The height of the upward deflection in A-mode is proportional to which quantity?

• A. The amplitude of the returning echo
• B. The depth of the reflector
• C. The frequency of the transmitted pulse
• D. The speed of sound

Answer: (A)

In A-mode ultrasound, the vertical height of the trace represents the strength (amplitude) of the returning echo, while the horizontal position corresponds to depth (determined by the time it takes for the pulse to return). The height of the upward deflection is therefore proportional to the amplitude of the echo, which reflects how strongly the tissue interface reflects the ultrasound energy (impedance difference). The depth is set by how long the echo took to return, not by how tall the spike is. The frequency of the transmitted pulse affects resolution and wavelength, not the height of the echo on an A-mode trace. The speed of sound in tissue is used to convert travel time into depth, but it does not change the echo’s amplitude.