Ultrasound Physics With Dr. Jen McPherson, Mary Baldwin University

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Step into the world of ultrasound physics with Dr. Jennifer McPherson on today’s episode! Dr. McPherson, a seasoned Certified Registered Nurse Anesthetist, former US Navy commander and Program Director of the Nurse Anesthesiology Program at Mary Baldwin University, brings her wealth of expertise to unravel the intricacies of ultrasound technology. Join us as she navigates through the fundamentals—from waveform dynamics to probe functionalities—offering a clear and insightful journey into the vital role of ultrasound in medical practice. This episode is a golden opportunity to build a strong foundation in ultrasound physics, giving you the knowledge to impress instructors and become a confident anesthesia expert!

Learn More about the Mary Baldwin University Nurse Anesthesiology DNP Program here: https://marybaldwin.edu/programs/nurse-anesthesiology-dnp/

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Have you gained acceptance to CRNA school? Congratulations! Prepare with the #1 pre-anesthesia curriculum, as recommended by CRNA program faculty. Start the NAR Boot Camp today: https://www.cspaedu.com/bootcamp

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Ultrasound Physics With Dr. Jen McPherson, Mary Baldwin University

Welcome back to the show. I am so excited about this topic, which is going to be ultrasound physics. I know it sounds complicated. What’s even more special about this episode is it’s going to be taught by the one and only Dr. Jennifer McPherson. Dr. McPherson is a distinguished, certified registered nurse anesthetist and a retired US Navy commander. Her remarkable career includes serving as an Assistant Professor and Clinical Site Director at the Uniformed Services University of the Health Sciences School of Nursing in San Diego.

In her role at the USUHS, Dr. McPherson was responsible for both didactic and clinical education of phase two of the student registered nurse anesthetist. Her expertise spans several critical areas, including pain management, critical care, ultrasound-guided regional anesthesia, and simulation. Dr. McPherson contributes to the field of nurse anesthesia. Her dedication to teaching has made a significant impact on the next generation of nurse anesthetists. She serves as the Program Director of Mary Baldwin University. Without further ado, let’s go ahead and get into some ultrasound physics.

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I’m Dr. Jen McPherson. I am the Program Director at Mary Baldwin University. In this episode, I’m going to go over the basics of ultrasound. We’ll talk a little bit about ultrasound physics, a little bit about probes and terms, knobology, and the basics to get you going and get you an idea of how we use and why we use ultrasound-guided regional anesthesia in our practice.

Ultrasound-Guided Regional Anesthesia

When I first started doing anesthesia back in 2001, we used a nerve stimulator to do all our ultrasound-guided regional anesthesia. I know a lot of you are familiar with it. It’s where we use ultrasound. We use a needle. We inject a local anesthetic into an area that will numb that body part, whether it be numbing an arm for hand surgery, numbing an ankle for an ankle reconstruction surgery, or even if it’s doing something with the abdomen when doing abdominal surgery.

When we use ultrasound, it gives us a real-time picture of what we’re looking at. When we were using nerve stimulators, it only allowed us to know where we were with the needle. We can see the anatomy in real-time. We can notice any aberrancies, and then we can see how our local distributes around the nerve.

What exactly is ultrasound? Ultrasound is a form of mechanical sound energy that travels through a conducting medium, which is tissue, and then gets reflected back to form an image. All it is is you have this sound wave going down. There’s an impedance or something it bounces off of and it comes back to form an image on the screen. That’s all it is.

Ultrasound Physics- The Waveform

First, we’re going to talk about the waveform. This really gets into some of our ultrasound physics. We have a waveform. We have a compression and a refraction. Pressure is the compression and the refraction. The wavelength is the distance between two adjacent points. If you have this compression to this compression, that’s a wavelength. The frequency is a complete cycle of compression and a rare fraction, which is a hertz. You then have your complete waveform.

When we talk about high frequency and low frequency, the higher the frequency, it produces a shorter wavelength. Remember, we said the distance is between two points. A shorter distance causes a higher frequency. For a lower frequency, we have a longer wavelength. The distance here is longer from point to point, and that gives us a lower frequency.

When we look at a probe, we have piezoelectric crystals. Those piezoelectric crystals are what form the ultrasound waves. You have your probe. You have the transducer, which converts the electrical energy to mechanical energy. Remember, we talked about that mechanical energy as the ultrasound energy.

At the end of your probe, you have your piezoelectric crystals. Those transmit and take the electrical energy from the probe. You have your cord, and then you come down. You have your electrical impulse coming down, and then you have your piezoelectric crystals right in here. These crystals transition it into mechanical energy, which is your sound energy or your sound waveform.

