One way that we could represent the motion from lung sliding in a still image is to use M-mode or motion mode, and this is where you take a one dimensional line put it across the pleural line and look at it over time and when you do that you can see that the portion of the image on the left has an area where there is motion represented in the inferior half of the field, this is called the “seashore sign” it looks sort of like waves coming into the beach and its nice and happy and normal.
Now if you’re looking at the pleural line and there is no motion we’ll get what we call the barcode sign also sometimes called the stratosphere sign and it basically shows there is no motion and it will look the same throughout the field.
Normal lung sliding
PTX - no sliding
So here’s a comparison labeled the seashore sign which is using m-mode showing motion on the left and that’s normal and then the barcode or stratosphere sign on the right where you don’t have motion at the pleural line so it looks the same from front to back on the left portion of the image.