In ultrasound imaging, which mode is best for tracking motion along a single line, such as cardiac walls?

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

Answer: (B)

Tracking motion along a single line relies on capturing how tissue positions change over time along that line. M-mode does this by repeatedly sampling the same line and presenting depth along the vertical axis with time along the horizontal axis. The result is a one-dimensional trace where moving cardiac walls appear as wavy lines, making it easy to measure motion amplitudes, wall thickening, and timing within the cardiac cycle. Because it keeps sampling the same line, the temporal resolution is much higher than in standard 2D B-mode imaging, so rapid cardiac motions are resolved without blurring.

B-mode creates two-dimensional images with good spatial detail but lower temporal resolution for each line; it shows anatomy, not precise motion over time along a single axis.

Doppler mode is excellent for measuring velocity along the beam and detecting flow, and it can show motion information, but its primary output is velocity information over time rather than a continuous depth-position trace of structures along that line.

Elastography visualizes tissue stiffness, not motion over time, so it isn’t used to track wall motion.

Hence, for tracking motion along a single line such as cardiac walls, a mode that provides a time-evolving depth trace on that line is the best option: M-mode.