Which of the following best describes M-mode?

• A. Presentation of Reflector Amplitudes Along Multiple Lines of Sight
• B. Two-Dimensional Gray-Scale Image
• C. Movement of a Single Structure Along Multiple Lines of Sight
• D. Depth of Reflectors Along a Single Line of Sight vs. Time

Answer: (D)

Motion mode (M-mode) is ultrasound that shows how echoes from along a single scan line change over time. It plots depth along that line on one axis and time on the other, producing a trace of reflector positions as they move. This snapshot is specifically about how a structure moves along that one line of sight over time, not about creating a two-dimensional gray-scale image or comparing multiple lines. So the best description is depth of reflectors along a single line of sight versus time. This mode is especially useful for tracking motion, such as heart valve movement, along a single beam.