The accuracy of reflector depth position on an A-mode, B-mode, or M-mode display is called?

• A. range resolution
• B. axial resolution
• C. depth calibration
• D. speed error artifact

Answer: (C)

Depth calibration is the process that ensures the distance along the ultrasound beam shown on A-mode, B-mode, or M-mode matches the true physical depth. Echo time is converted to depth using the presumed speed of sound in tissue, and if that scale is off or the system isn’t aligned, all depths shift. By using a reference with known dimensions (like a calibration phantom), the display’s depth axis is adjusted so a reflector at a known depth appears at that exact depth on the screen. This accuracy in where things are placed along the depth axis applies across all modes, since they share the same depth measurement basis.

Range (axial) resolution is about how closely two reflectors can be spaced along the beam and is not about absolute depth accuracy. A speed error artifact is a consequence of incorrect speed settings causing depth distortion, but the corrective and descriptive term for accurate depth positioning is depth calibration.