At this point, you should feel confident about how to obtain the lung images.
If you do not feel confident, please review the slides.
If you do feel confident – now move on to answering the focused questions.
The focused questions in focused ultrasonography of the lungs are:
Learning objectives for focused ultrasonography of the lungs
Obtain
– Anterior intercostal view (‘bat-sign’)
– Posterolateral pleural view
Answer the focused questions
– Can pneumothorax be confirmed or excluded?
– Are signs of pulmonary edema present or can pulmonary edema be excluded?
– Can pleural fluid be confirmed or excluded?
A high frequency linear transducer or a curved (abdominal) transducer can be used for focused lung ultrasonography.
A linear high-frequency transducer is recommended if the purpose is only to visualise the pleural line (described later). The linear transducer has an optimal balance between resolution and depth for visualising superficial structures. It cannot be used for evaluating pleural fluid.
A lower-frequency transducer (abdominal or cardiac) permits the deep penetration that is needed for evaluation of pleural fluid (described later). The curved abdominal transducer also generates usable images for visualising the pleural line.
Tips
The ‘abdominal’ transducer can be used as an all-round transducer for focused lung ultrasonography.
Some cardiac transducers also allow fair imaging – but test your own equipment.
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.
Use this strategy when scanning:
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.
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.
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.
The ultrasound image can be optimised by adjusting different user controls.
The most important user controls are:
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.