You have your impedance, which is an organ or what it bounces off of, and then you have your returning beam, mechanical energy, or your returning sound wave going into where the piezoelectric crystals are, which transfers it back to an electrical impulse. That takes it back to the screen, which then gives you your image. As it goes down, electrical energy goes into the transducer, and then it becomes mechanical energy through those piezoelectric crystals.

An ultrasound beam travels through tissue layers. The amplitude of the original signal becomes attenuated as the depth of penetration increases. Remember that attenuation is an energy loss. As that sound wave goes through tissue, it loses energy. It can either lose it through absorption, which is lost to body heat. You can lose it through reflection, which is where it bounces off tissues. The greater the impedance or the greater bone versus tissue versus muscle, the greater the reflection. We’ll talk a little bit more about that in a minute.

Scattering is when the ultrasound wave encounters something smaller than the wave-like fluid. That’s why when you look at a fluid-filled area, it causes that mechanical energy or that sound wave to scatter. There is no reflection. That’s why it looks anechoic or black. We’ll talk a little bit about hyperechoic, hypoechoic, and anechoic. Remember, when we talk about attenuation and energy loss, that also has to do with the impedance. The impedance is when it hits and causes a break in that sound wave.

Ultrasound Probes

We have three different types of probes. We have our linear, our hockey stick linear, and our curved array. The linear probe goes straight across. The piezoelectric crystals come straight down. For the curved array, the piezoelectric crystals go out at an angle. An important thing to note is that the linear does give you that straight-across view. It has a higher frequency, so the depth doesn’t go as deep, but it gives you a very clear view. The curved array on the other hand goes deeper. It has a lower frequency, but your visualization is not as clear. Let’s look a little more into this.

Ultrasound Physics: The linear does give you that straight across view. It has a higher frequency, so the depth doesn’t go as deep, but it gives you a very clear view.

We’re talking about the angle of incidence and the angle of insonation. We finished talking about the linear versus the curved probe. When we talk about the angle of insonation, we talk about it at a 90-degree angle. 90 degrees gives you that nice strong echo. If it’s less than 90 degrees, you’re going to get a weak echo, or if it’s greater than 90 degrees. We want to try and keep it at that 90-degree angle as much as possible to get our best visualization, whether that’s pushing down on the skin and tilting it toward or leaning it toward the object, whatever that takes.

When we talk about needle driving, the linear probe, and the angle of incidence, if we drop a needle, the angle is much less than 90 degrees. Your visualization is not going to be as good as if you could drive that needle a little further down. We then see the needle on the linear probe. Since you have those piezoelectric crystals that shoot out sound waves all the way on this curved area, it gives you a slightly better angle of incidence and a little better insonation.

Imaging

When we’re talking about structures that allow for sound wave transmission, we talked about anechoic, hypoechoic, and hyperechoic. When it’s black, it’s anechoic. We talked about that scatter. We talked about vessels and fluid. That’s what we’re talking about with our anechoic. Our hyperechoic is the same. The hyperechoic means there’s little to no transmission. Right where the bone is, it’s causing this huge impedance. That very big reflection comes back where there’s no transmission because it causes that nice hyperechoic white appearance. Whether it’s in muscles, crossbones, or through different structures, we have that bright reflection that gives us that hyperechoic appearance.

Ultrasound Physics: Whether it’s in muscles, whether it’s across bone, whether it’s through different structures, we have that very bright reflection that gives us that hyperechoic appearance.

Moving on with our hyper, hypo, and anechoic discussion, we have that anechoic that we talked about where it scatters and there’s no reflection, and there’s no impedance. Since there’s no impedance, there’s no reflection. It’s a black circle. Our fat tends to be hypoechoic, which means there is some reflection and some impedance, but it can be a light blackish with some hyperechoic areas and lines going through it.

That’s especially true of our muscles. Our muscles have those hyperechoic lines within the hypoechoic tissue. Our nerves are also a mixture. Depending on where they’re located in the body, how much impedance there is, and how thick the nerve fibers are will determine whether they are more of a hyper or hypoechoic type structure.

Orientation

For orientation, we have what we call a long axis or in-plane and we have a short axis, which is out of plane. That gives us the appearance of the tip. It may not be the tip, but it still dissects that needle when you’re looking at a short axis or out-of-plane view versus your long axis and in-plane view gives you a nice appearance.

When we look at coming in, it is called in-plane view and out-of-plane view. It’s this tip going in versus your needle. We also call it a short axis view, and there’s the tip of the needle. There is your out-of-plane. With your long axis view, the needle is coming down and coming in, or your in-plane view where you have the probe and the needle coming in-plane.

