Which of the following is NOT user-adjustable?

• A. Frequency
• B. Power
• C. Echo arrival time
• D. Gain

Answer: (C)

In ultrasound systems, some controls let you change how the signal is generated or amplified, while others relate to the fundamental timing of the sound waves themselves. You can adjust the transmit frequency to trade resolution for penetration, adjust the output power to change how strong the emitted pulse is, and adjust the gain to brighten or darken the echoed signal you receive. These knobs change the signal processing or the energy you send or receive.

The echo arrival time, however, is determined by how far away a reflector is and how fast sound travels through the medium. That timing is a physical property you can’t change with a control. You can shift where you look on the screen by changing the depth setting, which alters which echoes appear at which display times, but you don’t alter the actual travel time of the echoes themselves. Because of that, echo arrival time is not user-adjustable.