Procedures are challenging enough without having to worry about fiddling around with your ultrasound machine, too. In this video, you'll be introduced to the nuts and bolts of understanding ultrasound modes, how to scan for procedures, and using the various Doppler functions available.
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[00:00:00] Now, we will discuss the different modes of ultrasound and different ways of processing the image. B-mode or two-dimensional mode is basic ultrasound scanning. B stands for brightness. You scan a plane through the body that can be viewed as a two-dimensional image, on a screen in a grayscale of brightness. M-mode or motion mode, measures motion of particular structures, over time. A gate is placed on the ultrasound image and then M-mode demonstrates any motion along the structures
[00:00:30] of that gate. M-mode is often used for cardiac measurements and determining fetal heart rate. Here, you can see an example of M-mode showing a motion of the mitral valve in the heart. What is Doppler? Outside of a very complicated physics equation you see here? Well, it's a very useful mode of ultrasound that can give information on the direction and velocity of flow through structures. The Doppler shift is the difference in sound frequency between the ultrasound beam transmitted into the tissue and the echo produced by a reflection of
[00:01:00] moving red blood cells. While you don't necessarily need to memorize this equation, I do want you to know that there's a cosine in this equation, which refers to the cosine of the Doppler angle of insonation, which is the angle that the beam intercepts moving blood, within the blood vessel. But first, an easy way to remember what you're seeing on Doppler is to remember the word BART—Blue Away and Red Towards. Thus, the colors that you see on Doppler don't always correlate with blue for vein and red for artery.
[00:01:30] Here, you can see, that the probe on the left is angled to view the blood, as it is flowing away from it. Thus, the image will look blue on ultrasound. On the right, the probe is angled that the blood is coming towards the probe, thus, the image will look red on ultrasound. The cosine of 90 degrees is 0, thus, unlike most other scanning techniques, the ideal angle for scanning with Doppler is not perpendicular to the structure of interest. Instead,
[00:02:00] best is having the ultrasound beam hit the blood flow at about 60 degrees or there will be inaccurate information about the flow you're examining. If you angle the probe away from the heart or at a 120-degree angle from the vessel, the Doppler signature will show that flow is away from the probe in an artery and then appear blue. This gets confusing. The ideal angle for the ultrasound beam, hitting blood flow, is at 45 to 60 degrees. Conventional scanning is to point the transducer proximally to the structure you're scanning.
[00:02:30] Here, you can see the color of the vessel is red as the blood flow approaches the probe. Here, is what you'd see on ultrasound. On the left is a vein with blood flow away from the probe, and on your right is an artery with flow towards the probe. Spectral Doppler is the way to measure a velocity flow in a vessel. The machine will measure all the frequency shifts into a velocity. There are two forms. One is pulse wave and the other is continuous wave. There are two forms. Pulse wave, which looks at a single point
[00:03:00] on the image and sends a pulse then waits. Since there's a lot of waiting for the echo to come back, there's a limit as to how fast it can measure. In continuous wave, which you see on the right, which looks along a gate similar to M-mode and is constantly pulsing and listening. Here, you can see an example of pulse wave Doppler in an artery. You can see these high-velocity spikes. These correlate with the pulse. Here's an example of pulse wave Doppler in a vein. This is lower velocity
[00:03:30] than the artery and has a more undulating baseline than the spikes that you saw associated with pulse. When blood moves too fast, aliasing can occur as the machine cannot easily assign speed or direction to the blood flow. These filled-in velocity points then will occur above and below the baseline. So, those are all the modes of ultrasound. You did great. You even mastered a very complicated physics principle.