Which type of artifact is most closely associated with depth errors caused by incorrect sound speed assumptions?

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

Answer: (D)

The depth shown in an ultrasound image depends on the speed of sound used to convert travel time into distance. If the assumed speed of sound is not the actual speed along the tissue path, the time-to-depth conversion is off, so echoes are placed at incorrect depths — this is a speed error artifact.

For example, if the system assumes a speed higher than the true speed, a reflector at a given true depth will be placed deeper in the image (d_calc = d_true × (c_assumed / c_actual) > d_true). If the assumed speed is lower than the actual speed, the reflector will appear shallower. This misplacement occurs along the beam axis and directly results from using an incorrect sound speed in the depth calculation.