M-mode is 'motion mode". M-mode is used to evaluate the motion of interfaces that lie along a single scan line. The M-mode scan line is positioned within the region of interest using the trackball. Once positioned, the motion of any interface lying along the M-mode scan line is shown in a graphical display that scrolls from left to right across the screen. Non-moving interfaces will be displayed with a horizontal line. Interfaces that are moving either towards or away from the transducer will be displayed as a wavy line on the M-mode display. The primary uses for M-mode lie in the evaluation of the adult and fetal heart.
For more detail, please see the video file below. It contains a short narrated slide show on M-mode.
Remember, M-mode is low intensity compared to pulsed Doppler. Do NOT use pulsed Doppler to obtain a fetal heart rate. Use M-mode.
M-mode is awesome!