I’m Mike, and I recently joined the Portable Ultrasound Machines (PUM) team. When I started work with PUM, I didn’t have a background in ultrasound. So to help me get up to speed, I kept a note of all the new terms I was coming across along with a short definition.
This is the third in a series of blog posts sharing some of these with you. I hope you’ll find them a useful introduction to the – sometimes confusing! – language used in this sector and that they will help you if you are just beginning your journey with ultrasound and the machines we use.
In my first post we introduced the ‘transducer’ (also known as a probe). In that article we touched on how the choice of transducer can influence image quality. The second post outlined four interlinked terms all of which will influence the quality of the picture you will see: frequency, depth gain and resolution.
This third post moves on to think specifically about the components of ultrasound, and se-mystifies what we mean when we refer to the ‘B’, ‘M’, ‘A’ and ‘D’ modes on our machines.
Ultrasound consists of four components
We previously thought about frequency, depth, gain and resolution. All of these terms refer to work you can ask your machine to do on the image being returned to the transducer in order to enhance it in some way.
However, when you hear users and educators discuss the different ‘modes’ of an ultrasound machine, they are typically referring to ‘what’ the machine is looking for and the method it uses to do interpret and display what is found.
Each mode will be particularly suited to a specific job. There are typically four modes:
- Brightness mode (B-mode) is ideal for showing bone, organs and soft tissue.
- Motion mode (M-mode) tends to be used extensively in echocardiography.
- Amplitude mode (A-mode) is rarely used except for very specialist applications like backfat measurement in pigs.
- Doppler mode is particularly effective at making blood flow visible.
Selecting the mode is as simple as selecting the correct button on the machine (and may also involve a change of transducer). Not all machines will have all of these modes, however I will briefly summarise each one below.
You will find that B Mode is often the default mode of imaging for conventional animal ultrasound machines. Stronger echoes are received from more dense material such as dense tissue and bones, and in B-mode are shown as brighter pixels on the screen. Weaker echoes are received from softer materials such as heart chambers, fluid-filled structures or soft tissue. These are displayed as darker pixels
As its name suggests, M Mode (or Motion mode) allows us to view movement over time along a given ultrasound line. Producing a one-dimensional image, it is particularly helpful in the study of the heart (including its valves and walls). The motion of the tissues is tracked along the graph at the bottom of the image
Perhaps the least-often used mode in the ultrasound scanning of animals, we tend to see it most popular amongst those looking to assess the depth of backfat in pigs. This is because it scans a line through the body of the animal, showing how the echo response changes as the depth increases. When displayed, on the X axis/horizontal axis we see depth, whilst on the Y/vertical axis we see the amplitude (strength) of the echo response. When the waves are reflect from different densities of materials, we see distinct peaks and troughs, allowing us to assess how deep each layer of material is. It can also be used for ensuring the accurate targeting of radiation when treating tumours or similar.
Doppler mode is particularly helpful in making blood flow visible, interpreting the sound waves as colours so that we can see the speed and direction of blood flow in real time. Rather than being an entirely distinct imaging technique, it is in effect ‘layered’ on top of a standard B-Mode image. The colours represent direction of blood flow, and typically range from light blue to dark blue away from the transducer, and light red to dark red toward the transducer. This is another helpful mode for use in the diagnosis and treatment of echocardiography cases, and includes use in veins and tendons.
It should also be noted that there are sub-categories of Colour Doppler imaging, which may be the subject of a future blog. Very briefly, these include:
- Pulsed Wave Doppler (PWD): Short pulses of ultrasound are emitted and analysed, more often used in low-speed/velocity contexts.
- Continuous Wave Doppler (CWD): Rather than short pulses, ultrasound is continuously emitted and analysed, more often used in high-velocity/speed contexts.
- Power Doppler: Can tell us whether there is motion/flow present but cannot tell us the speed (velocity) of this motion/flow. Highly sensitive and ideal for low blood-flow contexts.
- Tissue Doppler: A further echocardiography use, specifically focused on the velocity of the heart muscle.
What have we learnt?
- The versatility of ultrasound for use in animals (and, indeed, humans) is incredible. We have used the four main components of ultrasound as a way to briefly explore this.
- There are four principal ‘components’ of ultrasound, which require different settings on the machine to be selected, and sometimes a different probe to be used for optimum results.
- These settings (or modes) can be summarised as ‘B’, ‘M’, ‘A’ and ‘D’ modes.
- B-mode is the ‘default’ setting and is most commonly used for showing tissue and bone structures, with lighter pixels representing more dense material and darker pixels representing less dense material.
- M-mode allows us to view movement over time expressed as a one-dimensional line in an ultrasound image, and is sometime used in the study of the heart.
- A-mode is most often used, in our sector, for the assessment of backfat depth in animals, providing a linear depiction of wave amplitude across a given depth.
- M-mode allows us to see volume and direction of blood flow (although it should be noted there are extensive variations within M-mode which influence the image you will see).
- The frequency, depth gain and resolution settings on your machine, discussed in the previous blog, can each be used to help improve the image you can see on-screen.
We hope you have found this third article interesting and a helpful ‘starting point’ in thinking about the different modes of your ultrasound machine and how they can help you in your work. Please look out for our next ‘beginners guide…’ blog coming soon.
If you would like to discuss any questions you have we would be delighted to speak with you (with no obligation to purchase a scanner from us). We are proud to offer the experience of professional sonographers with a combined experience of over 25 years and should you purchase from PUM will always be available to answer your questions and solve your problems. Free of charge, whenever you need us, we are here to help.