Ultrasound Machines

We will briefly talk about ultrasound machines. There are two that we usually see in anesthesia. These are ones that providers have started carrying around a lot. They’re portable. They’re easy to use. You can hook them up to an iPhone or a tablet. We have both in our program. We have the basic, big, huge ultrasound machine, and then we have the handheld ones. Finally, you have the one that we do not like to use. This is the one they use for GYN. If you have a radiology tech come and they bring this nice, big monster of a machine with them, or when you go and you have the order to have an ultrasound done through radiology, they tend to have the big giant machines.

Knobs: Gain And Depth

We’ll touch on knobs real quick. We have gain, frequency, depth, and focal length button. The two that you will use the most are gain and depth. Depth lets you visualize things deeper. Gain makes it brighter or less bright. Please don’t confuse gain with being able to see something clearer. A lot of people work on the gain to see it clearer, but all that does is make it darker or lighter. Sometimes, making it a little lighter can help you see, or making it too dark makes it too dark to see, but you want to find that fine distance between the two.

When we’re talking about depth, we’re talking about focal zone. When we increase or decrease our depth, 2 centimeters versus 3 centimeters, in the middle of the screen is where you want the object that you’re trying to look for. If you’re looking for a nerve, your nerve is in the middle. You put your nerve in the center of the screen because the beam reflection in the center of the screen is considered the focal zone, which is the optimal place to visualize your nerve.

Color Doppler

Let’s talk a little bit about color Doppler, not a whole lot. We won’t get into the weeds. If you want to distinguish between a vein and an artery, you’re going to push on it. When you push on it, you see a vein collapse and an artery keeps its form. You can use a color doppler and it will show you blue for the vein or red for the artery, but that’s not necessarily true.

What we have is what’s called a Doppler effect. The Doppler effect and the angle of insonation have to do with which way the blood is flowing and whether it’s going away from the heart or towards the heart. That’s how it perceives it as red or blue. If you’re looking at this vessel and you see they’re holding it straight and holding it upward, the way it’s coming toward the probe is showing blue. If you hold the probe downward, it shows the blood flow going this way. This way might be considered red for the artery.

It all depends on the angle of the insonation. If you hold a probe, you want to hold it so that you know that the blood flow that’s going back to the heart and the angle of insonation will show it blue versus red. Those are some in-the-weeds stuff, but the real way we want to know between an artery and a vein is whether it compresses or not.

Patient Positioning And Ergonomics

Let’s talk briefly about patient positioning and ergonomics. You want the patient to be sitting comfortably, but then you also want yourself to be comfortable. You want to ensure that you’re lined up correctly. When I say align needle, probe, and machine, this is what we’re talking about. He has the machine in front of time as well as his probe. He’s perfectly aligned to be able to watch his needle driving and watch the ultrasound machine as he goes.

When we look at clearing up, trying to visualize something, and making it clear, we talk about tilt alignment and rotation. We can call it ART, the Alignment Rotation and Tilt. Alignment means whether you’re lined up, rotation means rotating, and tilt means tilting. Those are ways that you can clear up your visualization.

That’s the down and dirty of ultrasound physics. It’s very similar to the lecture that I give our residents in our program. I am the Program Director for Mary Baldwin University. We do have open houses from July 2024 through December 2024. On the 2nd Tuesday night of every month at 7:00 PM, you can go to our website and click on it. You are more than welcome to join us. You do not only learn about our program but also learn about how to interview, what we look for in interviews, the interview questions, and what type of questions we ask. Those tend to be standard across all programs.

We talk about our requirements in our sites and everything in our faculty, but everything we give you will also help you across the board with all programs. Please feel free to join us for an open house, learn about our program, and then learn about how to apply for programs in general. Thank you for tuning in. I hope to see you at one of our open houses.

Important Links

FREE! CRNA School Interview Prep Guide: https://www.cspaedu.com/irptwqbx

Join the Free CSPA Community! Connect with a network of Aspiring CRNAs, Nurse Anesthesia Residents, practicing CRNAs and CRNA Program Faculty Mentors here: https://www.cspaedu.com/community

Get access to application & interview preparation resources plus ICU Educational Workshops that have helped 1,000s of nurses accelerate their CRNA success. Become a member of CRNA School Prep Academy: https://cspaedu.com/join

Get CRNA School insights sent straight to your inbox! Sign up for the CSPA email newsletter: https://www.cspaedu.com/podcast-email

Book a mock interview, resume or personal statement critique, transcript review and more: www.teachrn.com

Learn More about the Mary Baldwin University Nurse Anesthesiology DNP Program here: https://marybaldwin.edu/programs/nurse-anesthesiology-dnp/

Fast-Track Your CRNA Interview Prep with our CRNA Interview Crash Course! https://www.cspaedu.com/4wotmlds

Have you gained acceptance to CRNA school? Congratulations! Prepare with the #1 pre-anesthesia curriculum, as recommended by CRNA program faculty. Start the NAR Boot Camp today: https://www.cspaedu.com/bootcamp