gentlemen, the urologists have figured out that this probe exists and they are now using this probe to do transrectal biopsies of the prostate. They stick this up through the rectum and then they have a special needle guiding device and under ultrasound can biopsy very specific areas of the prostate. We all get to experience all of these different probes. I mentioned that the probe converts an electrical signal, so there's these backing materials and these electrical interfaces between the electrical signal that comes down and these crystals. Here's the crystals here in a row. They vibrate. They create the sound wave. Sound wave goes out. Sound wave gets reflected back in. These crystals listen to it. As it comes back in, it vibrates, creates the electrical signal, and that goes up to the computer. This is what those crystals look like. You can see they're very small. They're very tiny. They're actually about the width of a human hair. You do have to be careful with these probes. Treat them as if you were treating a fiber optic bronchoscope. Don't drop them. Don't bang them up against the wall. They are somewhat delicate. When we talk about sound waves, typically in order to do the math, we use transverse waves to be able to do the math. Sound waves really aren't transverse waves. They're longitudinal waves. They're mechanical waves. There is a little bit of a difference with that. What does a longitudinal wave mean? A longitudinal wave has these areas in it called compression. Areas of compression, this is a high pressure area, but it's low velocity. Then it spreads out into what's called a refraction, then a compression, then a refraction, and then a compression. This is what gives us the ability to interpret this as a transverse wave. These are what the sound waves look like as a longitudinal wave. These refraction areas are high velocity, but they're low pressure. Again, don't get bogged down in all of the math and all of that kind of stuff, but we can see if we superimpose a longitudinal wave over a transverse wave, you can see that we can figure out things like wavelength, frequencies, all of that kind of stuff. I'm not going to get into the math. Don't worry about that. Now, we're applying these waves to the body. There are different tissues with different densities and different speeds that these waves travel through them. Air is a very poor conductor of sound waves. Fluid is actually a pretty good conductor of sound waves. Then bone is actually the best conductor of sound waves. You can see when we talk about bone, it's very fast. Sound waves can travel very quickly through bone. They don't travel well through air, and that's really very evident. We all know that. If you're standing across a field and somebody's chopping wood, you can see him swing an axe and hit the wood. Then a couple of seconds later, depending on how far away you are, you hear the actual sound of the wood hitting the axe, and that's because air is a poor conductor of sound. Now, lung is mostly air, so you can see that the sound conducted through lung is very slow. Now, once we start getting to tissues, when we start talking particularly about blood, muscles, tendons, a little bit with fat, you can see these are the tissues that we're typically imaging with ultrasound. We're looking at the sonal anatomy of these tissues. You can see that the sound waves traveling through here is actually relatively close. There's not much distinction between blood muscle, muscle or tendon, or fat and tendon. This is kind of the average. This is what people will talk about, but when you get a hazy image or a fuzzy image or it's hard to discern between these different tissue planes, it's because the sound travels so closely in speed between these different ones that sometimes the computer has difficulty differentiating between the two or the three or whatever it is that you're looking for. In addition to that, you're going to notice that people on both ends of the spectrum, either very low BMIs or very high BMIs, are very difficult to image, particularly endurance athletes, people that have very low body fat indexes. So a weightlifter that's in a cut phase that has very low body fat index or an endurance athlete, a triathlete or a marathon runner, have very low. They're actually quite difficult to image only because there's really no differentiation because there's very little fat. All you really have is kind of muscle and tendon and then some nerves, and it can be very difficult to see that stuff. So both ends of the extremes for BMI can make imaging sonal anatomy difficult to interpret. Now, when we talk about penetration and resolution, when we talk about the frequency, frequency tells us resolution. So high frequency equals high resolution. Low frequency is lower resolution. The converse is true, too. High frequency is poor penetration. Low frequency is good penetration. And this kind of describes it best. So with a low frequency probe, this should actually be a curved probe. I wish they had actually made this a curved probe because typically when we're talking 2 to 5, 2 to 7, we're talking about low frequency curved probes. These are abdominal exams, deep exams. If you're doing a subgluteal or an infragluteal sciatic nerve block in a large patient, you would have to use a curved probe. Tap blocks oftentimes will have to use a curved probe. We have poorer resolution, but look, we get really good