Functions and Settings of the Ultrasound Machine
In this video, we'll give you a basic introduction to ultrasound scanning.
It's designed for the complete beginner, so don't worry if any of the terminology is new to you; we'll explain it as we go along.
To generate reliable images and interpret them correctly, you need to understand the
basic functions of the ultrasound machine and how to set them up. Most important is
learning how to set up the B-mode image, which you'll use in almost all scans.
On most modern machines, the basic ultrasound functions are controlled using the knobs and
buttons of a console. The position and appearance of the controls vary, so you should familiarize
yourself with a new machine before getting started. However, most of the basic functions
can be found relatively easily on all machines. More complex or manufacturer-specific functions,
like 3D ultrasound, are not covered in this video.
Setting up the B-mode image
At the start of every scan, the B-mode image should be optimized to best display the area of interest.
In this example, we're using a curvilinear probe to show a transverse scan of the upper abdomen.
We'll now adjust the image to show the aorta and inferior vena cava as clearly as possible.
Gain
At the moment, there are a lot of dark areas in the image that are effectively information-free.
We can make these clearer by increasing the amplification of the reflected ultrasound signal in the image,
the so-called “gain.”
On this machine, gain is controlled using a rotary control in the middle of the console,
similar to a volume knob.
Increasing gain makes the entire image brighter.
If gain was previously set too low, as shown here, increasing it can make it easier to distinguish structures
of interest. But the gain should not be set too high either, because this "overgain" will
make the image too bright, amplify noise, and reduce your ability to differentiate tissues.
Depth
To best assess your structures of interest, they should be displayed as largely as possible and centered on the screen. We do this by
adjusting the penetration depth of the ultrasound signal to the minimum required to still allow
all structures of interest to be visualized. On the machine shown here, this is done using
the rotary control labeled “DEPTH/ZOOM."
Focus
Image resolution can be selectively increased in the area of interest by adjusting the focal zone.
On the machine shown here, this is done using another rotary control.
The changing focal zone is shown by a moving arrow on the left side of the image.
Documentation functions
Freeze function
When performing a scan, it can be very helpful to “freeze” the image at a specific point in time.
You can do this using the freeze function.
On the machine shown here, the freeze button is labeled “F-R-Z” and is located on the lower right of ​​the console.
Pressing the button freezes the current image.
Once you've pressed freeze, most machines allow you to scroll back through the most recent frames to select the best one.
On the machine shown here, you can scroll using the trackball in the center of the console,
and pressing the Freeze button again returns to the real-time image.
Performing measurements
Once you've frozen the image, you can also perform measurements.
On the machine shown here, this function is activated by pressing the "CALIPER" button.
Next, confirm the starting point of your measurement by pressing the "SET" button,
then use the trackball to navigate to the end point.
Press "SET" again to confirm and display the result.
Pressing the "NEXT" button allows you to take another measurement.
Other ultrasound modes
In addition to B-mode, there are other scanning modes that provide further information.
We'll look at two of these next:
Color Doppler mode, and M-mode.
Color Doppler mode
Color Doppler mode is used to look for the presence of flow, usually the movement of blood in arteries and veins.
On the machine shown here, this function is activated and deactivated by pressing the "CDI" button, which stands for "Color Doppler Imaging."
Other manufacturers label this differently, for example, "C" for "Color" or "CF" for "Color Flow."
When color Doppler mode is activated, a box appears on the screen.
Within that box, flow toward the probe will appear red, and flow away from the probe will appear blue.
Keep in mind that as with B-mode, color Doppler mode has to be set up correctly to achieve the best results
and avoid misleading findings.
You can, for example, adjust the gain of color Doppler mode similarly to how you adjust B-mode gain,
but the details are beyond the scope of this introductory video.
M-mode
"M-mode" stands for "Motion-mode" and is activated on this machine by pressing the "M" button.
This projects a cursor line over the B-mode image and brings up a diagram, seen here on the left side.
The diagram plots the B-mode image along the cursor line over time.
The concept is similar to that of a flip book
- with the difference that images are displayed side by side rather than one behind the other.
This allows us to visualize the movement of the structures along the cursor line over time.
The position of the cursor line can be changed using the trackball.
On this machine, pressing the "M" button again exits the mode.
Okay, now that you have an overview of the basic functions and settings of an ultrasound machine,
check out the POCUS article on AMBOSS.