Which display modes may be used to calculate distance measurements?

• A. A-Mode Only
• B. B-Mode Only
• C. M-Mode Only
• D. A-Mode, B-Mode, and M-Mode

Answer: (D)

Distance measurements rely on depth information, which each ultrasound display provides in its own way. A-mode shows echoes as spikes against a depth axis, so you can directly convert the time delay of a return into a distance to the reflector using the known speed of sound in tissue. B-mode forms a 2D image with a depth scale; calipers can be placed between interfaces along that depth axis to read the separation, giving a distance measurement. M-mode traces depth over time along a single line, so you can read how far a structure is from the transducer at any moment or measure the distance between structures on the depth axis as it changes over time. Because all three modes encode depth, each can be used to calculate distance measurements.