depth of penetration. So penetration is good in low frequency, but resolution isn't great. This is a high frequency linear probe. Again, really good resolution, but very little penetration. As a matter of fact, in the 12 to 15 megahertz or million hertz probes, the 12 to 15L, which is what we typically use for peripheral nerve blocks and for vascular access, the maximum penetration that we can get with these is about 6 centimeters. With these curved probes, we can get all the way down to 30. I did mention this pulse echo principle. The crystals vibrate. They send out a sound wave. It hits a bone or something, and it returns very quickly. Muscles return a little bit less. Fats even return a little bit less. It's the variation in this return or this echo that develops that two-dimensional image on the ultrasound machine. We're also going to talk about shades of gray. Everything on the ultrasound machine is going to be shades of gray with one exception, and that's the color Doppler. I'll talk about that a little bit later. So the higher the return, so the higher the echo, so bone very fast, a lot of return is going to be very bright. It's going to be white. It's going to be hyperechoic. Lung is going to be very dark. There's very low return because the air is a poor conductor, so it's going to be either anechoic or hypoechoic, and this kind of shows you those terms. I'm sure you're familiar with them, hyperechoic and hypoechoic. Isoechoic, and we typically don't talk about isoechoic. We talk about these shades of gray, and this is what the differentiation we see when we look at those ultrasound images, the sononatomy. Now, when we talk about getting the best picture, there's a couple of things that we can do as operators. We can definitely adjust gain. We can definitely adjust depth. We can definitely adjust our angle of incidence, and this is really about probe movements. We don't really adjust frequency anymore. I'll make a comment about that when we get to a couple of slides down the road, but the first generation of ultrasound machines actually let us change the frequency within the probe. The reality is all of our ultrasound machines allow us to change the frequency. I would caution you, though, in order to do that, particularly in the ultrasound machines that are specifically designed for anesthesia, it's difficult to get into the settings to do. It's not impossible. It's just difficult, and you really need to know what you're doing, so I would really encourage you, until you get very proficient at these techniques, to not mess around with the frequency. Focus comes back to our angle of incidence, and I'll talk about that. This is the knobology that I was talking about. How do we place the probe on a patient and then adjust the image so that we get a really clear sononatomy image on the ultrasound machine? I like this flowchart. It's out of the HAD6 textbook because it just gives us an idea of how we're going to adjust that ultrasound machine to get the best picture. Again, I'm not going to talk a lot about frequency because we really don't adjust it. Unless you're really into it, you can adjust it, but it's a difficult thing to do, and I would encourage you not to. We absolutely adjust gain, and that's very important. We can make it brighter or darker. We can absolutely adjust depth. Focusing is really more those probe movements. I'm going to talk about those separately. Then I did mention color doppler. We can put doppler on there. Doppler is just looking at flow. We are not diagnosing. We're not using these exams to make a diagnosis, so it really doesn't matter the flow direction and velocity. We're not making those kinds of decisions, but just know that doppler will give us color. Color is an indication of the direction of flow. Red is towards the probe. Blue is away. Again, it doesn't matter. We're not making a diagnosis. It will also tell us velocity based on the intensity of the color. There will be a velocity scale on the screen when you put doppler on there, and then you can measure velocities off of that as well. That becomes important when we start talking about transthoracic echo. More importantly, particularly if you're in the cardiac room and you're doing transesophageal echo, then absolutely flow has become very important. Direction of flow, velocity of flow, and you can measure all of that stuff with a transesophageal echo. This is one of the older machines that looked like this. It was a slider mechanism so that we can adjust gain. We could adjust frequencies. We could do all kinds of things. There's rollerballs so that we could measure a bunch of things. We could put calipers up there. It was very sophisticated. What people found out, the ultrasound manufacturers found out, is that this isn't a good model for anesthesia people. What they found out is anesthesia people, if you give them a button or dial or a lever, we're going to push it, we're going to turn it, we're going to slide it, we're going to do all kinds of things. We would mess these images up so bad because we'd mess up all of these sets on the machine that we would literally see nothing on the ultrasound. Then we'd call the rep and complain about how shitty their machine is. They would just smile and I'd come in and hit the default button, return it back to its default settings, and lo and behold, we'd have an ultrasound image. So they got smart, and they developed ultrasound machines