Which ultrasound mode has Time on the x-axis?

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

Answer: (C)

Time on the horizontal axis is a hallmark of M-mode because it records motion along a single ultrasound line over time. In this mode, the vertical axis represents depth along the beam, and as time progresses, the display moves horizontally to show how the depth of tissues changes. This creates a time-depth trace that is ideal for tracking motion, such as heart wall movement, with precise timing and excursion along that line.

A-mode, by contrast, is a simple depth versus amplitude plot along the beam and does not depict motion over time. B-mode builds a two-dimensional image where the axes represent spatial positions across the body, not a time axis. Doppler modes focus on motion information like velocity; while they can be shown as waveforms over time, they are not the single-line depth-over-time trace that defines M-mode.