Seashore and Barcode in M mode
What is M mode?
- we will discuss 2 signs found on M mode for lung ultrasound:
- Seashore (Waves on the Beach) sign
- Barcode sign
M mode is a simple mode of ultrasound. In 2D ultrasound (what we are all familiar with), a 2 dimensional picture is created by multiple beams coming out of the ultrasound probe (left image). In M mode, only 1 beam is coming out of the probe (image on right) and this one beam records an image. A few milliseconds later, it does this again and the next image is placed BESIDE the first image.
In the image on the left, the ultrasound beam is seen within the 2D image. In the right hand image, the yellow arrow shows how this single beam lines up images creating the M mode image. As time goes forward, these single lines are printed on the screen very closely beside each other.
Seashore (Waves on the Beach) Sign
Now crank up your imagination! The superficial component looks like waves approaching the beach. The pleural line is the surf break. The lung artifact component looks like the sand on the beach. Go grab your Speedos!
- the seashore sign is a normal finding and represents lung sliding
- the thick bright white line on the tracing is the pleural line
- superficial to the pleura ( chest muscles, skin, fat ) is not moving, creating the solitary linear lines indicating a lack of motion
- deep to the pleura is lung sliding causing irregular grainy ‘noise’
- when there is no movement, M mode creates straight lines (as seen in the "ocean" above)
- if there is no lung sliding, then there is no movement anywhere on the screen
- the barcode sign occurs when lung sliding is absent
- the barcode sign is an abnormal finding
- tip a barcode on its side to see the similarities (this is the barcode from my pair of men's Speedos)
- M mode is a very primitive form of ultrasound
- time is the axis moving from left to right on the screen
- the Seashore sign is a normal finding
- the Barcode sign indicates loss of lung sliding