for anesthesia, and they took most of those buttons away. So in order to make any kind of adjustments, you really have to be intentional about what you're doing. So you can see this button here. This is the gain button. We can change the overall gain. So this is a deeper exam. You can see it's 16 centimeters. This is a curved probe. What we're looking at here is likely liver. So here's the dial. We can change gain. There are some buttons here, or dots in here. I'm not going to get into the specifics of that. We can change depth here. So we can change this depth here, the depth of where we're looking at. We do have a track pad. Here's our color Doppler over here. Here's M-Mode Doppler. We typically just leave it in 2D, and for the most part, that's all we do in anesthesia is make those manipulations. Now, we can change kind of the focus, or what I call the focus, or what is technically the angle of incidence. This is kind of where the art comes in, and that ability to manipulate the probe so that you get the image that you're looking for. And really, there's four things that we can do with the probe for movements. The first I call slide. Most people call it alignment. I don't know where they came up with that. I think it's easier to talk about sliding, tilting, rotating, and then just putting pressure on. Putting pressure on is exactly what it says. In my clinical practice, my patients tend to be fluffy. I need to put a little bit of pressure on so that we can compress those tissues and get a better image on the ultrasound machine. So what do I talk about with slide? So let's say we're doing a vascular access procedure in this particular patient in his neck. We're looking for the IJ, and we're a little low, and we need to slide up. So really, all we're doing is we're not changing the orientation of the probe. We're not rotating it. We're not doing anything. We're simply moving the probe either up or down the neck so that we can get a nice cross-section or a nice short axis view of the internal jugular vein. And that's what we're doing. We're just sliding that probe up or down or left or right. If we're too far lateral out here and we don't see the vessels, we can slide the probe more medial and come in and see the carotid and the internal jugular. And that's all we're doing with slide. Now with tilt, I call it sweeping. So think of this. Remember, there is a credit card sitting off of here, this one millimeter beam coming here. And this one millimeter beam is looking kind of down here right now. So we're not even in the supraclavicular area. It's kind of just a bad area to be in. We're not really seeing what we need to see. We want to see actually this plane over here. So we just tilt the probe in this direction, which sweeps the ultrasound beam up here. And now we see a nice short axis view of the internal jugular. And that's what we're talking about, what I talk about when I talk about sweeping or sweeping that beam through my target until I get a nice view of the target that I'm looking at, whether it's a vascular structure, whether it's a nerve, a peripheral nerve, or in our case, when we're going to start talking about this, whether it's lumbar anatomy, the bony anatomy in the lumbar spine. This is another example of tilt. This is a great example. I like this. This is from an article. I highly encourage you to read this article, particularly if you're doing peripheral nerve blocks. This is the median nerve on the forearm. It's a really easy nerve to see. It's a great place to start. It's kind of a gee whiz thing for students in particular when they're very first time they're holding their probes. Very easy to image. And you can see when you're nice and perpendicular. So that's what we're seeing here. We're nice and perpendicular. We get a nice short axis view. We see the nerve really well in here. And you can actually see some honeycombing in here. And so we talk about the nerve fascicles and bundles within that nerve. It's a beautiful view. And off we go. Now, if we tilt or sweep a little bit, now we're off. We're kind of in an oblique angle. And you can see what happens is the return from the ultrasound beam is actually missing the probe. So a lot of return is going out here, but the probe doesn't get any of that. So we get dropout on the image. So we actually don't see this nerve. We don't see it very well. You see a little bit of a shadow of it. So what do we have to do? We just have to sweep our probe, our that one millimeter beam back through into the short axis view. And we can see that very nicely there. Now, rotating is simply rotating along the center of the midline or the axis, the center of axis of the ultrasound probe. And so we're simply rotating up or down or away. It's not sliding. It's simply leaving the probe on the skin and then rotating the probe around its center of gravity. And then pressure is simply pressure. You just push down a little bit harder. So now let's talk a little bit about lumbar sonoanatomy. What we're going to look for, ultimately, what we want to find is that ligamentum flabum and the epidural space. We can't see that well. Regardless of what you've heard, I've done lots and lots of these. And I'm just, I have to admit, I'm just kind of disappointed. It's the one application of ultrasound that I'm disappointed in because it just doesn't show me what I really want to. And I don't know why they use this. I put this up