Which ultrasound mode provides information about reflector location changing with time?

• A. A-mode
• B. B-mode
• C. M-mode
• D. Doppler mode

Answer: (C)

The idea being tested is tracking how reflector positions change over time along a single scan line. That is exactly what motion mode does. In this mode, the depth of interfaces is plotted as a function of time, producing a trace where moving structures appear as curves that shift up or down as time progresses. This high temporal resolution makes it ideal for observing rapid motions, like heart wall movement during the cardiac cycle.

Other ultrasound modes serve different purposes. A-mode shows a single depth-dependent amplitude spike for a location, without tracking motion over time. B-mode builds a two-dimensional image of reflector locations across an area, focusing on spatial positions rather than their time-based movement. Doppler mode analyzes frequency shifts to measure velocity of moving reflectors, giving speed information rather than a direct time-based position trace.