Which measurement determines the pixel brightness or intensity in ultrasound imaging?

• A. How strong the echo was
• B. How long it took the echo to be received
• C. The depth of the structure
• D. The speed of sound in tissue

Answer: (A)

Pixel brightness in ultrasound comes from the strength (amplitude) of the returned echo. When a pulse hits an interface with a big impedance difference, more energy is reflected back, producing a stronger echo that the system converts into a brighter pixel. The image’s grayscale values thus encode how strong the echo was, i.e., how reflective the tissue boundary is. The time it takes for the echo to return determines where the pixel sits along the depth axis, and the speed of sound in tissue is used to translate that travel time into depth, not to set brightness. So the measurement that sets how bright a pixel appears is the echo strength.