here because this is a really good article. I have not found an article that does as nice a job describing these techniques as I have with this article. It's a bit old. Maybe it's nobody's writing because this did such a nice job. This is actually a CT scan and not an ultrasound image. I wish they would just put an ultrasound image up there. So in my clinical practice, when I pull out the ultrasound, this is what I'm looking for. I'm looking for two things. I'm looking for spinous process and I'm looking for lamina. I'm going to describe how I do that in a second. But the reason I'm looking for lamina is I'm going to come in off of the midline. It's called the paramedian sagittal oblique view. And just out of all of those words, just think paramedium. So if this was L3-4 and this was the inner space, and I was doing a paramedian technique to access this space, I would palpate this spinous process. I would drop down a centimeter. I would come over a centimeter. My insertion point would be right here and I would attack this space at about a 20 degree angle, slightly cephalic. That's what I would do with my needle. And that's exactly what we do with the ultrasound probe. So we hold the ultrasound probe in exactly that orientation. And what we're looking for is bony landmarks. We're not going to see spinous process in this view. And people will say that all the time. I hear people say, oh, there's the spinous process. Not in this view. We do see spinous process in a different view, but not in this view. In this view, we're looking at the lamina. And so what we see is we see a sawtooth pattern of lamina. And what we can do is start down at the sacrum and simply work our way up, counting one inner space at a time until we get to the inner space that we want to be in. Then the second view that I do is I actually switch to a transverse view and I actually look at the spinous process. I want to see the spinous process. And what we see is this really dark cone. Remember this is a big bone. As the ultrasound waves hit right here, there's a bit of a reflection. So you see a flash, but when they hit over here, they bounce out this way or they bounce out this way. So there's no return. So we see a dark cone here when we're doing the midline view or the transverse view of spinous process so we can find the midline. So what does this tell me? It tells me two very important things, probably the two most important things that I need to know in order to do a good central interaxial technique. It tells me where the inner space is and it tells me where midline is. Once I know where inner space is and where midline is, I do the respi-feel and that's what I would encourage you to do as well. We cannot image this in real time, unlike a peripheral nerve block where we can actually watch an in-plane technique and see the needle come into our target area. We don't have that technology yet. I know they're working on it, but we don't have that technology yet. So this is that perimedian sagittal oblique view. This must be a lefty. It doesn't matter right or left. They've done the the thing, the nicety of marking the midline for you. You can see you're just slightly off midline looking in towards the midline and remember we're going to see those lamina as we come in. So this is the view we're coming in off of the midline. It's perimedian. We're approaching the center where the epidural space or the subarachnoid space is and again we see this lamina. We see these lamina as it marches up. There's one, there's two, and so you can see we see a lamina here, a lamina here, and a lamina here. So you can see we can literally just walk it up watching this sawtooth pattern as we go through. The inner space is between the lamina. So this is lamina. This is bone. Then there's inner space, right? That's that frame in between here. That's the articular cartilage is sitting right here, right? Those are the facet joints that you hear people talk about. In this particular view, you can actually see the dura. Sometimes you can see the dura. It's a nice bright white spot there and that's exactly what you would do with your needle as you're coming in for a perimedian technique. So here's a CT scan that shows you the same kind of thing. Again, I don't know why they keep showing CT scans. I don't find CT scans all that valuable. We certainly can't use them in clinical practice, but we can use ultrasound. So let's just look at ultrasound. So that's that transverse sagittal, excuse me, perimedian sagittal oblique view. Now we're going to switch to a transverse view and we're going to find those spinous processes because that's going to tell us where the midline is. So what we see is we see this really dark cone. I mentioned this before. So there's this dark cone here. We will often see a flash, a bright flash here. That's the actual spinous process. Then what this tells us is this is midline. Now this out here is lamina and this is lamina. So again, if you think about the ultrasound beam coming down, hitting spinous process, we get scatter here and then all of a sudden you get this cupped lamina. It's going to return some signal back to the ultrasound probe and that's what we see here. Again, if you think about the probe, the ultrasound probe hitting here and then coming back up. Now I call this the mustache sign. I think that really helps the students understand that when we're talking about it. You're not going to