The image shows an ultrasound image of the heart with different gain settings. The top image is undergained, the middle has optimised gain, and the bottom image is overgained.
Undergain If the user sets the gain control too low, the result is that the amplification of the electrical signals becomes too small and the 2D grayscale image on the screen becomes too dark.
Overgain If the user sets the gain control too high, the result is overamplified electrical signals including artefactual noise and the 2D greyscale image becomes too bright (white) with loss of resolution.
This ends the lesson on ‘Understanding Ultrasound’
Before you can start the next lesson you must test yourself in a little quiz – results are for you only. Nothing will be stored.
To ensure maximum transmission of ultrasound into the tissue, the application of ultrasound gel is very important.
Remember always to use a sufficient amount of gel.
The video shows two different ultrasound images of the same blood vessel at the wrist in the same patient, when sufficient and insufficient amounts of ultrasound gel is used. In the upper image the probe is placed on a “dry” arm, and in the lower image a sufficient amount of gel was used.
Bone and air do not allow ultrasound penetration. Since most of the thorax consists of bone and air it can be hard to find ‘a passage’ through which the ultrasound waves can travel to get an image of the deeper structures e.g. the heart.
Such an area of passage is called an ‘acoustic window‘.
Acoustic windows are often small with a narrow passage for the ultrasound waves.
Depth should be optimised to target the structure of interest in the centre of the monitor and to visualise the entire target structure inside the visual field.
The image shows an ultrasound image of the heart with different depth settings. The top image is too shallow, the depth of the middle image is appropriate, and the depth of the bottom image is too large.
The image is generated by the transducer and the ultrasound system and displayed on the screen.
The sector is demarcated by the two radii and the arc. In the illustration below, the two radii of the sector are red and green.
The red and the green radii diverge from the probe at the top of the monitor (the skin surface).
By convention, the orientation indicator (OI – blue dot on the screen) is on the left side of the screen in conventional clinical ultrasound applications (it is the opposite in cardiac ultrasound, where the OI is placed on the right side of the screen).
When orienting the orientation marker (OM – blue dot on the transducer) to the same side as the OI on the screen, the red radius of the ultrasound beam sector corresponds to the red radius of the ultrasound image sector, and the green radius corresponds to the green radius of the ultrasound image sector.
The image shows the ultrasound sector produced by the probe and the corresponding ultrasound image on the ultrasound screen. Notice that the OM on the left side of the transducer corresponds to the left side of the screen. The right side of the ultrasound sector (green) corresponds to the right side (also green) of the screen.
A shared terminology to describe the movement of the transducer during scanning is important in order to optimize the image.
During the workshop it makes it easier for the supervisor to give instructions without touching the transducer which is crucial for the novice in order to achieve practical skill.
There are many available descriptions of the method of manipulation of the transducer.
We recommend using: 1. rotate (right – clockwise, left – counterclockwise) 2. rock (in-plane motion away or toward the indicator) 3. tilt (angling the transducer – perpendicular to rocking) – sweep (is tilting with a continuous fanning motion back and forth) 4. slide (moving the transducer on the skin)
As a novice you should only manipulate the transducer in one direction at a time.
Figure showing movements in three different spatial directions. Confused? Look at the video in the next topic!
The image on the ultrasound monitor represents a thin slice of tissue.
The size of the slice is determined by the profile of the ultrasound beam and can be described by height, width and thickness.
The ultrasound beam thickness is approximately 3-8 mm.
The width in the proximal part of the image is determined by the width of the footprint of the transducer. The width in the distal part of the image can be changed when using curved transducers – this is most often not needed in focused emergency ultrasonography.
Height can be changed by adjusting the image depth on the ultrasound system.
Moving the transducer on the surface of the skin, rotating and tilting the transducer allows you to capture the best possible cross-sectional view of your target structure in the best possible position.
The OM facilitates the correct orientation of the transducer when scanning the patient.
The OM has to be oriented correctly with the corresponding orientation indicator (OI) on the monitor.
When in doubt use the “finger-on-transducer” test explained in the video below – press the PLAY triangle to watch the video
The video-clip shows the “finger-on-transducer” test – touching of the left side of the transducer is displayed as a movement in the ultrasound image on the left side of the screen when the probe is oriented correctly.
