Most ultrasound imaging is performed in B-mode (brightness), which is the standard, two-dimensional representation of the reflected ultrasound waves As described above, each pixel represents the intensity and distance (determined by time) of a returning sound wave M-mode (motion) essentially creates a single line of a sound wave through an object of interest, and then displays that image with respect to time (on the horizontal access) M-mode is useful to document movement of a structure, such as cardiac valves or the fetal heart Finally, D-mode (Doppler) and Color Flow Doppler sense the movement of the ultrasound waves as they encounter a moving medium, represented by either color changes or sound from the ultrasound machine Color Flow Doppler ultrasound is especially useful when identifying vessels and discerning between arterial and venous flow The colors represent flow away from or toward the probe and not correlate with arterial or venous flow ( Video 131.1 ) FIGURE 131.3 Image of femoral anatomy Note the marker on the screen (arrow ) is a green dot By convention, the marker should always be on the left, upper side of the monitor DIAGNOSTIC APPLICATIONS Focused Assessment With Sonography in Trauma The use of sonography in trauma was one of the very first applications of emergency POCUS, and many now consider it a standard part of the evaluation of