All right thank you Karen. Um So I want to start with a little activity. So I'm gonna have everyone raised their hand, everyone raise your hand. So now if you are a physician keep your hand raised. Okay? If you do not have your RPV I keep your hand raised. Okay if you are going to take the RPV keep your hand raised. Okay so you guys should pay attention. Alright this is physics for english majors. I was an english major. Um So Physics is on the exam. It makes up about 15% of the test along with things like patient care and patient safety, quality assurance. Um and we're gonna go through most of these today. Doppler waveform characteristics. Uh one of our esteemed technologists is going to talk to you about artifacts. We'll talk about Doppler various types of Doppler and I'm not going to talk about al era but it's important to know this as low as reasonably achievable, this has to do with safety. And when we're talking about this an ultrasound, we're talking about power output. So we always want to protect our patients. Um So that's gonna be something that's important for you to know for the exam. Uh you can get a detailed content outline at this U. R. L. It's actually kind of hard to find. So if you want to take a picture, take a picture now. Okay, you can ask me afterwards too. Alright, so how does ultrasound work um for english majors? It's a little bit of a mystery. But um there's a pizzo electric crystal in the ultrasound transducer transducer that makes sound waves and these pulses of sound travel through soft tissue. Some are reflected back toward the transducer at tissue interfaces. And the position of the tissue interface is determined by the time from the transmission of the return of the pulse to the return and the strength of the signal is proportional to. I can't see my slides here, density and size of tissue causing reflection or scatter. I'm gonna slide my podium over a little bit. Okay so we put time and strength of signal together to construct a B. Motor grayscale image. And so you can see one here uh picture of an I. V. C. And a liver from an ultrasound I read just yesterday. Um So it's important to know the speed of sound and soft tissue that's probably going to be on your exam. I don't think you need to memorize this table. But sound propagation depends on properties of tissue. So uh sound propagation is less in gasses than it is in liquids than it is in solid. So when we think about a gassy bowel that obscures our view an ultrasound, that's one of the things we're talking about. Um the average speed of sound and soft tissue is 1540 m/s. Okay um I put a few equations in here and there are some equations you need to know for the test. Um So you can see here uh wavelength lambda equals the speed of sound divided by frequency. And when we're talking about frequency, we're talking about the frequency frequency of the transducer frequency is expressed as cycles per second or hertz. We hear sound in the 30 hertz to 20 kilohertz range. Medical diagnostic ultrasound is millions of hertz or megahertz, 1 to 30 megahertz. And we try to use the highest frequency possible because we get the best resolution. Um So we have better spatial detail with higher frequency ultrasound. And so you can see here on the left side of the screen, the linear probe, which we use a lot in vascular ultrasound because it gives us better resolution at the expense of penetration. So we can't see as deeply with the linear probe. And so we use this for things on the surface, carotid arteries, limb blood vessels. We use the curvilinear probe to look deeper in the abdomen and we get better penetration. But at the expense of resolution. So your pictures aren't as good. So Doppler ultrasound. This is really incredibly important in a lot of our applications in vascular ultrasound. So Doppler effect is the, when the siren coming towards you sounds different from the siren going away. That's the change of frequency in a detected wave when the source or detector is moving. And so the Doppler shift occurs when reflectors. So things like red blood cells or other moving parts move relative to the transducer. And the frequency of echoes for moving reflectors is higher or lower than the frequency of the transducer depending on whether motion is toward or away from the transducer. So you can see here the Doppler equation, that frequency shift or change in frequency is twice the flow velocity um Times cosine theta divided by C. So when your angle is zero. Like in echocardiography with flow directly toward the transducer. Co sign zero. Yeah the cosine of zero is one. So you get a maximum Doppler shift. If the angle is 90° you get the cosigner zero, so you get no shift. And that's why if you have a blood vessel in a probe directly perpendicular to it, you're not gonna see anything. So it's important to know your various types of Doppler. So we have continuous wave Doppler, it's a continuous wave of sound. Um The filtered output is produced as a sound or a tracing. So this is our handheld Doppler that we use at the bedside. Um And this is great at detecting flow but reflectors or scatters anywhere in the beam can contribute to the signal. Um So it's not very specific. So pulsed Doppler allows us to discriminate singles signals at different depths and allows for detection of reflectors or scatters in a defined sample volume. So you can see in the little tiny picture of the blood vessel on the left. We have uh the cursor with a a little couple of perpendicular bars. That's this. The sample volume. And so we're detecting the flow in this pop little artery only at that sample volume. Power Doppler. We also use our color power angio. This is used to detect low flow states and it does not provide information about velocity or direction. So this is really important for things like endo leaks and pseudo aneurysms and other really low flow states. You think you have an occluded carotid? So you're gonna put the power Doppler on it, but it doesn't tell