What is displayed on the y-axis of an M-mode image?

What is displayed on the y-axis of an M-mode image?

• A. Time
• B. Time-of-flight
• C. Reflector depth
• D. Red blood cell velocity

Answer: (B)

In M-mode ultrasound, a single scan line is followed over time to show motion, so the horizontal axis represents time. The vertical axis shows how deep the echoes come from, i.e., the distance from the transducer to the reflector. That depth is derived from the round-trip travel time of the ultrasound pulse—the time-of-flight—using the speed of sound in tissue. In other words, what the vertical axis reflects is depth as calculated from time-of-flight.

In M-mode ultrasound, a single scan line is followed over time to show motion, so the horizontal axis represents time. The vertical axis shows how deep the echoes come from, i.e., the distance from the transducer to the reflector. That depth is derived from the round-trip travel time of the ultrasound pulse—the time-of-flight—using the speed of sound in tissue. In other words, what the vertical axis reflects is depth as calculated from time-of-flight.