I have a basic question concerning ultrasound A-scans. Such an A-scan might typically look as follows (source: https://img.medscapestatic.com/pi/meds/ckb/18/7418tn.jpg):
I understand that the x-axis is the time axis but I'm unsure about the y-axis. In the literature, I can find that the y-axis and the amplitudes of the signal represent the "intensity of reflected sound" but what's the unit of this intensity? Or to put it in other words: What would an amplitude value of, say, 0.2 actually mean?
Thank you very much.
Best Answer
The amplitude is just arbitrary units for relative measurements only. The absolute values don't really matter all that much.
The peaks in the graph represent changes in tissue properties — specifically, changes in acoustical impedance, which cause energy to be reflected back toward the source. It is the horizontal position (representing distance) and width of these peaks that is more relevant than their amplitude. Indeed, you can see that some of them "saturate" the receiver — they have flat tops.