you anything about what direction that flow is going or how it's flowing. We put this all together in vascular ultrasound in the form of a duplex ultrasound. So this is real time B mode or grayscale imaging with Doppler. I want to talk a little bit about direction of flow, on on color. Doppler. So um color is very arbitrary, so it's not fixed. We can flip the color. Um And so I, for me, I have come up with a way to figure out the direction of flow that that works for me. So what I want to know is first of all, where is the cursor pointing? So in this picture, which I think is it's a vertebral artery, you see the label there um by convention, the head is to the left, the feeder to the right of the screen. And the probe in this case is pointing toward the head. And so flow that is toward the probe um is going to be positive and flow away from the probe is going to be negative. And so I actually, this was a picture I looked at really early in my career and I was so confused as to why it was presented this way because it's a very abnormal looking for tibial artery and then I realized it's retrograde. So the flow is negative, it is away from the probe. Okay, so obviously really important for the test to be able to understand direction of flow and it can be challenging at times, particularly in arm veins. So, spectral analysis. That's your Doppler waveform, every red blood cell. This is how I like to think about it. Every red blood cell has it's own velocity and direction. Okay, so the Doppler waveform is all of those red blood cells in a given sample volume superimposed upon each other. So that's how we get our spectral window. So when flow is laminar, all of those red blood cells are going in the same direction at the same velocity and they are very neatly superimposed to give you this nice crisp picture with that black spectral window. Um If you imagine that you widen your sample volume, which you should not do in most applications, um you're gonna get a lot more um disordered flow and that can cause spectral spectral broadening. Um That's not what this is, That's a diseased vessel, but you can see all of those red blood cells are just going around like crazy in this turbulent artery and that produced this messy shaggy waveform. So I want to talk about wave forms and I do want to talk a little bit about terminology because there is a recommendation to change some of our terminology. Um So uh we talk a lot about try physic biphasic and mono physic wave forms and there's a lot of heterogeneity in how people describe wave forms. And so we are encouraging everybody to use the terms multiphasic for try physic and biphasic waveforms and mono physic for mono physic wave forms. And so we'll show you some of these normal wave forms and abnormal wave forms. So if we look at the left panel at the top we see a wave form that is anti grade. And it is multiphasic. So you have a component above the baseline, below the baseline and back above the baseline. The second wave form is retrograde and I would say that that is mono physic because there's no component that moves across the baseline. This 3rd 1 is a little unusual because it's truly bidirectional flow. So I wouldn't necessarily call it multiphasic. It is multiphasic but it's bidirectional. So that's where you've got an incomplete steel. And then the bottom one of course is an absent um flow. And then here you can see on the other side as well, some normal and abnormal wave forms that are described as multiphasic and mono physic and then finally resistant. So this is going to be really important um depending on what bed of the circulation you are in. So typically peripheral arteries are high resistive and so that means they have very little flow in diastolic or no flow in diastolic. Um And so you can see in the left panel a normal high resistive and a probably abnormal high resistive waveform and then a low resistive waveform. So tissues that need a lot of blood flow like the brain and the kidneys, you'll see um a lot of flow and ds Tole. And so you can see here a normal and a an abnormal low resistive waveform. Just a word about aliasing. Um This will probably be on your test. Um So uh pulse repetition frequency is the number of pulses emitted by the transducer over time. And there's this thing called the Nyquist limit. So that's your um P. R. F. Divided by two. So when we think about how we transmit sound into tissue and how we receive it, we need to have enough time for the sound to get back to the receiver. And so if our Doppler frequency shift exceeds the Nyquist limit then we're going to get aliasing. And so you can see that on the left panel. The waveform is wrapping around the screen. And so we need to change our scale to be able to get an accurate representation of what this waveform looks like. So same blood vessel in panel A and b. One is just with a scale set a little higher. Now this is an example of aliasing that's um it's not an artifact this is a stenosis. Um But we can also see color aliasing. Um If we if we uh have R. P. R. F. Set too low so finally velocity. So all of diagnostic ultrasound in the carrot seeds and in the peripheral arteries is based on velocities. That's how we figure out stenosis. And um the velocity of blood flow varies inversely with total cross sectional area of the vessel to a certain point. And so you can see on this curve um We have velocity on the X. Axis with the decrease in diameter of the blood vessel or degree of stenosis on the Y axis. I have my exes reverse. Excuse me. Um And so you can see that as that blood vessel decreases in diameter stenosis increases until we get to a certain point and then we fall off that curve. So we see this in things like carotid arteries where you have a critical stenosis, like an almost 100% stenosis. You're going to have very low velocities. And so that's important to think about on your exam. And with that I will sum up. Thank you very much
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