see that anywhere in the literature. It's something that I just kind of made up, but if you think of a nose and then the mustache sitting right here. And so what I want to see is I want to see a nice dark cone. I want to see the lamina and then I know exactly where my midline is. That's 90% of the battle and that's exactly what I do. Now there is a third view that they'll often call the bat sign and what they're trying to do is look up and actually this probe needs to be rotated this way a little bit because you want to look up into the inner space and what you see is you see the articular cartilages or excuse me the articular processes. So that's the ears of the bat and then we see a transverse process coming off to the side. Those are the wings of the bat and then when we look through here in theory we should see a nice white flash through here and that would be ligamentum flavum and then we can measure that depth. Now I know a lot of people talk about that. I don't find this view very useful. It's a difficult view to find and in addition to that what the problem with this is in my patient population is in order to get this view I'm putting pressure on here which means that if I do measure this the measurement is incorrect because as soon as I let go of the probe the skin's going to go back out and my measurement is now not correct. Now people would argue that let's say I do this view I am pressing and I measure in at seven centimeters and then I let go. I know that it's deeper than seven centimeters so I could take my needle and pretty confidently drive it in seven centimeters and then use a loss of resistance technique. I don't argue that. That's fine. I just don't find the utility in that. What do I need to know? I need to know where midline is and I need to know where the inner space is. So this is a video of me doing this on a one of my students and I'm just going to show you the technique that I use to do this. So this is that paramedian view. I'm just I worked up from sacrum. I'm just kind of counting up and so I'm coming back down so there's L3-4. I can see that space really nicely and then I mark the midpoint of the probe. I just put a dot there. Now I'm going to switch to transverse so that just kind of shows you where the dot is. Now I'm going to switch to transverse and again I'm looking for that cone sign and I'm just it doesn't matter where I find it. I'm not looking for a specific inner space. I'm just trying to find the or identify the midline and that's what I do there. I put a dot there. Now I know where my midline is. I know where my inner space is and I simply connect the dots and that's where I would go and that's how I use ultrasound. Now the one place that I do use ultrasound all of the time is if I have to do an epidural blood patch. So here's an example. This is a young lady that had had a traumatic epidural placement and an accidental dural puncture. She did have pretty significant postural puncture headache. I assessed her, talked to her about her options and she chose to have an epidural blood patch placed. I practice in a mature practice so I know that if one of my partners or one of my colleagues has already done an accidental dural puncture that they're skilled and so I don't take this lightly. I'm not cavalier about this process. The last thing I want to do is have another accidental dural puncture because that is just miserable. Now my clinical situation is different. In this particular case she's calm. She's collected. She's very cooperative. She's not having major contraction. She's not in 10 out of 10 pain. She's going to sit still for me while I do this so I do have a bit of an advantage. This is a special positioning device. We use this often. I use this all of the time. It's really nice because it lets the patient kind of get in there. It's almost like one of those massage chairs that you kind of sit in and what you're going to notice is that I let her way over rotate. I didn't have her sitting straight up. When she sat straight up she had this horrible headache so I let her way over rotate so that her headache was manageable. She was much much more comfortable doing that. So here I am. I'm just pulling the band-aid off. Now I'm just doing my scan again so I'm doing that paramedian sagittal oblique view. I'm just coming in from this side. I'm starting way low so I'm down on her sacrum and I'm just counting up to the inner space. I want to be one inner space below where that dural puncture is and then I just mark it where the midpoint of the probe is. Again now I've got my mark there. Now I turn to the transverse view. Again all I'm trying to find is the midline. I mark the midline and connect the dots and this is exactly where I went in and I was able to get in very comfortably very easily for her. Again no sedation so I'm trying to be as gentle as possible and she had a really good outcome related to that. This is actually one application where I do use ultrasound all of the time in obstetrics. Again this was just a general introduction to the use of ultrasound really to kind of cover the basic physics of ultrasound so we don't have to do that at the workshop so we can focus specifically on how to use this in clinical practice. Here are the references and again I thank you for your time.

ultrasound technology

lumbar anatomy

central neuraxial techniques

knobology

ultrasound probes

image quality

lumbar spine procedures